Aspirin for the Prevention of Cardiovascular Events in Patients Without Clinical Cardiovascular Disease

A Meta-Analysis of Randomized Trials

                    Jeffrey S. Berger,; Anuradha Lala,; Mori J. Krantz,; Gizelle S. Baker, PhD; William R. Hiatt,
                                                                                        American Heart Journal. 2011;34(3):115-124.

Abstract

Background The benefit of aspirin to prevent cardiovascular events in subjects without clinical cardiovascular disease relative to the increased risk of bleeding is uncertain.
Methods A meta-analysis of randomized trials of aspirin versus placebo/control to assess the effect of aspirin on major cardiovascular events (MCEs) (nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death), individual components of the MCE, stroke subtype, all-cause mortality, and major bleeding. Nine trials involving 102,621 patients were included: 52,145 allocated to aspirin and 50,476 to placebo/control.
Results Over a mean follow-up of 6.9 years, aspirin was associated with a reduction in MCE (risk ratio [RR] 0.90, 95% CI 0.85-0.96, P < .001). There was no significant reduction for myocardial infarction, stroke, ischemic stroke, or all-cause mortality. Aspirin was associated with hemorrhagic stroke (RR 1.35, 95% CI 1.01-1.81, P = .04) and major bleeding (RR 1.62, 95% CI 1.31-2.00, P < .001). In meta-regression, the benefits and bleeding risks of aspirin were independent of baseline cardiovascular risk, background therapy, age, sex, and aspirin dose. The number needed to treat to prevent 1 MCE over a mean follow-up of 6.9 years was 253 (95% CI 163-568), which was offset by the number needed to harm to cause 1 major bleed of 261 (95% CI 182-476).
Conclusions The current totality of evidence provides only modest support for a benefit of aspirin in patients without clinical cardiovascular disease, which is offset by its risk. For every 1,000 subjects treated with aspirin over a 5-year period, aspirin would prevent 2.9 MCE and cause 2.8 major bleeds.

Introduction

Aspirin is effective in decreasing cardiovascular morbidity and mortality in patients with clinical evidence of cardiovascular disease (CVD).^[1,2] Specifically, benefits of aspirin are well defined for secondary prevention of acute myocardial infarction (MI) and stroke, forming the basis for current clinical practice guidelines.^[3-6] These responsive populations include patients who have experienced plaque rupture or vessel occlusion sufficient to induce a symptomatic state (eg, stable angina^[7] or transient ischemic attack),^[8,9] acute coronary syndrome,^[10-12] or ischemic stroke.^[13] The data demonstrating benefit of aspirin in patients without clinical CVD are less certain.^[14,15] This includes populations at risk based on age, risk factors such as diabetes or hypertension, or evidence of subclinical atherosclerosis.^[16] Clinical decision making is further complicated by several meta-analyses of the older trials that found a significant decrease in the composite of major cardiovascular events (MCEs) by approximately 12%,^[17,18] but newer trials of aspirin in patients at high risk but without clinical CVD have failed to achieve their primary end points.^[19-21] Thus, the benefit-to-risk relationship needs further definition in light of the newer evidence.
The most recent meta-analysis reviewed 6 primary prevention trials and concluded that current evidence did not clearly support a net benefit of aspirin relative to the excess bleeding risk in primary prevention.^[17] This analysis did not identify any potential subgroups as response modifiers including age, gender, diabetes or other risk factors, or predicted 5-year risk of CVD. However, the publication of 3 new trials in at-risk populations allows for further evaluation of these potential risk modifiers. Thus, the current meta-analysis includes new data and tests the null hypothesis on the available data that there is no net benefit relative to risk for aspirin when used in patients without clinical CVD.

Methods

Search Strategy

From 1966 to 2005, a computerized search was performed that identified 6 published randomized trials of aspirin in patients without clinical CVD. In the previous meta-analysis of these trials, aspirin therapy significantly reduced the risk of an MCE (nonfatal MI, nonfatal stroke, or cardiovascular death) by 12% in women and 14% in men.^[18] From 2005 to the present, a subsequent review of the literature (MEDLINE, the Cochrane Central Register of Controlled Trials, and EMBASE) identified 3 additional primary prevention studies of aspirin for a total of 9 trials for analysis.^[19-21]

Study Selection

Primary prevention trials that involved a randomized comparison of aspirin versus placebo or control in patients without clinical CVD (eg, established or symptomatic) were included in this analysis. The criteria for inclusion of trials were as follows: (1) aspirin alone was used for the primary prevention of CVD; (2) comparisons of outcomes were made between aspirin and placebo or open control groups; and (3) data were available on MI, stroke, and cardiovascular deaths. Our search included only those studies published in English.

Outcome Measures

The primary outcome was the risk ratio (RR) of aspirin therapy compared with placebo or control on the composite MCE end point, which includes nonfatal MI, nonfatal stroke, or cardiovascular death. Secondary outcomes included all MI, all stroke, all-cause mortality, and cardiovascular mortality. The primary safety outcome was the occurrence of major bleeding as defined by each study. Because the definition of major bleeding differed by trial, gastrointestinal hemorrhage and cerebral hemorrhage were reported separately. In addition, stroke subtypes (ischemic or hemorrhagic) were examined from data available in the 8 studies that reported strokes by subtype. The adjudication process to subtype stroke was not provided for all the trials. The HOT trial^[22] did not include data by stroke subtypes.

Statistical Analysis

The composite end point was analyzed using the data as they were reported in the included publications. A random-effects model was the primary analysis because of the differences across the studies in patient characteristics (including underlying disease population) and aspirin dosing. To determine the appropriateness of pooled RR estimates, heterogeneity among the trials was examined using the Q statistic for each of the end points analyzed. It was determined that pooled estimates from the random-effects model of the RR were reasonable because the Q statistic did not indicate statistically significant heterogeneity and the I ² statistic was <37% for all end points other than fatal and nonfatal MI. For the MI end point, there was moderate heterogeneity (63% of variation because of heterogeneity) that was statistically significant.
A sensitivity analysis of the primary analysis was performed to examine the robustness of the results. This was done by examining the impact of systematically removing 1 study from the analysis and recalculating the results. In addition, specific subsets of the studies were analyzed to evaluate the consistency of the effects of aspirin when studies that were restricted to persons with diabetes were excluded,^[19,21] studies enrolling patients with subclinical atherosclerosis (by a low ankle-brachial index [ABI]) were excluded,^[19,20] and studies that included extended or controlled release aspirin were removed.^[20,23,24] In addition, the data were analyzed using a fixed-effect model, and the results were compared with the random-effects model.
Linear meta-regression analyses on the log-transformed RR with the study as the unit of analysis were performed to evaluate potential effect modifiers (year of study publication, baseline cardiovascular risk as assessed by incidence of events on placebo, mean age of the trial participant, sex, and dose of aspirin). Studies were weighed by the precision of the effect estimate.
The potential publication bias was examined by constructing a funnel plot in which sample size was plotted against log RRs for the primary end point available from all studies.
Statistical analyses were performed using Review Manager 5.0.23 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark, 2008). P < .05 was judged as statistically significant

Results

Nine prospective randomized trials involving 102,621 participants were identified for inclusion. A total of 710,053 person-years of exposure were recorded: 359,709 in the aspirin group and 350,344 in the placebo or control group. All trials included patients without clinical CVD, which was defined as the absence of a cardiovascular event, or clinical symptoms of CVD including angina or transient ischemic attack. Among the 3 new trials,^[19-21] 2 included only diabetic patients,^[19,21] and 2 required a low ABI measurement as a marker of subclinical atherosclerosis for inclusion.^[19,20] Of the 9 trials, 3 included only men,^[23-25] and 1 included only women.^[26]
Dosage of aspirin ranged from 100 mg every other day to 500 mg daily. Two trials used enteric-coated aspirin,^[20,24] and 1 trial used a longer preparation tablet.^[23] Follow-up ranged from 4.4 to 10.1 years and was >95% complete in all trials. The weighted mean follow-up time was 6.9 years.

Major Cardiovascular Events

A total of 2,029 MCEs occurred among 52,145 (3.86%) patients allocated to aspirin compared with 2,099 MCEs among 50,476 (4.16%) patients assigned to placebo or control (Figure 1). Pooled results using a random-effects model demonstrated a significant 10% reduction in the risk of MCE (RR 0.90, 95% CI 0.85-0.96, P < .001). In aggregate, the absolute risk reduction was 0.39% (95% CI 0.18%-0.61%) over a mean follow-up of 6.9 years, which corresponds to a number needed to treat of 253 (95% CI 163-568) to prevent a single MCE.

Myocardial Infarction

A total of 993 fatal and nonfatal MI events occurred among 52,145 (1.90%) patients allocated to aspirin compared with 1,075 MI events among 50,476 (2.13%) patients assigned to placebo or control (Figure 2). Pooled results demonstrated a 14% risk reduction in both fatal and nonfatal MI, which failed to reach statistical significance (RR 0.86, 95% CI 0.74-1.00, P = .06). For the end point of nonfatal MI, there was a 16% reduction in events with aspirin versus placebo or control; however, the results did not reach statistical significance (RR 0.84, 95% CI 0.70-1.01, P = .06).

Stroke

A total of 741 fatal and nonfatal strokes occurred among 52,145 (1.42%) patients allocated to aspirin compared with 746 strokes among 50,476 (1.48%) patients assigned to placebo or control (Figure 3). Pooled results demonstrated a non significant 6% reduction in the risk of stroke (RR 0.94, 95% CI 0.84-1.06, P = .31). Eight of the studies provided data on type of stroke. For the end point of nonfatal stroke, there was a nonsignificant 8% reduction in events with aspirin versus placebo or control (RR 0.92, 95% CI 0.80-1.06, P = .26).
To further understand the benefit versus risk, the relationship of aspirin on ischemic and hemorrhagic stroke was explored independently (Figure 3). For the end point of ischemic stroke, there was a nonsignificant 13% reduction in events with aspirin versus placebo or control (RR 0.87, 95% CI 0.73-1.02, P = .09). For the end point of hemorrhagic stroke, there was a significant 35% increase in events with aspirin versus placebo or control (RR 1.35, 95% CI 1.01-1.81, P = .04). The absolute risk increase was 0.06% (95% CI 0.003-0.126) over a mean follow-up of 6.9 years, corresponding to a number needed to harm of 1,560 (95% CI 794-33,333) to cause 1 hemorrhagic stroke.

Death

A total of 1,962 deaths occurred among 52,145 (3.76%) patients allocated to aspirin compared with 1,933 among 50,476 (3.83%) patients assigned to placebo or control (Figure 4). Pooled results demonstrated a non significant reduction of 6% in the risk of death (RR 0.94, 95% CI 0.89-1.00, P = .07). For the end point of cardiovascular death, there was no reduction in events with aspirin versus placebo or control (RR 0.99, 95% CI 0.85-1.14, P = .86).

Major Bleeding

A total of 458 major bleeding events occurred among 52,145 (0.88%) patients allocated to aspirin compared with 278 major bleeding events among 50,421 (0.55%) patients assigned to placebo or control (Figure 5). Pooled results demonstrated a significant 62% increase in the risk of major bleeding (RR 1.62, 95% CI 1.31-2.00, P < .001). In aggregate, the absolute risk was 0.38% (95% CI 0.21%-0.55%) over a mean follow-up of 6.9 years, which corresponds to a number needed to harm of 261 (95% CI 182-476) to cause a single major bleeding event over 6.9 years. For the end point of gastrointestinal hemorrhage, there was a significant 29% increase in events with aspirin versus placebo or control (RR 1.29, 95% CI 1.24-1.47, P < .001).

Meta-regression

Linear meta-regression models were used to assess the impact of study-level covariates on the risk of MCE and major bleeding. There was no relationship between any of the covariates examined (year of study publication as a surrogate for any changes in background cardiovascular preventive therapies, baseline cardiovascular risk as assessed by incidence of events on placebo, mean age of the trial participant, sex of the trial participant, and dose of aspirin) and the effect of aspirin on MCE or major bleeding (see Supplemental Figures 6 and 7 in the online Appendix).

Aspirin Dose and Formulation

Although aspirin dose ranged from 100 mg every other day to 500 mg/d, 7 of the 9 trials used a dose between 75 and 162.5 mg/d. There did not appear to be any relationship between aspirin dose and the effect of aspirin on MCE or major bleeding.Three trials used a different aspirin formulation than regular aspirin. The BDT and AAA trials used an enteric-coated aspirin formulation, whereas the TPT trial used a controlled release formulation. When analyses were repeated after excluding these trials, the association between aspirin and the primary outcome of MCE yielded an effect size (RR 0.89, 95% CI 0.83-0.95) similar in magnitude and direction to the overall results.

Sensitivity Analysis

There was no difference in results between the fixed-effect (RR 0.90) or the random-effect model (RR 0.90) for the primary outcome of MCE. The RR varied between 0.891 and 0.893 when each study was systematically removed from the model. The POPADAD^[19] and JPAD^[21] trials exclusively enrolled patients with diabetes, and both demonstrated no significant effect on the composite of cardiovascular events. Because aspirin may not be beneficial in patients with diabetes,^[27] the primary analysis was repeated after excluding these 2 trials. The association between aspirin and the primary outcome of MCE yielded an effect size (1,868 events among 50,245 patients taking aspirin [3.7%] vs 1,924 events among 48,561 control patients [4.0%]; RR 0.90, 95% CI 0.84-0.96) identical to the overall results.
The AAA^[20] and POPADAD^[19] trials exclusively enrolled patients with subclinical atherosclerosis determined by a low ABI. Because aspirin may not be beneficial in patients with PAD,^[28] the primary analysis was repeated after excluding these 2 trials. A similar effect of aspirin was observed (RR 0.89, 95% CI 0.83-0.95) relative to the overall result.

Discussion

The current meta-analysis included 9 prevention trials in >100,000 subjects without clinical evidence of CVD treated with aspirin versus placebo or control for the prevention of ischemic cardiovascular events. The pooled results found a statistically significant 10% relative reduction in the primary end point of MCE and a statistically significant 62% relative increase in major bleeding events. The absolute benefit versus risk demonstrated that, in 1,000 patients treated for 5 years, there were approximately 3 ischemic events avoided that was associated with an excess of 3 major bleeds resulting in no net benefit to risk for aspirin in this population. These results were consistent across a number of subgroups suggesting that a more targeted approach to maximize benefit and minimize risk could not be identified.
The year of publication of the trials ranged from 1988 to 2010 and spanned over a decade during which there were major improvements in the medical prevention and treatment of CVD,^[29,30] yet publication year did not have either a positive or negative impact on the overall estimate of the benefit or risk of aspirin (Supplemental Figures 6A and 7A in the online Appendix). The risk of CVD events in the placebo/control groups was also quite broad, ranging from 0.25% per year in the Women's Health Study to 2.7% in the POPADAD trial (expressed over a decade per the Framingham coronary heart disease risk score this baseline risk ranges from 2.5% to 27%). Yet, using this baseline risk assessment or components of that risk including populations enriched with diabetes did not impact the estimate of benefit or risk of aspirin (Supplemental Figures 6B and 7B in the online Appendix). Cardiovascular risk estimates can also be significantly influenced by measures of subclinical atherosclerosis such as the ABI or carotid intima-media thickness.^[31-33] However, in the most recent AAA trial^[20] where a low ABI was used as an inclusion criterion or in the POPADAD trial^[19] where a reduced ABI and diabetes were inclusion criteria, the trials were not just statistically negative, but the point estimates of benefit in both were near 1.00. Finally, although the dose of aspirin ranged from 100 mg every other day (50 mg/d)^[26] to 500 mg/d,^[24] the dose of aspirin did not impact the results (Supplemental Figures 6E and 7E in the online Appendix). Taken together, aspirin retains a modest yet statistically significant benefit on decreasing nonfatal cardiovascular events. These benefits are offset by a consistent signal of major bleeding risk including hemorrhagic stroke. These new results need to be considered by clinicians making difficult decisions about the value of primary preventive pharmacotherapies (relative to drugs with unequivocal benefit such as statins and blood pressure medications).
The goal of the current study was to perform a comprehensive meta-analysis of all randomized trials with aspirin as preventive therapy in patients without established or symptomatic CVD. Previous meta-analyses^[17,18,34] have been restricted to older trials with lower risk populations and did not include all contemporary randomized trials. Twenty years ago, 2 landmark trials^[24,25] evaluated the effect of aspirin in primary prevention. Neither the BDT^[24] nor the PHS^[25] demonstrated a benefit for aspirin in the reduction of their primary end point  However, the PHS^[25] was able to demonstrate a decrease in the secondary end point of fatal and nonfatal MI by 44%, leading to the widespread recommendations and use of aspirin in primary prevention. Since then, there have been 4 randomized trials^{[22,23,26,35]} of aspirin in primary prevention and 3 more recent randomized trials^[19-21] in patients with diabetes and/or subclinical atherosclerosis (defined by reduced ABI). None of these 7 trials demonstrated a beneficial effect of aspirin on their prespecified primary end point If one were to evaluate the traditional composite end point of nonfatal MI, nonfatal stroke, or cardiovascular death, only 1 of the 9 trials was associated with a statistically significant reduction. Thus, the benefit observed in our meta-analysis with aspirin is only seen after combining all the data in aggregate.
Bleeding risk is consistently increased with aspirin therapy across the trials. Despite different definitions of major bleeding among the trials, there was a strong signal of increased risk. Of the 9 trials, 4 found a statistically significant increase in major bleeding, and in pooled analysis, the risk was increased by 62%. Hemorrhagic stroke is a less common but clinically important end point because of its significant morbidity. Incidence of hemorrhagic stroke increased by approximately 0.1% (1 per 1,000 patients treated); however, in the pooled analysis, aspirin was associated with a significant 36% increase in the risk of hemorrhagic stroke.
Because aspirin was associated with a significant reduction in cardiovascular events but a proportional increase in bleeding complications, it is essential to understand the absolute benefit versus risk. Three MCEs were prevented for every 1,000 patients treated with aspirin over a period of 5 years, at the cost of inducing 3 major bleeding events. Intracranial hemorrhage was statistically significantly higher in the aspirin group, but the number needed to harm was 1,560 (<1 in 1,000 patients treated).
There are several potential explanations for the lower-than-expected proportional benefit observed with aspirin in this trial data set. Trials included in this analysis spanned several decades, and during this period, there has been considerable improvement of outcomes with the adoption of statins and angiotensin-converting enzyme inhibitors.^[29,36] Although no significant heterogeneity was observed between proportional reduction in MCE and time of publication, 4 of 5 trials published before 2002 had a proportional reduction of >10%, whereas only 1 of 4 trials published after 2003 had such a benefit. Moreover, the larger proportional benefit (>15%) observed in trials of aspirin in patients with clinical CVD occurred in trials >15 years ago. Consistent with this hypothesis, the CHARISMA trial (published in 2006) tested clopidogrel plus aspirin versus aspirin alone in patients with and without clinical CVD and demonstrated a nonsignificant increased risk of MCE with combination antiplatelet therapy in the primary prevention subgroup of the trial.^[37] Thus, if aspirin alone is of uncertain benefit in these subjects, dual antiplatelet therapy may be even more suspect.
An additional explanation on the lack of a net benefit over risk may be that concomitant therapies have minor antiplatelet affects that may attenuate any potential benefit of aspirin. In fact, statins,^[38,39] fish oil,^[40] angiotensin-converting enzyme inhibitors,^[41,42] fibrates,^[39,43] phosphodiesterase inhibitors such as cilostazol,^[44] and selective serotonin reuptake inhibitors^[45] have all been shown to reduce platelet activity. Unfortunately, few of the aspirin trials reported concomitant medications and what, if any, modifying effect these medications may have on the effect of aspirin. Although some have suggested an attenuated effect of aspirin in certain high-risk groups, such as persons with diabetes^[27] and peripheral artery disease,^[28] there was no difference in the results when trials that exclusively enrolled those populations were excluded. Finally, dose and aspirin formulation differed across the trials, which may have contributed to the lower proportional benefit. However, there was no difference in the effect of aspirin when adjusting for aspirin dose or after excluding trials that used a longer acting or enteric-coated formulation.

Limitations

There are several limitations to this study. Some imprecision exists in the frequency of events because the protocols for data collection and definitions of efficacy and safety events varied among the studies. However, all of the trials allowed for the assessment of a common MCE outcome that served as a primary end point for analysis. For the safety end point, definitions of major bleeding varied across the trials, and these variations made it difficult to determine accurate measure of bleeding and approximate risk. Therefore, both gastrointestinal hemorrhage and hemorrhagic stroke were used as complementary end points to help evaluate risk.
The current meta-analysis was not performed on individual patient data because complete individual data were not available, and therefore, comprehensive assessment within different higher-risk groups was not able to be performed. Nonetheless, the analyses were able to adjust for the incidence of adverse events in the placebo group (a surrogate for baseline risk) in each individual trial, which had no effect on the overall results. A proportion of patients included in this meta-analysis had documented subclinical atherosclerosis, as detected by a lower ABI. Although some would consider this a limitation because of the higher-risk cohort included, no change in the effect of aspirin was observed after exclusion of these patients, and the results were nearly identical.

Conclusions

This meta-analysis of >100,000 randomized patients (>700,000 person-year follow-up) comparing aspirin versus placebo or control demonstrated that aspirin decreased MCE by approximately 10% among patients without clinical CVD. Major bleeding, however, occurred more frequently with aspirin therapy. The decision to use aspirin for the prevention of a first MI or stroke remains a complex issue. Weighing the overall benefit and risk requires careful consideration by the physician and patient before initiating aspirin for preventive therapy in patients without clinical CVD.

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Corticosteroids Influence the Mortality and Morbidity of Acute Critical Illness

                     Mohamed Y Rady; Daniel J Johnson; Bhavesh Patel; Joel Larson; Richard Helmers

                                                                                                      Crit Care. 2006;10(3)

Abstract

Introduction: Use of corticosteroids for adrenal supplementation and attenuation of the inflammatory and immune response is widespread in acute critical illness. The study hypothesis was that exposure to corticosteroids influences the mortality and morbidity in acute critical illness.

Methods: This case-control retrospective study was performed in a single multidisciplinary intensive care unit at a tertiary care institution and consisted of 10,285 critically ill patients admitted between 1 January 1999 and 31 December 2004. Demographics, comorbidities, acute illness characteristics including severity measured by Sequential Organ Failure Assessment, concurrent medications, therapeutic interventions and incidence of infections were obtained from electronic medical records, were examined with multiple regression analysis and were adjusted for propensity of corticosteroid exposure. The primary outcome was hospital death, and the secondary outcome was transfer to a care facility at hospital discharge.

Results: Corticosteroid exposure in 2,632 (26%) patients was characterized by younger age, more females, higher Charlson comorbidity and maximal daily Sequential Organ Failure Assessment scores compared with control patients. Corticosteroids potentiated metabolic and neuromuscular sequels of critical illness with increased requirements for diuretics, insulin, protracted weaning from mechanical ventilation, need for tracheostomy and discharge to a care facility. Early exposure to corticosteroids predisposed to recurrent and late onset of polymicrobial and fungal hospital-acquired infections. Corticosteroids increased the risk for death or disability after adjustments for comorbidities and acute illness characteristics.

Conclusion: Corticosteroids increased the risk for death or disability in critical illness. Hospital-acquired infections and metabolic and neuromuscular sequels of critical illness were exacerbated by corticosteroids. Careful appraisal of the indications for use of corticosteroids is necessary to balance the benefits and risks from exposure in acute critical illness.

Introduction

Administration of corticosteroids in a variety of settings in acute critical illness has become widespread. Corticosteroids are used therapeutically for relative adrenal insufficiency as well as for the attenuation of the inflammatory and immune response in the critically ill.[1] Early use of corticosteroids has been recommended in sepsis, acute lung injury, acute respiratory distress syndrome and refractory vasodilatory shock.[2-5] The Corticosteroid Randomization after Significant Head Injury study, a large, international, randomized placebo-controlled trial, was terminated after enrolment of 10,000 patients because of an unexpected rise in the death rate after early administration of corticosteroids.[6] That study report raised concerns with regard to the safety of corticosteroids since, up to that time, they had been liberally administered in a variety of life-threatening illnesses with the intent to improve survival. These concerns were substantiated when we observed, in a previous study, that administration of corticosteroids increased the mortality in vasopressor-dependent critical illness.[7] A similar observation of an unexpected increase in mortality from corticosteroids use was also reported from a randomized controlled trial of corticosteroids in late acute respiratory distress syndrome.[8]
The morbidity related to metabolic, immune and musculoskeletal side-effects of corticosteroids in noncritical illness has been recognized and has created great interest in developing alternative treatments to avoid these complications. In transplantation practice, the therapeutic use of corticosteroids for immunosuppression has decreased because of the introduction of other therapies targeted against specific cytokines including tumour necrosis factor and interleukins or selective lymphocytes calcineurin inhibition.[9,10] New immunosuppression regimes produced superior allograft survival and yet had fewer side effects than traditional high-dose corticosteroids.[11,12] For autoimmune inflammatory disorders and rheumatologic diseases, the use of corticosteroids has also declined because of better treatment options targeting inflammatory cytokines known to influence the progression of these conditions.[13-16]
The use of corticosteroids in noncritical illness has gradually diminished, yet their use in acute critical illness appears to be expanding in relative adrenal insufficiency, sepsis and systemic inflammatory organ injury. This study was designed to address the following questions: What are the frequency and patient characteristics associated with corticosteroid use in acute critical illness? Does the exposure to corticosteroids influence death or disability? What were the mechanisms for the observed effects of corticosteroids in acute critical illness? This study was a retrospective case-control analysis of all admissions to an adult intensive care unit (ICU) with exposure to corticosteroids defining the case group

 Metabolic and Neuromuscular Sequels of Corticosteroids

Corticosteroids exacerbated several metabolic abnormalities induced by acute critical illness. The mineralocorticoid activity of the administered corticosteroids aggravated fluid retention and interstitial oedema in the critically ill. We observed that diuretics were concurrently administered in 65% of patients already on corticosteroids. The simultaneous use of corticosteroids and diuretics to overcome fluid retention was responsible for frequent electrolyte abnormalities in these patients.
Our study observed that the frequency of insulin use for glycaemic control increased with corticosteroid exposure. Administration of insulin with poor glycaemic control could explain the higher mortality related to corticosteroids in our patients. In a previous study, we reported that the use of corticosteroids influenced glucose metabolism, resulting in poor glycaemic control and insulin resistance in the critically ill.[26] The control of blood glucose in acute critical illness has been recommended to improve clinical outcome.[27] Excessive insulin use with poor glycaemic control has been linked to an increased mortality in both medical and surgical critical illness.[26,28]
A variety of neuromyopathy disorders have been attributed to corticosteroid use in critical illness that delayed the functional recovery of survivors.[29,30] The present study observed that corticosteroids delayed weaning from mechanical ventilation and increased the need for tracheostomy. The incidence of care dependency and disability requiring discharge to a care facility was also high in these patients. Global and flaccid muscle weakness affecting the limb musculature, truncal musculature and respiratory musculature related to necrotizing myopathy have been reported with corticosteroid use in critical illness.[31-34] Delayed recovery of respiratory neuromuscular function and extremity neuromuscular function has been documented because peripheral nerve abnormalities and skeletal muscle abnormalities persisted for years, raising concerns for irreversible neuromuscular dysfunction related to corticosteroid use in critical illness.[34,35]
Corticosteroids increased the frequency of postoperative complications in surgical critical illness. Poor or delayed tissue healing, metabolic abnormalities and hospital-acquired infections could explain the vulnerability to complications after surgical procedures in these patients

.Conclusion

Corticosteroids increase the risk for death or disability in acute critical illness. Early exposure to corticosteroids increases the frequency of late hospital acquired infections, polymicrobial infections and fungal infections during the hospital stay. Corticosteroids exacerbate metabolic and neuromuscular sequels of critical illness. Careful appraisal of the indications for use of corticosteroids is necessary to balance the benefits and risks from exposure in acute critical illness

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 Estas son partes del trabajo que ud puede consultar en:

                                                                                             Crit Care. 2006;10(3)

Utilidad de la prueba de troponina T de alta sensibilidad en la detección de rechazo agudo en trasplante cardiaco

 Carmen Muñoz-Esparza, Iris P. Garrido, Rosa Blanco, Teresa Casas, Cristina González-Cánovas, Francisco Pastor-Pérez, Pablo Peñafiel, Alfredo Minguela, Mariano Valdés y Domingo A. Pascual-Figal

                                                                            Rev Esp Cardiol. 2011;64:1109-13.

Resumen

Introducción y objetivos

La detección del rechazo agudo en pacientes trasplantados cardiacos mediante métodos no invasivos representa un reto. La disponibilidad de un nuevo método de alta sensibilidad para la determinación de troponina T podría ayudar a su detección.

Métodos

Estudio case-crossover, en el que cada paciente sirvió como control de sí mismo, mediante la selección de muestras obtenidas en episodios de rechazo agudo tratados (29 casos) y muestras sin rechazo obtenidas inmediatamente antes y/o después (38 controles). La determinación de alta sensibilidad de troponina T se realizó mediante un nuevo test precomercial (Elecsys Troponina T HS).

Resultados

La troponina T fue detectable en todas las muestras: mediana, 0,068 [intervalo intercuartílico, 0,030-0,300] ng/l. Sus concentraciones se correlacionaron con la presión auricular derecha (r=0,37; p=0,002), la fracción aminoterminal del propéptido natriurético cerebral (r=0,67; p<0,001) y el tiempo transcurrido desde el trasplante (r=-0,81; p<0,001). Las concentraciones de troponina T fueron mayores en presencia de rechazo (0,155 frente a 0,047 ng/l; p=0,006). En el análisis operador-receptor, el área bajo la curva fue 0,67 (intervalo de confianza del 95%, 0,53-0,77) y el mejor punto de corte, 0,035 ng/l, que se asoció con mayor riesgo de rechazo (odds ratio=3,7; intervalo de confianza del 95%, 1,2-11,9; p=0,02). Durante los primeros 2 meses, el área bajo la curva aumentó hasta 0,86 (intervalo de confianza del 95%, 0,66-0,97), con un punto de corte óptimo de 1,1 ng/l (sensibilidad, 58% [28-85%]; especificidad, 100% [74-100%]).

Conclusiones

El análisis de alta sensibilidad detectó troponina T en todas las muestras tras el trasplante, en mayor concentración en caso de rechazo agudo, si bien su utilidad en la monitorización se limitaría a servir como apoyo ante la sospecha clínica o histológica, especialmente en los primeros meses

_________________________________________________________________________________ 

INTRODUCCIÓN

A pesar de los avances en la terapia inmunosupresora, un 20-30% de los pacientes sometidos a trasplante cardiaco precisan un incremento del grado de inmunosupresión por rechazo agudo, celular o humoral^{1, 2}. La mortalidad asociada es del 6% en el primer mes y alcanza el 12% al final del primer año³. Actualmente, la biopsia endomiocárdica (BEM) es la herramienta estándar para el diagnóstico de rechazo agudo, a pesar de su carácter invasivo y su baja sensibilidad debida a la importante variabilidad del muestreo y de la interpretación intraobservador e interobservador.

La detección en sangre de troponinas cardiacas es una herramienta habitual en la detección precoz de daño isquémico en los síndromes coronarios agudos. El rechazo agudo también se asocia a necrosis de cardiomiocitos y, por lo tanto, a liberación de troponinas cardiacas^{4, 5}. Sin embargo, la baja sensibilidad de los métodos convencionales para determinar las troponinas cardiacas limita su aplicabilidad clínica en este grupo de pacientes, en los que la liberación inicial es de muy escasa magnitud⁶. En los últimos años se han desarrollado métodos de determinación con alta sensibilidad⁷ que permiten reducir significativamente los límites de detección y podrían permitir su aplicación como una herramienta clínica en la monitorización del rechazo agudo del injerto.

El objetivo de este estudio es evaluar, por primera vez, un nuevo método de alta sensibilidad para la detección de troponina T (hsTnT) en el diagnóstico del rechazo agudo en pacientes con trasplante cardiac

MÉTODOS

 Población y diseño del estudio

Se diseñó un estudio case-crossover, en el que cada paciente sirvió como control de sí mismo, mediante la selección de muestras obtenidas en episodios de rechazo (caso) e inmediatamente antes o después de dicho episodio (control). Entre los años 2000 y 2008, se realizaron 72 trasplantes cardiacos, a los que se practicaron BEM como parte del protocolo habitual de monitorización o por sospecha clínica de rechazo. Las muestras de sangre se obtuvieron inmediatamente antes de cada BEM, dentro del protocolo de la Red de grupos de investigación «Inmunología del trasplante» (Expediente G03/114; Instituto de Salud Carlos III), de las que se obtuvo suero que fue procesado y congelado a -80°C. De dicha población, un total de 29 pacientes (40%) (media de edad, 53±13 años; el 75% varones) presentaron un primer episodio de rechazo agudo durante el primer año, definido como el tratado con metilprednisolona en bolo intravenoso y a dosis ≥ 250mg, según criterios clínicos y/o histológicos de rechazo. Se seleccionaron las muestras obtenidas en el episodio de rechazo (n=29 casos, grupo con rechazo) y las obtenidas en la biopsia sin rechazo realizada inmediatamente antes (n=17) y/o después (n=21) (n=38 controles, grupo sin rechazo). El grado de rechazo histológico fue clasificado en cada biopsia de acuerdo con los criterios de la Sociedad Internacional de Trasplante Cardiaco y Pulmonar⁸. Las características clínicas y de laboratorio en el momento de la biopsia se registraron de manera prospectiva en la historia clínica del paciente, de acuerdo con la práctica clínica habitual para estos pacientes, y se recogió a posteriori para su análisis.

Medidas de laboratorio

Las muestras sufrieron un único ciclo de descongelación para la determinación de troponina T con un inmunoanálisis de electroquimioluminiscencia de alta sensibilidad (Elecsys Troponina T HS), en un analizador Elecsys 2010 (Roche Diagnostics GmbH, Mannheim, Alemania). Dicho test tiene una gama analítica de 0,003-10 ng/ml, un límite de detección de 0,003 ng/ml y un valor de 0,013 ng/ml para el percentil 99 de la población normal (coeficiente de variación para dicho valor, 9%). Este test comercial ha sido validado recientemente y cumple con los requisitos y las recomendaciones de consenso para su uso en el diagnóstico de necrosis miocárdica⁹. La concentración de la fracción aminoterminal del propéptido natriurético cerebral (NT-proBNP) también se midió a través de un inmunoanálisis de electroquimioluminiscencia, utilizando el analizador Elecsys 2010 mencionado anteriormente, cuya imprecisión total es < 3%

Análisis estadístico

Para objetivar diferencias entre grupos con rechazo y sin rechazo, se empleó el test de la t de Student en el caso de variables de distribución normal o la prueba no paramétrica de la U de Mann-Whitney para las variables sin distribución normal. El test de la χ² se empleó para la comparación de variables cualitativas. Para estudiar las posibles influencias en los valores obtenidos por hsTnT, se realizó un análisis de regresión lineal múltiple introduciendo las variables que se correlacionaban significativamente. La utilidad diagnóstica de la hsTnT en la predicción de rechazo celular agudo se evaluó a través del análisis COR (Características Operativas del Receptor), calculando el área bajo la cuva y sus intervalos de confianza (IC) con el método de DeLong¹⁰. El mejor punto de corte para el diagnóstico fue aquel que presentó el producto de especificidad por sensibilidad más elevado. La asociación de riesgo con el rechazo se estudió mediante un análisis de regresión logística en el que se realizó un ajuste por otras variables significativas. Todos los valores de p<0,05 fueron considerados estadísticamente significativos. El análisis estadístico se llevó a cabo mediante el software estadístico MedCalc 11.3.0 (MedCalc Software, Mariakerke, Bélgica) para el análisis COR y PASW 18.0 (SPSS Inc., Chicago, Illinois, Estados Unidos) para los demás anális

RESULTADOS

Las características clínicas y bioquímicas se muestran en la Tabla 1, según la presencia o ausencia de rechazo. Para la población total, la troponina T fue detectable en todas las muestras (100%), con una mediana de 0,068 (0,030-0,300) ng/ml, y se encontraron concentraciones significativamente mayores en los pacientes con rechazo. Al estratificar a la población en función de terciles de troponina T, también se observó una asociación con mayor prevalencia de rechazo (p=0,02): 23% (< 0,035ng/ml), 48% (0,035-0,176 ng/ml) y 59% (> 0,176 ng/ml). La Tabla 2 muestra las variables clínicas que se correlacionaron con los valores de troponina T; tras el ajuste de regresión lineal múltiple, el tiempo transcurrido desde el trasplante, la presión auricular derecha y la concentración de NT-proBNP fueron sus principales determinantes. No se encontró correlación entre las concentraciones de troponina T y el grado histológico de rechazo (p > 0,5).

Tabla 1. Características basales de las biopsias endomiocárdicas según haya o no asociación con rechazo agudo

Valores expresados como media±desviación estándar o mediana [intervalo intercuartílico].
FEVI: fracción de eyección del ventrículo izquierdo; NT-proBNP: fracción aminoterminal del propéptido natriurético cerebral; VD: ventrículo derecho.

Tabla 2. Variables relacionadas con la concentración de troponina T en el análisis de regresión lineal

NT-proBNP: fracción aminoterminal del propéptido natriurético cerebral.

El análisis COR mostró un área bajo la curva de 0,67 (IC del 95%, 0,53-0,77) para la presencia de rechazo; el punto óptimo de corte fue 0,035 ng/ml, con sensibilidad del 83% (IC del 95%, 64-94%), especificidad del 45% (IC del 95%, 29-62%), valor predictivo positivo del 56% y valor predictivo negativo del 77%. En un modelo multivariable, se asoció a un mayor riesgo de rechazo (p=0,02; odds ratio [OR]=3,7; IC del 95%, 1,2-11,9) tras el ajuste por el tiempo de evolución, las presiones derechas y el NT-proBNP. Cuando el análisis COR se restringió a los primeros 2 meses (12 muestras con rechazo y 12 controles sin rechazo), se observó un incremento del área bajo la curva hasta 0,86 (IC del 95%, 0,66-0,97), y el punto de corte óptimo se elevó a 1,10 ng/mL, con sensibilidad del 58% (IC del 95%, 28-85%), especificidad del 100% (IC del 95%, 74-100%), valor predictivo positivo del 100% y negativo del 66%.

DISCUSIÓN

Dadas las limitaciones de la BEM, se han estudiado múltiples alternativas no invasivas para la detección del rechazo agudo cardiaco^{5, 8, 11, 12, 13, 14}. Entre ellas, la determinación de troponinas cardiacas con pruebas convencionales también se ha evaluado, con hallazgos discordantes. Así, en algunas series de biopsias, sus concentraciones han mostrado correlación con el grado histológico de rechazo^{5, 6}, mientras que otros trabajos no han encontrado esta asociación^{11, 12, 15, 16}. Sin embargo, todos esos trabajos coinciden en mostrar escasa sensibilidad y bajo valor predictivo positivo.

El trabajo aquí presentado muestra, en primer lugar, que con el uso de un análisis de alta sensibilidad la troponina T fue detectable en todas las muestras con y sin rechazo. Con tests convencionales, un 54% de los pacientes presentan concentraciones persistentemente detectables. Este hallazgo concuerda con la elevada sensibilidad que estos nuevos tests han mostrado en pacientes con sospecha de enfermedad coronaria^{17, 18}. Además, las concentraciones fueron significativamente mayores en los casos de rechazo que precisaron tratamiento con esteroides intravenosos, con base en hallazgos biópsicos o clínicos. Sin embargo, el área bajo la curva fue relativamente baja, lo que podría explicarse por la importante influencia del tiempo tras el trasplante (r=-0,8). Por otro lado, sólo la sensibilidad y el valor predictivo negativo elevados pueden permitir que se evite la necesidad de biopsia en la monitorización del rechazo cardiaco, y en este sentido, los valores mostrados por la hsTnT fueron relativamente bajos. Por lo tanto, la monitorización mediante hsTnT no evita la necesidad de BEM, si bien la asociación positiva con el rechazo que encontramos en este estudio indica su uso en apoyo de la sospecha clínica o biópsica. En este sentido, su capacidad diagnóstica mejoró en el periodo precoz, en el que valores elevados de troponina se asociaron con un elevado valor predictivo positivo (100%), por lo que la ausencia de descenso o la elevación de su concentración postrasplante por encima de 1,10 ng/mL podría ayudar a sospechar la presencia de rechazo agudo durante los primeros meses de evolución.

Un aspecto de interés es que en nuestra población, no encontramos una asociación con la gradación histológica, como ya se había descrito en otros estudios con pruebas convencionales^{11, 12, 15, 16}. Este hecho pone de manifiesto la imperfección de usar la histología de las biopsias endomiocardicas como única herramienta patrón. De hecho, los cambios moleculares de rechazo se correlacionan mejor con los hallazgos clínicos que con las lesiones histológicas, tal y como han mostrado Mengel et al¹⁹ recientemente. En nuestro análisis, la correlación de la hsTnT con las presiones de llenado y el NT-proBNP indica también una correlación clínica con variables hemodinámicas que se afectan por la presencia de rechazo con repercusión clínica^{20, 21}.

Este estudio está limitado por su carácter observacional y el pequeño número de muestras obtenidas en diferentes periodos de tiempo; sin embargo, esto se debe a que el trasplante es un procedimiento infrecuente y los episodios de rechazo son un evento imprevisible en la evolución de estos pacientes. La principal fortaleza de este estudio es que evalúa por primera vez la detección de troponinas con un test de alta sensibilidad y puede servir para aumentar el conocimiento en esta área y ayudar al diseño de nuevos estudios centrados en la búsqueda de marcadores no invasivos de rechazo. En cualquier caso, nuevos estudios con diseño prospectivo se hacen necesarios para definir mejor el papel de la hsTnT con o sin otros marcadores biológicos en la monitorización del rechazo tras el trasplante cardiaco.

CONCLUSIONES

Los hallazgos muestran que, usando un test de alta sensibilidad, la troponina T es medible en todos los pacientes tras el trasplante y se encuentra en mayores concentraciones en presencia de rechazo agudo. Además, indica que la persistencia de valores elevados en el periodo precoz se asocia a un mayor riesgo de rechazo, si bien su uso en la monitorización continua debe ser individualizado y siempre como parámetro de apoyo de la sospecha clínica y/o histológica.

CONFLICTO DE INTERESES

El Dr. Domingo Pascual-Figal ha recibido becas de investigación de Roche Diagnostics.

Agradecimientos

Los reactivos para la determinación mediante hsTnT fueron donados por Roche Diagnostics.

Recibido 29 Marzo 2011
Aceptado 19 Junio 2011

Autor para correspondencia: Servicio de Cardiología, Hospital Universitario Virgen de la Arrixaca, Ctra. Madrid-Cartagena s/n, 30120 Murcia, España. dapascual@servicam.com

Bibliografía

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2.Almenar L, Segovia J, Crespo-Leiro MG, Palomo J, Arizón JM, González-Vílchez F, et-al. Registro Español de Trasplante Cardiaco. XXI Informe Oficial de la Sección de Insuficiencia Cardiaca y Trasplante Cardiaco de la Sociedad Española de Cardiología (1984-2009). Rev Esp Cardiol. 2010; 63:1317-28.

3.Taylor DO, Stehlik J, Edwards LB, Aurora P, Christie JD, Dobbels F, et-al. Registry of the International Society for Heart and Lung Transplantation: Twenty-sixth Official Adult Heart Transplant Report-2009. J Heart Lung Transplant. 2009; 28:1007-22.

4.Zimmermann R, Baki S, Dengler TJ, Ring GH, Remppis A, Lange R, et-al. Troponin T release after heart transplantation. Br Heart J. 1993; 69:395-8.

5.Dengler TJ, Zimmermann R, Braun K, Müller-Bardorff M, Zehelein J, Sack FU, et-al. Elevated serum concentrations of cardiac troponin T in acute allograft rejection after human heart transplantation. J Am Coll Cardiol. 1998; 32:405-12.

6.Chance JJ, Segal JB, Wallerson G, Kasper E, Hruban RH, Kickler TS, et-al. Cardiac troponin T and C-reactive protein as markers of acute cardiac allograft rejection. Clin Chim Acta. 2001; 312:31-9.

7.Jaffe AS, Ordóñez-Llanos J. Troponinas ultrasensibles en el dolor torácico y los síndromes coronarios agudos. ¿Un paso hacia delante?. Rev Esp Cardiol. 2010; 63:763-9.

8.Stewart S, Winters GL, Fishbein MC, Tazelaar HD, Kobashigawa J, Abrams J, et-al. Revision of the 1990 working formulation for the standardization of nomenclature in the diagnosis of heart rejection. J Heart Lung Transplant. 2005; 24:1710-20.

9.Giannitsis E, Kurz K, Hallermayer K, Jarausch J, Jaffe AS, Katus HA. Analytical validation of a high-sensitivity cardiac troponin T assay. Clin Chem. 2010; 56:254-61.

10.DeLong ER, DeLong DM, Clarke-Pearson DL. Comparing the areas under two or more correlated receiver operating characteristic curves: a nonparametric approach. Biometrics. 1988; 44:837-45.

11.Mullen JC, Bentley MJ, Scherr KD, Chorney SG, Burton NI, Tymchak WJ, et-al. Troponin T and I are not reliable markers of cardiac transplant rejection. Eur J Cardiothorac Surg. 2002; 22:233-7.

12.Alexis JD, Lao CD, Selter JG, Courtney MC, Correa DK, Lansman SL, et-al. Cardiac troponin T: a noninvasive marker for heart transplant rejection?. J Heart Lung Transplant. 1998; 17:395-8.

13.Avello N, Molina BD, Llorente E, Bernardo MJ, Prieto B, Alvarez FV. N-terminal pro-brain natriuretic peptide as a potential non-invasive marker of cardiac transplantation rejection. Ann Clin Biochem. 2007; 44:182-8.

14.Balduini A, Campana C, Ceresa M, Arbustini E, Bosoni T, Serio A, et-al. Utility of biochemical markers in the follow-up of heart transplant recipients. Transplant Proc. 2003; 35:3075-7.

15.Walpoth BH, Celik B, Printzen G, Peheim E, Colombo JP, Schaffner T, et-al. Assessment of troponin-T for detection of clinical cardiac rejection. Transpl Int. 1998; 11(Suppl 1):S502-7.

16.Wang CW, Steinhubl SR, Castellani WJ, Van Lente F, Miller DP, James KB, et-al. Inability of serum myocyte death markers to predict acute cardiac allograft rejection. Transplantation. 1996; 62:1938-41.

17.Reichlin T, Hochholzer W, Bassetti S, Steuer S, Stelzig C, Hartwiger S, et-al. Early diagnosis of myocardial infarction with sensitive cardiac troponin assays. N Engl J Med. 2009; 361:858-67.

18.Omland T, De Lemos JA, Sabatine MS, Christophi CA, Rice MM, Jablonski KA, et-al. Prevention of Events with Angiotensin Converting Enzyme Inhibition (PEACE) trial investigators. A sensitive cardiac troponin T assay in stable coronary artery disease. N Engl J Med. 2009; 361:2538-47.

19.Mengel M, Sis B, Kim D, Chang J, Famulski KS, Hidalgo LG, et-al. The molecular phenotype of heart transplant biopsies: relationship to histopathological and clinical variables. Am J Transplant. 2010; 10:2105-15.

20.Kirchhoff WCh , Gradaus R, Stypmann J, Deng MC, Tian TD, Scheld HH, et-al. Vasoactive peptides during long-term follow-up of patients after cardiac transplantation. J Heart Lung Transplant. 2004;23:284-8. 

21.Hervás I, Arnau MA, Almenar L, Pérez-Pastor JL, Chirivella M, Osca J, et-al. Ventricular natriuretic peptide (BNP) in heart transplantation: BNP correlation with endomyocardial biopsy, laboratory and hemodynamic measures. Lab Invest. 2004; 84:138-45.

Se presenta una búsqueda de trabajos (reviews) sobre Alcalosis Metabólica 

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Mayo Clin Proc. 2009 Mar;84(3):261-7.

 Milk-alkali syndrome.

 Medarov BI

 Milk-alkali syndrome (MAS) consists of hypercalcemia, various degrees of renal failure, and metabolic alkalosis due to ingestion of large amounts of calcium and absorbable alkali. This syndrome was first identified after medical treatment of peptic ulcer disease with milk and alkali was widely adopted at the beginning of the 20th century. With the introduction of histamine2 blockers and proton pump inhibitors, the occurrence of MAS became rare; however, a resurgence of MAS has been witnessed because of the wide availability and increasing use of calcium carbonate, mostly for osteoporosis prevention. The aim of this review was to determine the incidence, pathogenesis, histologic findings, diagnosis, and clinical course of MAS. A MEDLINE search was performed with the keyword milk-alkali syndrome using the PubMed search engine. All relevant English language articles were reviewed. The exact pathomechanism of MAS remains uncertain, but a unique interplay between hypercalcemia and alkalosis in the kidneys seems to lead to a self-reinforcing cycle, resulting in the clinical picture of MAS. Treatment is supportive and involves hydration and withdrawal of the offending agents. Physicians and the public need to be aware of the potential adverse effects of ingesting excessive amounts of calcium carbonate.

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 J Indian Med Assoc. 2006 Nov;104(11):630-4, 636.

Diagnosis and management of metabolic alkalosis.

Pahari DK, Kazmi W, Raman G, Biswas S.

Elevated pH and elevated plasma bicarbonate level above normal characterise metabolic alkalosis. When bicarbonate is elevated pCO2 must also be elevated to maintain pH to its normal range. Therefore with metabolic alkalosis, the compensation is to decrease alveolar ventilation, and increase pCO2. The causes of metabolic alkalosis are gastro-intestinal hydrogen and chloride loss and due to renal cause. For metabolic alkalosis to continue both generation and maintenance of high levels of bicarbonate are necessary. The diagnosis of metabolic alkalosis is established by noting pH, serum bicarbonate (elevated) and pCO2 (compensatory) elevation. To establish the causes it is necessary to determine intravascular volume, supine and standing blood pressure and renin angiotension alolosterone axis. In chloride responsive alkalosis in which the conditions are extracellular volume depletion, hypokalaemia and hypochloraemia correction of intravascular volume with sodium chloride is needed. In severe metabolic alkalosis of any cause dilute hydrochloric acid (0.1 N HCl) may be infused intravenously but haemolysis may be a complication. In emergency situation with severe hypokalaemia dialysis with higher K+, Cl- and low HCO3- bath will be appropriate.

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Semin Nephrol. 2006 Nov;26(6):404-21.

Metabolic alkalosis, bedside and bench

Laski ME, Sabatini S.

Although significant contributions to the understanding of metabolic alkalosis have been made recently, much of our knowledge rests on data from clearance studies performed in humans and animals many years ago. This article reviews the contributions of these studies, as well as more recent work relating to the control of renal acid-base transport by mineralocorticoid hormones, angiotensin, endothelin, nitric oxide, and potassium balance. Finally, clinical aspects of metabolic alkalosis are considered.

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 J Nephrol. 2006 Mar-Apr;19 Suppl 9:S86-96.

 Metabolic alkalosis.

 Khanna A, Kurtzman NA.

 Metabolic alkalosis is a primary pathophysiologic event characterized by the gain of bicarbonate or the loss of nonvolatile acid from extracellular fluid. The kidney preserves normal acid-base balance by two mechanisms: bicarbonate reclamation mainly in the proximal tubule and bicarbonate generation predominantly in the distal nephron. Bicarbonate reclamation is mediated mainly by a Na-H antiporter and to a smaller extent by the H-ATPase. The principal factors affecting HCO 3 reabsorption include effective arterial blood volume, glomerular filtration rate, chloride, and potassium. Bicarbonate regeneration is primarily affected by distal Na delivery and reabsorption, aldosterone, arterial pH, and arterial pCO2. To generate metabolic alkalosis, either a gain of base or a loss of acid, must occur. The loss of acid may be via the GI tract or by the kidney. Excess base may be gained by oral or parenteral HCO 3 administration or by lactate, acetate, or citrate administration. Factors that help maintain metabolic alkalosis include decreased glomerular filtration rate (GFR), volume contraction, hypokalemia, hypochloremia, and aldosterone excess. Clinical states associated with metabolic alkalosis are vomiting, mineralocorticoid excess, the adrenogenital syndrome, licorice ingestion, diuretic administration, and Bartter's and Gitelma's Syndromes. The effects of metabolic alkalosis on the body are varied and include effects on the central nervous system, myocardium, skeletal muscle, and the liver. Treatment of this disorder is simple, once the pathophysiology of the cause is delineated. Therapy consists of reversing the contributory factors promoting alkalosis and in severe cases, administration of carbonic anhydrase inhibitors, acid infusion, and low bicarbonate dialysis.

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 Am J Med Sci. 2001 Dec;322(6):316-32.

 Inherited primary renal tubular hypokalemic alkalosis: a review of Gitelman and Bartter syndromes.

 Shaer AJ.

 Inherited hypokalemic metabolic alkalosis, or Bartter syndrome, comprises several closely related disorders of renal tubular electrolyte transport. Recent advances in the field of molecular genetics have demonstrated that there are four genetically distinct abnormalities, which result from mutations in renal electrolyte transporters and channels. Neonatal Bartter syndrome affects neonates and is characterized by polyhydramnios, premature delivery, severe electrolyte derangements, growth retardation, and hypercalciuria leading to nephrocalcinosis. It may be caused by a mutation in the gene encoding the Na-K-2Cl cotransporter (NKCC2) or the outwardly rectifying potassium channel (ROMK), a regulator of NKCC2. Classic Bartter syndrome is due to a mutation in the gene encoding the chloride channel (CLCNKB), also a regulator of NKCC2, and typically presents in infancy or early childhood with failure to thrive. Nephrocalcinosis is typically absent despite hypercalciuria. The hypocalciuric, hypomagnesemic variant of Bartter syndrome (Gitelman syndrome), presents in early adulthood with predominantly musculoskeletal symptoms and is due to mutations in the gene encoding the Na-Cl cotransporter (NCCT). Even though our understanding of these disorders has been greatly advanced by these discoveries, the pathophysiology remains to be completely defined. Genotype-phenotype correlations among the four disorders are quite variable and continue to be studied. A comprehensive review of Bartter and Gitelman syndromes will be provided here.

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 Respir Care. 2001 Apr;46(4):354-65.

 Metabolic alkalosis.

 Khanna A, Kurtzman NA

 Metabolic alkalosis is a primary pathophysiologic event characterized by the gain of bicarbonate or the loss of nonvolatile acid from extracellular fluid. The kidney preserves normal acid-base balance by two mechanisms: bicarbonate reclamation, mainly in the proximal tubule, and bicarbonate generation, predominantly in the distal nephron. Bicarbonate reclamation is mediated mainly by a Na(+)-H(+) antiporter and to a smaller extent by the H(+)-ATPase (adenosine triphosphate-ase). The principal factors affecting HCO3(-) reabsorption include effective arterial blood volume, glomerular filtration rate, chloride, and potassium. Bicarbonate regeneration is primarily affected by distal Na(+) delivery and reabsorption, aldosterone, arterial pH, and arterial partial pressure of carbon dioxide. To generate metabolic alkalosis, either a gain of base or a loss of acid must occur. The loss of acid may be via the gastrointestinal tract or via the kidney. Excess base may be gained by oral or parenteral HCO3(-) administration or by lactate, acetate, or citrate administration. Factors that help maintain metabolic alkalosis include decreased glomerular filtration rate, volume contraction, hypokalemia, hypochloremia, and aldosterone excess. Clinical states associated with metabolic alkalosis are vomiting, mineralocorticoid excess, the adrenogenital syndrome, licorice ingestion, diuretic administration, and Bartter's and Gitelman's syndromes. The effects of metabolic alkalosis on the body are variable and include effects on the central nervous system, myocardium, skeletal muscle, and liver. Treatment of this disorder is simple, once the pathophysiology of the cause is delineated. Therapy consists of reversing the contributory factors that are promoting the alkalosis and, in severe cases, administration of carbonic anhydrase inhibitors, acid infusion, and low bicarbonate dialysis.

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 Compr Ther. 2000 Summer;26(2):114-20.

 Hypokalemia and metabolic alkalosis: algorithms for combined clinical problem solving.

 Bartholow C, Whittier FC, Rutecki GW

 This article reviews an approach to patients with hypokalemia and metabolic alkalosis using the information obtained from spot urine chloride values, blood pressure determinations, and renin and aldosterone measurements in order to simplify clinical problem solving

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 Crit Rev Clin Lab Sci. 1999 Oct;36(5):497-510.

 Metabolic alkalosis in the critically ill.

 Webster NR, Kulkarni V.

 Metabolic alkalosis is the commonest form of acid-base disorder seen in critically ill patients. Although the effects of acidosis have long been known, those of severe metabolic alkalosis are only slowly being recognized. Metabolic alkalosis is itself associated with an increased mortality and a knowledge of the causative factors and treatment options is important. In one study, around 50% of general surgical patients developed postoperative metabolic alkalosis, whereas other acid-base disturbances were uncommon. Metabolic alkalosis results from an accumulation of alkali or a loss of acid. Clinical signs are nonspecific but dehydration may be prominent because of a contraction of the extracellular fluid volume due to loss of chloride. Metabolic alkalosis leads to hypoventilation in patients both with and without lung disease, although in the latter, the effect is relatively transient. In patients with chronic obstructive lung disease, however, the development of metabolic alkalosis leads to prolonged hypoventilation and the establishment of a mixed acid-base disorder that may cause difficulty in weaning in the ventilated patient. This is an often forgotten cause of prolonged stay in the intensive care unit with consequent cost and morbidity implications

Predictive Value of Procalcitonin Decrease in Patients with Severe Sepsis: A Prospective Observational Study

                                              Sari Karlsson; Milja Heikkinen; Ville Pettilä; Seija Alila; Sari Väisänen;
                                              Kari Pulkki; Elina Kolho; Esko Ruokonen

                                             Crit Care. 2010;14(6):R205 

Abstract and Introduction

Introduction: This prospective study investigated the predictive value of procalcitonin (PCT) for survival in 242 adult patients with severe sepsis and septic shock treated in intensive care.
Methods: PCT was analyzed from blood samples of all patients at baseline, and 155 patients 72 hours later.
Results: The median PCT serum concentration on day 0 was 5.0 ng/ml (interquartile range (IQR) 1.0 and 20.1 ng/ml) and 1.3 ng/ml (IQR 0.5 and 5.8 ng/ml) 72 hours later. Hospital mortality was 25.6% (62/242). Median PCT concentrations in patients with community-acquired infections were higher than with nosocomial infections (P = 0.001). Blood cultures were positive in 28.5% of patients (n = 69), and severe sepsis with positive blood cultures was associated with higher PCT levels than with negative cultures (P = < 0.001). Patients with septic shock had higher PCT concentrations than patients without (P = 0.02). PCT concentrations did not differ between hospital survivors and nonsurvivors (P = 0.64 and P = 0.99, respectively), but mortality was lower in patients whose PCT concentration decreased > 50% (by 72 hours) compared to those with a < 50% decrease (12.2% vs. 29.8%, P = 0.007).
Conclusions: PCT concentrations were higher in more severe forms of severe sepsis, but a substantial concentration decrease was more important for survival than absolute values

Introduction

Because promptly administered antimicrobial and early goal-directed treatment has been shown to improve outcome in patients with severe sepsis,^[1,2] early recognition of infection as a cause of critical illness is of major importance. Various biomarkers, such as C-reactive protein (CRP), interleukin-6 (IL-6), and triggering receptor expressed on myeloid cells-1 (TREM-1), have been studied as a means of detecting infection as a cause of systemic inflammation response syndrome, but none has been shown to be used reliably to diagnose sepsis.^[3] In addition, CRP and other biomarkers have not been shown to detect patients with a high risk of poor outcome.^[4]
Procalcitonin (PCT) is a 116-amino acid prohormone of calcitonin^[5] that is found in the bloodstream without changes in the total amount of calcitonin.^[6] The production of PCT is stimulated by inflammatory cytokines, such as tumor necrosis factor-alpha and IL-6.^[7] PCT concentrations increase after bacterial infection but also in noninfectious conditions with systemic inflammation, such as multiple trauma, cardiogenic shock, induction of hypothermia after cardiac arrest, and drug sensitivity reactions.^[8-11] PCT concentrations are also elevated after major surgery.^[12] However, bacterial infections increase the expression of the PCT-producing CALC-1 gene in multiple extrathyroid tissues throughout the body.^[13]
Patients without infection and inflammation usually have low serum PCT concentrations (< 0.05 ng/mL). In patients with severe sepsis or septic shock, PCT concentrations may increase significantly (up to 1,000 ng/mL).^[5] The cutoff value for sepsis has been set at 0.44 to 1.0 ng/mL in different studies.^[14,15] PCT concentrations have been used to differentiate noninfected patients from infected patients in prospective clinical studies, and higher mortality has been associated with patients who have increasing or persistently high PCT concentrations.^[16] Recent studies concerning PCT have focused on patients with suspected or verified bacterial infections, and the duration of antibiotic treatment was guided by decreasing PCT concentrations.^[17-19] Reduced antibiotic administration without increased adverse outcomes has been shown in patients with lower respiratory tract infections (LRTIs),^[18] medical intensive care unit (ICU) patients,^[19] and patients with severe sepsis and septic shock.^[20]
Meta-analyses of PCT have produced conflicting results. One study concluded that PCT measurement cannot differentiate sepsis reliably from other causes of systemic inflammatory response syndrome and should not be used widely in a critical care setting.^[21] In contrast, another study regarded PCT as superior to CRP measurement and concluded that PCT should be used to diagnose sepsis in ICUs.^[22] Differences in the case mix may contribute to the varying results in critical care settings: on admission to the hospital or ICU, patients are at different phases in the course of their sepsis; preceding antibiotic treatment may be absent, ineffective,^[23] or delayed;^[1] and in postoperative patients, the type of surgery may influence PCT concentrations.^[24]
In the present study, we measured PCT concentrations twice in adult ICU patients with clinically diagnosed severe sepsis in the first 3 days after diagnosis. We evaluated PCT concentrations and the type of organ dysfunction, the type of infection (blood culture-positive, community-acquired, or nosocomial), and the predictive value for outcome of the first PCT concentration and the decrease in PCT after treatment in this large population of patients with severe sepsis.

Materials and Methods

Patient Selection

This study was part of the Finnsepsis study, a prospective observational cohort study of incidence and outcome of severe sepsis in Finland.^[25] All adult consecutive ICU admission episodes (4,500) in 24 ICUs were screened for severe sepsis in a 4-month period (from 1 November 2004 to 28 February 2005). Patients were eligible if they fulfilled the American College of Chest Physicians/Society of Critical Care Medicine (ACCP/SCCM) criteria for severe sepsis or septic shock.^[26] Study entry (day 0) was the time when these criteria were first met. Consent from the ethics committee was granted from each hospital. All patients or their next of kin gave written consent for the study. APACHE II (Acute Physiology and Chronic Health Evaluation II) score and SAPS II (Simplified Acute Physiology Score II),^[27,28] organ dysfunction evaluated with SOFA (Sequential Organ Failure Assessment) score, maximum SOFA scores,^[29,30] and ICU and hospital mortalities were recorded. Septic shock was defined as cardiovascular SOFA score 4, and acute kidney injury was defined as renal SOFA score 3 or 4. Severe sepsis was defined as community-acquired if the infection was present or suspected at hospital admission or less than 48 hours thereafter and was defined as nosocomial if the infection was diagnosed at least 48 hours after hospital admission. Blood CRP concentrations were analyzed as daily routine samples in each participating hospital. Blood cultures were drawn when clinically indicated and were analyzed locally.

Blood Samples

Arterial blood samples for PCT analyses were drawn after informed consent within 24 hours of study entry (day 0) and 72 hours thereafter. The reason for exclusion was failure to obtain consent. Blood for serum samples was collected, and the samples were prepared within 60 minutes of sampling. The samples were stored at -80°C for later analysis. Serum PCT levels were measured with the Cobas 6000 analyzer (Hitachi High-Technologies Corporation, Tokyo, Japan). Analyzer reagents (Elecsys B·R·A·H·M·S PCT assay) were developed in collaboration with B·R·A·H·M·S Aktiengesellschaft (Hennigsdorf, Germany) and Roche Diagnostics (Mannheim, Germany). The functional assay sensitivity (that is, the lowest concentration that can be quantified with a between-run imprecision of 20%) met the Roche Diagnostics specification of 0.06 ng/mL. The respective within- and between-day coefficients of variation for PCT analyses were 1.4% and 3.0% for 0.46 ng/mL PCT and 1.1% and 2.6% for 9.4 ng/mL PCT.

Statistical Analyses

Data are presented as median and interquartile range (IQR) (25th to 75th percentiles), absolute value and percentage, or mean ± standard deviation. The nonparametric data between survivors and nonsurvivors were compared with the Mann-Whitney U test, and categorical variables were compared with the chi-square test. PCT kinetics are expressed as delta PCT (ΔPCT) concentrations. ΔPCT was calculated as the difference between concentrations on day 0 and 72 hours (day 0 to 72 hours). ΔPCT was positive with decreasing concentrations and negative with increasing concentrations. The level of change between the two samples (for example, greater than 50%) was calculated as a proportion of ΔPCT/PCT on day 0. The sensitivity, specificity, and positive likelihood ratio for different PCT cutoff levels were calculated. To determine the prognostic accuracy of PCT and CRP on both time points, receiver operating characteristic (ROC) curves were constructed and the areas under the curve (AUCs) were calculated with 95% confidence intervals (CIs). A P value of less than 0.05 was considered to be statistically significant in all tests. The analyses were performed using SPSS 17.0 software (SPSS Inc., Chicago, IL, USA).

Results

Informed consent and blood samples for the PCT analyses were obtained from 242 out of 470 patients (51.2%) of the Finnsepsis study population. Two hundred forty-two samples were obtained at baseline (day 0); of these, 155 samples were available 72 hours later. Fourteen patients died and 13 were discharged from the ICU before the second sample was obtained. Owing to logistical reasons, an additional 59 samples were not available.
The flowchart of the study is presented in Figure 1. The patients were divided by the type of infection and the cutoff concentration for PCT to detect unlikely sepsis (< 0.5 ng/mL) in semiquantitative PCT measurements (PCT-Q test).^[31] Age, gender, APACHE II score, SAPS II, maximum SOFA score, ICU mortalities, and hospital mortalities did not differ from the Finnsepsis patients who did not have PCT analyses (P = 0.75, 0.63, 0.58, 0.35, 0.22, 024, and 0.18, respectively). The infection and mortality data of patients with community-acquired or nosocomial severe sepsis are presented in Table 1. Mortality in patients with positive blood cultures did not differ from patients with blood culture-negative infections (26.1% and 25.4%, respectively; P = 0.92). Hospital mortality of patients with severe septic shock (cardiovascular SOFA score 4) was higher than that of patients with less severe or absent cardiovascular failure (31.6% versus 22.4%, P = 0.015).

Procalcitonin Concentrations

The median PCT concentrations in patients with severe sepsis are presented in Table 2. On day 0, the range varied from 0.02 to 261.9 ng/mL, and after 72 hours, the range varied from 0.03 to 439 ng/mL. PCT concentrations did not differ between hospital survivors and nonsurvivors at either time point (P = 0.64 and P = 0.99 for day 0 and 72 hours, respectively). The ROC curves for day-0 and 72-hour PCT concentrations and mortality showed AUCs of 0.42 (95% CI 0.31 to 0.54, P = 0.19) and 0.50 (95% CI 0.38 to 0.62, P = 0.99), respectively. High PCT concentrations (PCT > 10 ng/mL) on day 0 or 72 hours did not predict mortality; AUCs were 0.58 (CI 0.43 to 0.73, P = 0.25) and 0.36 (CI 0.09 to 0.62, P = 0.33), respectively.

Procalcitonin and Type of Infection

The median PCT concentrations on day 0 and after 72 hours in patients with community-acquired infections were higher than in patients with nosocomial infections (P = 0.001 and P = 0.003, respectively) (Figure 2). Blood cultures were drawn from 160 out of 242 patients (66%) and were positive in 69 out of 242 (28.5%). PCT concentrations in relation to blood cultures and community-acquired or nosocomial infections are presented in Table 2. PCT concentrations were higher in patients with positive blood cultures at both time points (P < 0.001 and P < 0.001, respectively). The ROC curves for day-0 and 72-hour PCT concentrations predicted blood culture-positive infections, with AUCs of 0.76 (95% CI 0.66 to 0.86, P < 0.001) and 0.74 (95% CI 0.64 to 0.84, P < 0.001) (Figure 3). The cutoff PCT concentration for blood culture-positive infection with 90% sensitivity (95% CI 83% to 97%) was 1.2 ng/mL. The positive likelihood ratio was 1.4 (95% CI 1.2 to 1.6). The cutoff PCT concentration of 10 ng/mL had 62% (95% CI 51% to 74%) sensitivity and 73% (95% CI 63% to 82%) specificity with a positive likelihood ratio of 2.3 (95% CI 1.5 to 3.3) for positive blood culture. PCT of greater than 20 ng/mL had 85% specificity (95% CI 77% to 92%), and the positive likelihood ratio was 3 (95% CI 1.7 to 5.2).
Thirty-six patients with clinically diagnosed severe sepsis and low PCT concentrations ('sepsis unlikely') had median PCT concentrations of 0.17 ng/mL (IQR 0.93 and 0.27 ng/mL) on day 0 and 0.13 ng/mL (IQR 0.08 and 0.22 ng/mL). Only one patient had a strongly increasing PCT of 17.88 ng/mL after 72 hours. The patient had an intra-abdominal infection. Nosocomial infection was found in 53% (19/36) of these patients, and the sources of infection were the lungs in 44% (16/36) and intra-abdominal in 31% (11/36). One patient had a blood culture-positive infection, and 14 other patients had significant microbial growths.

Procalcitonin and Organ Dysfunction

Patients with septic shock or acute kidney injury also had significantly higher PCT concentrations on day 0 compared with patients with milder or absent organ dysfunction (P = 0.020 and P = 0.027, respectively) (Table 2). When patients with two available PCT samples (n = 155) were divided into two groups according to decreasing PCT (n = 130) or increasing PCT (n = 25), no significant differences were found in organ dysfunction (P = 0.58).

Changes in Procalcitonin Concentrations

We analyzed the difference in PCT concentrations on day 0 and 72 hours (ΔPCT) for the 155 patients with two blood samples available. The PCT concentration decreased in 130 patients and increased in the remaining 25 patients, but the change in PCT concentration was not associated with mortality (P = 0.25). Of the patients with decreasing PCT concentrations, 66% (86/130) had community-acquired infections and 34% (44/130) had nosocomial infections (P = 0.014).
When the decreases in PCT concentrations were divided into arbitrary classes from greater than 50% to greater than 90%, a substantial decrease in PCT concentration of greater than 50% between the first and second time points had an effect on hospital survival (Figure 4). The hospital mortality in patients with a greater than 50% decrease in PCT was 12.2% (12/98) compared with 29.8% (17/57) in patients with a less than 50% decrease (P = 0.007). Community-acquired infections (69.8%, 67/96) were associated with a greater than 50% decrease more often than nosocomial infections were (52.5%, 31/59; P = 0.031). In patients with community-acquired severe sepsis, a greater than 50% decrease was associated with better outcome (62.5% survivors) compared with patients with less than 50% decrease (19.8% survivors, P = 0.05). However, this association was not present for patients with nosocomial severe sepsis (P = 0.40). In all patients with available ΔPCT (n = 155), a greater than 50% PCT decrease showed a poor AUC of 0.52 (95% CI 0.36 to 0.68). The PCT decrease of greater than 50% was not independently associated with in-hospital mortality (P = 0.47, odds ratio 0.99, 95% CI 0.96 to 1.02) either.

C-reactive Protein Measurements

The median CRP concentrations of this study population were 197 mg/L (104 and 294 mg/L) on day 0 and 149 mg/L (76 and 201 mg/L) after 72 hours. Patients with positive blood cultures had higher day-0 CRP concentrations compared with patients with negative cultures (244 mg/L [131 to 325 mg/mL] and 187 mg/L [89 to 273 mg/L], respectively; P = 0.016). For patients with decreasing or increasing PCT concentrations, the CRP levels did not differ significantly on day 0 or after 72 hours (P = 0.138 and P = 0.552, respectively). CRP concentrations were not associated with the severity of cardiovascular dysfunction (P = 0.35 and P = 0.11 for day 0 and 72 hours, respectively). The ROC curves for day-0 and 72-hour CRP concentrations and mortality showed inadequate AUCs of 0.52 (95% CI 0.46 to 0.58) and 0.59 (95% CI 0.53 to 0.65), respectively (P = 0.99).

Discussion

PCT concentrations varied largely among individual ICU patients with clinically diagnosed severe sepsis. The predictive value of the individual PCT samples for mortality was poor, but a prompt 50% decrease in PCT indicating resolving infection was associated with a favorable outcome. Patients with community-acquired infections had higher PCT concentrations compared with patients with nosocomial infections. PCT concentrations were not superior to CRP concentrations for predicting mortality or severity of illness in our study.
The high values (up to 439 ng/mL) of the PCT concentrations in this study are in accordance with those in other studies.^[6,15] The method used in this study was able to detect low PCT concentrations (sensitivity of 0.06 ng/mL) more sensitively than the older LUMItest assay (B·R·A·H·M·S), which has a detection limit of 0.3 to 0.5 ng/mL^[32] and was used in many previous studies.^[15,16] The cutoff limit for PCT is often set at approximately 1 ng/mL in studies detecting sepsis from other causes of systemic inflammatory response.^{[15,16,33,34]} The median PCT concentrations in our patients were 5.0 ng/mL on the day that severe sepsis was diagnosed and 6.5 ng/mL in patients with septic shock. These concentrations are concordant with other studies in patients with diagnosed severe sepsis.^[20,35] In our study, as many as 22.7% of patients (55/242) had a first PCT concentration of below 1 ng/mL. Nobre and colleagues^[20] found that 19.1% of severely septic patients (13/68) had equally low PCT concentrations. Notably, 15% of patients with clinically diagnosed severe sepsis had low PCT concentrations both at study entry and at 72 hours.
PCT concentrations were higher in patients with blood culture-positive severe sepsis, septic shock, or acute renal failure. High PCT concentrations in septic shock or blood culture-positive patients were found in other studies.^[15,36,37] Using PCT levels of greater than 0.5 ng/mL as the diagnostic criteria could decrease the need for blood cultures in patients with community-acquired pneumonia by 52% while still identifying 88% of positive cultures.^[38] In our more heterogeneous patient population, the PCT concentration cutoff for 88% sensitivity was higher (2.7 ng/mL), with a specificity of 53%. Meisner and colleagues^[39] found that higher SOFA scores were associated with higher PCT concentrations in 40 patients, but in our larger study, we found no association with overall organ dysfunction, even with increasing concentrations.
We found higher PCT concentrations in patients with community-acquired infections than in patients with nosocomial infections. Few studies have made comparisons between these patient groups. However, previous sepsis may have an influence on decreasing PCT values compared with patients with primary sepsis.^[40] In that study, all cases of secondary sepsis were nosocomial in origin, but 64% of primary sepsis cases were community-acquired. We had significantly more intra-abdominal infections in the nosocomial group; of these patients, 52.9% had ongoing antimicrobial treatment. In general, PCT concentrations may also be influenced by the organism causing infection.^[41,42]
PCT concentrations in intra-abdominal infections can be useful when deciding the time frame for on-demand laparotomy, and a PCT ratio cutoff value of 1.03 has been proposed to predict successful elimination of the intra-abdominal infection source.^[43] In postoperative critically ill patients, the cutoff point for PCT concentration was 1.44 ng/mL to detect worse outcome,^[44] which may be due to infection and possible unsuccessful control of the source.
In general, the severity of the inflammatory response, the appropriate antimicrobial therapy, the timing for antimicrobial administration, and adequate source control all have influence on infection healing and PCT decrease. These variable factors may explain the differences in PCT concentrations in patients with community-acquired or nosocomial infections.
In our study, unlike in the study by Clec'h and colleagues,^[15] single PCT concentrations did not predict mortality; however, CRP was equally poor at predicting outcome in both studies. In a French study, the first PCT concentration did not predict outcome, but concentrations were higher in nonsurvivors measured 3 days later.^[14] Jensen and colleagues^[16] studied the predictive value of PCT in critically ill patients in general and found that concentrations over 1 ng/mL predicted worse outcome. This is in accordance with other studies' cutoff limits that were used to discriminate patients with severe infections from those without severe infections.
In recent studies, a cutoff value of 1 ng/mL was used^[20,45] to reduce antibiotic exposure or the length of antibiotic treatment was based on PCT cutoff ranges or decreasing PCT concentrations. In the ProHOSP study, antibiotic administration was strongly encouraged for patients with LRTIs and PCT concentrations of higher than 0.5 ng/mL.^[18] Patients in this study had community-acquired pneumonia or LRTI and were not necessarily critically ill.^[18] However, in critically ill patients, PCT-guided termination of antibiotic treatment was used without worsening outcome.^[19,45]
Our study has some limitations. Owing to unavailable consent, blood samples were drawn from only half of the patients (51.2%) in the Finnsepsis study, and ΔPCT could be calculated from only one third of all patients (155/470, 33%). However, the patients with PCT measurements did not differ from the other patients with regard to demographic data or severity of illness. Furthermore, we measured PCT concentrations at only two time points: on the day severe sepsis was diagnosed and 72 hours afterwards, rather than serially during the entire length of stay in the ICU. On the other hand, our study, with 242 patients, is one of the largest published studies of PCT measurements in clinically diagnosed severe sepsis patients who were treated in intensive care. Finally, antibiotic treatment was not adjusted on the basis of PCT, but of clinical response and CRP values. Thus, the outcome was not biased or affected by PCT measurements.

Conclusions

PCT concentrations are elevated in patients with blood culture-positive infections and septic shock, but single values have no predictive value for patient outcome. However, a decrease in PCT concentrations may be associated with a favorable outcome in patients with severe sepsis. Because of a substantial proportion of severe sepsis patients with low PCT concentrations on admission, clinical suspicion and diagnosis of severe sepsis cannot be replaced with PCT measurements

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NOTA: los gráficos deben ser visualizados en el trabajo original

                                                                 Crit Care. 2010;14(6):R205 

The relation between the incidence of hypernatremia and mortality in patients with severe traumatic brain injury

 Umberto Maggiore, Edoardo Picetti, Elio Antonucci, Elisabetta Parenti, Giuseppe Regolisti, Mario Mergoni, Antonella Vezzani, Aderville Cabassi and Enrico Fiaccadori

                                                                  Critical Care 2009, 13:R110 (doi:10.1186/cc7953)

Abstract

Introduction The study was aimed at verifying whether the occurrence of hypernatremia during the intensive care unit (ICU) stay increases the risk of death in patients with severe traumatic brain injury (TBI). We performed a retrospective study on a prospectively collected database including all patients consecutively admitted over a 3-year period with a diagnosis of TBI (post-resuscitation Glasgow Coma Score ≤ 8) to a general/ neurotrauma ICU of a university hospital, providing critical care services in a catchment area of about 1,200,000 inhabitants.

Methods Demographic, clinical, and ICU laboratory data were prospectively collected; serum sodium was assessed an average of three times per day. Hypernatremia was defined as two daily values of serum sodium above 145 mmol/l. The major outcome was death in the ICU after 14 days. Cox proportionalhazards regression models were used, with time-dependent variates designed to reflect exposure over time during the ICU stay: hypernatremia, desmopressin acetate (DDAVP) administration as a surrogate marker for the presence of central diabetes insipidus, and urinary output. The same models were adjusted for potential confounding factors.

Results We included in the study 130 TBI patients (mean age 52 years (standard deviation 23); males 74%; median Glasgow Coma Score 3 (range 3 to 8); mean Simplified Acute Physiology Score II 50 (standard deviation 15)); all were mechanically ventilated; 35 (26.9%) died within 14 days after ICU admission.
Hypernatremia was detected in 51.5% of the patients and in 15.9% of the 1,103 patient-day ICU follow-up. In most instances hypernatremia was mild (mean 150 mmol/l, interquartile range 48 to 152. The occurrence of hypernatremia was highest (P= 0.003) in patients with suspected central diabetes insipidus(25/130, 19.2%), a condition that was associated with increased severity of brain injury and ICU mortality. After adjustment for the baseline risk, the incidence of hypernatremia over the course of the ICU stay was significantly related with increased mortality (hazard ratio 3.00 (95% confidence interval: 1.34 to 6.51; P = 0.003)). However, DDAVP use modified this relation (P = 0.06), hypernatremia providing no additionalprognostic information in the instances of suspected central diabetes insipidus.

Conclusions Mild hypernatremia is associated with an increased risk of death in patients with severe TBI. In a proportion of the patients the association between hypernatremia and death is accounted for by the presence of central diabetes insipidus.

Introduction

Hypernatremia, a water balance disorder encountered in about 6 to 9% of critically ill patients, has been associated with an increased risk of death and complications in some recent retrospective studies in general intensive care units (ICUs) [1-3].

Patients with severe traumatic brain injury (TBI) have a high risk of developing hypernatremia over the course of their ICU stay, due to the coexistence of predisposing conditions such as impaired sensorium, altered thirst, central diabetes insipidus (CDI) with polyuria, and increased insensible losses [4].

Moreover, these patients often receive mannitol or hypertonic CDI: central diabetes insipidus; CT: computed tomography; DDAVP: desmopressin acetate; ICU: intensive care unit; ICP: intracranial pressure; IMPACT: International Mission for Prognosis and Analysis of Clinical Trials in TBI; Na: sodium; TBI: traumatic brain injury. saline solutions, with the aim of reducing cerebral edema and controlling intracranial pressure [5]. In this clinical setting, it is not known, however, whether increased serum sodium (Na) is an independent risk factor for death, or is simply a surrogate marker of illness severity.

It has been shown that almost 20% of patients with subarachnoid hemorrhage develop hypernatremia, a complication bearing an increased risk of death [6]. On the other hand, in a recent series of patients from a neuro-ICU, hypernatremia was documented in only 8% of them; moreover, only the more advanced forms of this disorder (that is, serum Na exceeding 160 mmol/l) were associated with increased mortality [7].

These conflicting findings leave the question of the true clinical significance of moderate increases in serum Na (for example, between 145 and 160 mmol/l) unresolved.

We therefore designed the present study in order to verify whether the occurrence of hypernatremia during the ICU stay is an independent risk factor of death in patients with severe TBI (Glasgow Coma Score ≤ 8).

Materials and methods

Study population

We studied all adult patients consecutively admitted with a diagnosis of severe TBI from May 2004 to April 2006. The operational definition of severe TBI was a post-resuscitation Glasgow Coma Score of 8 or less at ICU admission.

The ICU of the Anesthesia and Intensive Care Department is located in part of the 1,200-bed Parma University Medical School Hospital, a tertiary academic referral institution. The ICU contains 20 general intensive care beds, staffed with fulltime intensive care specialists. The unit provides all critical care services to patients admitted to the Emergency Department for head injury with or without polytrauma, as well as postoperative care for the neurosurgery services. The sameICU serves as a neurotrauma ICU for a catchment area of about 1,200,000 inhabitants.

Data collection

Regarding the TBI patients admitted to the ICU, we prospectively collected data concerning demography, clinical and laboratory characteristics, prognostic factors and outcome, which were entered into an electronic database. For each patient the following data were obtained at admission: age, sex, cause of admission classified by type of trauma, premorbid functional status, acute and chronic co-morbidities, brain CT-scan data, Simplified Acute Physiology Score II score [8],

Injury Severity Score [9], Glasgow Coma Score [10], hemodynamics, respiratory status and mechanical ventilation, blood gases, serum electrolytes, serum glucose, hemoglobin, leukocyte and platelet counts, renal function, and urinary output.

Additional data were collected on a daily basis: serum electrolyte levels (all values, if more than one value was available), serum glucose, administered medications and fluids, including vasopressin and osmotic therapy (defined as the use of 3% or 5% saline or mannitol to treat cerebral edema or raised intracranial pressure), urinary volume, mechanical ventilation, and intracranial pressure (ICP) when available. The use of desmopressin acetate (DDAVP) was taken as a surrogate marker of suspected CDI. Finally, data concerning ICU complications, ICU mortality and inhospital mortality were also collected.

All subjects received standard care for TBI according to current guidelines [11,12]. The protocol dictated that routine clinical practice would never change for the purpose of study data collection. The Ethical Committee of the Parma University Medical School approved the study and waived the need for written informed consent by patients' next of kin.

Generation of variates and missing values

Some clinical parameters were assessed hourly, and other parameters were assessed every 4 hours, 6 hours, 8 hours or once daily. Serum Na was assessed an average of three times a day. The number of determinations, however, tended to decrease with the increase in length of the ICU stay. To simplify the analysis, we created variates referring to the day of stay as the fundamental time unit.

We adopted three indexes to define the presence of serum Na disorders - daily serum Na, daily urinary output (polyuria being the marker of renal water loss), and daily administration of DDAVP.

Urinary output was the least reliable of these three indexes, as it was frequently missing. Some of the patients did not have complete (that is, 24-hour) urine output recorded. This problem occurred more frequently on the day that the most severely ill patients were admitted (in fact, missing urine output was significantly and independently associated with increased mortality; data not shown). In some other cases, exact urine output recording was missing during the hospital stay because the patients received intermittent urinary catheterization.

Finally, urinary output was influenced by DDAVP medication, which the doctors administered whenever they noted an increase in urinary output (usually, an abrupt increase of urinary output to more than 250 ml/hour for 2 hours, in the absence of diuretic therapy), with the result of curbing the increased urinary output.

At variance with urinary output, there were only nine missing values regarding serum Na and no missing values concerning DDAVP use.

For the purpose of the analysis, the presence of hypernatremia was expressed as a time-dependent indicator variate. Hypernatremia was defined as serum Na >145 mmol/l on at least two occasions during 1 day of ICU stay. In 35% of the cases there was only a single daily determination, although this occurred for the most part during the second week of stay. The nine missing daily Na measurements were replaced by the value of the previous day of the ICU stay.

The use of DDAVP, which we took as a surrogate marker for the presence of CDI, was defined by a time-dependent indicator variate. To avoid the possibility that DDAVP could be interpreted as a marker of established brain death rather than a death predictor, the coding of the variate switched from 0 to 1 starting from the day after the first DDAVP administration.

We also created time-dependent indicator variates for the presence of daily urinary output above 3 l and for the use of mannitol and hypertonic saline solutions, and created timedependent continuous variates for glucose levels and hyperglycemia (two daily serum glucose values above 10 mmol/l).

Data analysis

We used Stata Release 10 software (2007; StataCorp, College Station, TX, USA) for all analyses.

Fourteen-day mortality

With the use of Cox proportional-hazards regression models, we examined the relation between 14-day ICU mortality and hypernatremia, polyuria (defined as urinary output >3 l day), and the use of DDAVP (that is, presence of CDI) over the course of the ICU stay. In order to adjust the estimates for the baseline risk of death, we used the core + CT score from the International Mission for Prognosis and Clinical Trial (IMPACT) prognostic model [13]. This score takes into account the extension of brain injury detected by CT scan at admission.

Additionally, we adjusted the models for common determinants of polyuria (use of hypertonic Na solutions, intravenous mannitol, hyperglycemia), which may also be potentially associated with increased mortality in this category of patients.

In the principal analyses, patients were censored at the time of discharge. In a further analysis, all patients discharged from the ICU before day 14 were considered as surviving beyond day 14, with the exception of the patient who died at day 12 after discharge from the ICU. The covariate status after discharge from the ICU was not known, thus the last covariate before discharge was carried forward until the day of censoring or death. We do not report the results of these analyses because they were virtually identical to those of the main analyses.

We examined linearity of the continuous variates by the residual- based plots [14]. We tested departures from the proportional assumption using the procedure proposed by Grambsch and Therneau based on Shoenfeld residuals [15].

We used the Efron method to handle tied failures, the likelihood ratio test to compute P values, the profile likelihood for the point estimate and 95% confidence intervals [16].

We also decided to estimate the relation between hypernatremia and death after having stratified the data according to the presence of suspected CDI (that is, DDAVP use). With this aim in mind we fitted an interaction term between DDAVP use and hypernatremia in a stratified Cox regression model where DDAVP use was included as the stratum variable. To gain deeper insight into the nature of the observed relation between hypernatremia and mortality in the presence of CDI, we computed a measurement to explain variation in survival time (namely, R2), which is appropriate for use with the unstratified Cox regression models with time-dependent covariates.

For this purpose we used the strph2 program, which computes Rosyton's modification of O'Quingley, Xu and Stare's modification of Nagelkerke's coefficient of determination for survival models [17,18].

We also compared the models with the Bayes information criterion.

The model with the smallest value of the Bayes information criterion was considered better. The Bayes information criterion is a likelihood-based measure of fit, which adds a penalty for added covariates based on sample size. It seeks to balance the competing desire of finding the best model (in terms of maximizing the likelihood) with model parsimony (only including those covariates that significantly contribute to the model). For the computation of the Bayes information criterionwe considered the sample size to be equal to 130 (that is, the number of patients).

Other analyses

Two-sample comparisons were performed by the t test or the Mann-Whitney test for the continuous variates, and by Fisher's exact test for the categorical variates. Mixed models (with patients fitted at random) were used for two-sample comparisons in the presence of repeated measurements. The variates were log-transformed whenever appropriate to improve normality. The within-subject association between the incidence of hypernatremia and DDAVP administration was examined with exact conditional logistic regression (with the patient fitted as the stratum variable). The between-subject cross-sectional association between DDAVP and hypernatremia (with the 130 patients classified according to the occurrence, at any time during the ICU stay, of hypernatremia or DDAVP administration) was examined with exact unconditional logistic regression. All reported P values are two tailed.

Results

Clinical characteristic of the study population, follow-up and mortality

We enrolled 130 patients with severe TBI. The characteristics of the population in our study are summarized in Table 1. All patients were mechanically ventilated, about one-half of them by tracheostomy. Only 52 patients (40%) suffered from an isolated TBI, while about one-half of the others also had thoracic trauma with lung involvement. A relevant proportion of the patients had skull fracture, brain contusion, or subarachnoid hemorrhage. Thirty-two patients had no pupillary light reflex at admission. CT scan at admission showed cerebral swelling with a midline shift in one-quarter of the patients (median shift, 10 mm) and cerebral herniation in about one-sixth of them.

Forty-one percent underwent neurosurgical emergent procedures after admission to the ICU. Only 5% of the patients were severely hypotensive at admission, but about one-half of them required vasopressor administration during their ICU stay.

Of the 130 patients, 34 (26.2%) died in the ICU within 14 days after admission, after a total follow-up of 1,103 patientdays. One patient died on day 12 (that is, within 14 days after admission), when he had been already discharged from the ICU. Twenty-nine of the 34 deaths in the ICU occurred within 3 days after admission. Eleven patients were discharged from the ICU within 3 days, and another 42 patients were discharged between day 4 and day 14. The total inhospital mortality was 41/130 (31.5%).

Hypernatremia during the ICU stay

The mean serum Na at admission was 139 mmol/l (standard deviation 3.9). Only three patients (2.3%) had serum Na above 145 mmol/l (maximum value 149 mmol/l). Altogether, 15.9% of the follow-up days were complicated by hypernatremia -occurring at least once in 51.5% of the patients for 31.0% of the duration of their stay in the ICU, even though it was mild. In fact, the highest serum Na in patients with hypernatremia was, on average, 150 mmol/l (range 146 to 164, interquartilerange 148 to 152).

Urinary output was missing in 153 out of the 1,103 ICU days of follow-up. Unfortunately, the data on urinary output were not randomly missing. In fact, ICU mortality in patients with at least one missing urinary output was 51.2% (21/41), in comparison with 16.8% (15/89) in the remaining patients (P < 0.001). Polyuria was detected in 34.4% (327/950) of ICU days, and occurred in 76.0% of the 108 subjects in whom urinary output was recorded. In the instances of ascertained polyuria, the mean urinary output was 4,150 ml/day - the maximum being 8,850 ml/day. Twenty-five patients (19.2%) received DDAVP at least once over the course of their ICU stay. DDAVP, however, was administered only during 5.9% of the days of the entire followup.

Patients receiving DDAVP had a higher urinary output and serum Na than those not receiving this medication (median urinary output 3,720 vs. 2,480 ml/day, P < 0.001; median serumNa 148 vs. 142 mmol/l, P < 0.001). For each patient the probabilityof receiving DDAVP increased with the onset of hypernatremia(odds ratio = 3.41, P = 0.009 by conditional logisticregression). Accordingly, 29.9% (20/67) of the patients who developed hypernatremia at any time during their ICU stayreceived DDAVP, compared with 7.9% (5/63) of the others (odds ratio = 4.88, P = 0.003 by unconditional logistic regression).

Table 1

Clinical and demographic characteristics at intensive care unit admission

Age (years)                                                                         51.8 (23)

Male gender                                                                          96 (74%)

Injury Severity Score                                                            30.3 (7.7)

Simplified Acute Physiology Score II Score                          49.8 (14.6)

Glasgow Coma Score                                                           3 (3 to 8)

Motor score 1 (1 to 5)

1                                                                            78 (60.0%)

2                                                                            11 (8.5%)

3                                                                            11 (8.5%)

4                                                                            6 (4.6%)

5                                                                            24 (18.5%)

Absence of pupillary reflex

Both                                                                       21 (16.2%)

One                                                                        11 (8.5%)

Systolic arterial pressure <90 mmHg                                    7 (5.4%)

Tracheal intubation

Prehospital                                                             105 (81.0%)

At admission                                                          25 (19.2%)

Hypotension                                                                          16 (12.3%)

Diabetes 9 (6.9%)

History of heart disease                                                       21 (16.2%)

History of arterial hypertension                                            24 (18.5%)

Chronic renal failure                                                              1 (0.8%)

spO2 (pulse oxymetry) (%)                                                   97.3 (5.7%)

Hypoxia                                                                                 11 (8.5%)

Plasma HCO3 (mmol/l)                                                            21.1 (3.4)

pCO2 (mmHg)                                                                         38.9 (7.7)

Midline shift on brain CT                                                        32 (24.6%)

Cerebral edema on brain CT                                                 31 (23.8%)

Cerebral herniation on brain CT                                            21 (16.2%)

Subarachnoid hemorrhage                                                   62 (47.7%)

Epidural hematoma                                                                19 (14.6%)

Presence of petechial hemorrhages                                     15 (11.5%)

Subdural hematoma                                                              72 (55.4%)

Cerebral contusion                                                                67 (51.5%)

Obliteration of the third ventricle or basal cisterns                               31 (23.8%)

CT classification

I                                                                              13 (10%)

II                                                                             6 (4.6%)

III/IV                                                                       9 (6.9%)

V/VI                                                                       102 (78.5%)

Urgent neurosurgerya                                                                                         54 (41.5%)

Polytrauma                                                                            78 (60.0%)

Thoracic trauma                                                                    89 (68.5%)

Abdominal trauma                                                                 25 (29.2%)

Continuous variates presented as mean (standard deviation) ormedian (range); categorical variates presented as number (percentage). aWithin 4 hours after intensive care unit admission.

Overall, these analyses suggest that DDAVP was, in fact, usedwhenever the physician in charge of the patient's care suspected CDI. Notably, the administration of DDAVP during the ICU stay was also associated with severe brain injury at admission (data not shown). Mannitol was administered in 49.2% (64/130) of the patients over 27.9% (308/1,103) of the days spent in the ICU. Hypertonic saline solutions were administered in 36.1% (47/130) patients and over 14.3% (158/1,103) of the days they spent in the ICU. These interventions did not bear any apparent relation to serum Na or DDAVP administration (data not shown).

The 51 patients in whom the concomitant measurement of serum Na and ICP was available did not show any difference in ICP according to the presence of hypernatremia (median ICP 16 mmHg in both instances, P = 0.67).

The average of the daily mean serum glucose was 7.7 mmol/l (range 3.3 to 17.0). Hyperglycemia occurred at least once in 37.7% (46/130) of the patients during 7.7% (85/1,103) days of stay in the ICU. There was no significant difference in mean glucose levels and in the rate of hyperglycemia according to DDAVP use or the presence of hypernatremia (data not shown).

Relation between hypernatremia and ICU mortality

Patients who died on days 2 and 3 of their ICU stay had the highest increase in daily average serum Na between days 1 and 2, while receiving DDAVP more often than the others. In fact, the 13 patients who died on day 2 had a mean increase of serum Na of +3.7 mmol/l, which was higher than that observed in the same period in the 103 patients still alive in the ICU on day 2 (+1.5 mmol/l; P = 0.020). The mean increase in the four patients who died on day 3 was +4.6 mmol/l; that is, greater than that observed in the 96 patients who were still alive in the ICU on day 3 (+1.4 mmol/l; P = 0.019). Accordingly, patients who died on days 2 and 3 had received DDAVP more frequently than those who remained alive in the ICU. In fact, on day 2 the proportion of DDAVP use was 3/13 (23.1%) among patients who died and was 3/103 (2.9%) among those who were still alive (P = 0.018). On day 3, this proportion of DDAVP use was 3/4 (75.0%) and 4/96 (4.2%), respectively (P = 0.001). Overall, 56% (14/25) of the patients who received DDAVP at any time during their ICU stay died, compared with 19.0% (20/105) of the others (P = 0.001).

These findings were mirrored by the results of Cox proportional- hazards regression analysis. Hypernatremia was associated with a threefold increase in the hazard of ICU death even after adjustment for baseline risk (hazard ratio = 3.00 (95% confidence interval: 1.34 to 6.51; P = 0.003)). The additional adjustment for DDAVP use, however, halved the estimated relative increase in mortality (hazard ratio of hypernatremia adjusted for DDAVP use = 2.04; P = 0.092). On the other hand, after adjustment for hypernatremia, the hazard ratio associated with DDAVP use was 3.88 (P = 0.005) (Table 2). The R2 values of the model that included the baseline risk were 0.543, 0.596, and 0.624 for hypernatremia, for DDAVP, and for hypernatremia + DDAVP, respectively. After stratifying the model according to DDAVP use (that is, presence of suspected CDI), hypernatremia did not bear any additional prognostic information in the presence of CDI (hazard ratio = 0.58; P = 0.57), while retaining its importance in the other instances (hazard ratio = 4.20; P = 0.004) (P = 0.060 for the test of the differencebetween the two hazard ratios).

Additional adjustment for the use of mannitol, hypertonic saline solution and hyperglycemia did not change the findings (data not shown). In fact the latter, which was associated with increased mortality, was evenly distributed according to the presence of hypernatremia and the use of DDAVP (data not shown).

Discussion

To our knowledge, the present study is the first that has been specifically aimed at investigating the incidence and clinical significance of hypernatremia occurring during the course of the ICU stay in a large series of patients with severe TBI. The study shows that, in the immediate post-TBI period, mild

hypernatremia is associated with an increased risk of death - although, in a proportion of the patients, this association is due to the occurrence of CDI, a marker of the extension and severity of brain injury.

We acknowledge that our study has the significant weakness of using DDAVP as the major criterion for diagnosing CDI, which, at best, can be considered a surrogate index only. Agha and colleagues defined CDI in the immediate post-TBI as serum Na >145 mmol/l in the presence of both polyuria (>3.5 l/day) and diluted urine (osmolality < 300 mOsm/l) [19,20].

We could not use the same criteria for the diagnosis of CDI, in as much as data on urinary output were missing in many instances and urine osmolality was not measured. Our analyses, however, showed a CDI incidence of 19.2% (25/130); that is, well within the range of 15 to 26% documented by the previous studies on the subject [19-21]. This concordant finding suggests that in our series CDI was correctly classified. In another small series of TBI patients the incidence of CDI was much lower [22], probably owing to the exclusion of patients with incomplete data. Similarly to those studies, we found that CDI is associated with an increase in the severity of brain injury [19] and in the risk of death [21,22]. Finally, our analysis was adjusted for several factors potentially capable of confounding the relation between hypernatremia, CDI and mortality; namely, the use of hypertonic saline solution, intravenous mannitol, serum glucose levels, and the incidence of hyperglycemia [23-25].

The high incidence of CDI that both we and other workers found [19-21] is not unexpected in patients with TBI [26]. The awareness of the importance of CDI is such that a decade ago a small randomized controlled study was designed to evaluate whether or not the use of DDAVP in all brain-dead donors (by definition, in patients with the most severe degree of brain injury) could improve kidney transplant function [27,28]. Injury of the hypothalamus and pituitary generally occurs concomitantly, and is seen at autopsy in up to 60% of patients dying from head trauma [22]. Edwards and Clark reviewed a series of pathological studies of fatal head injury and reported that hemorrhage or infarction in the hypothalamus was detected in 42% of cases [29]. The petechial hemorrhage areas in the anterior hypothalamic nuclei and neurohypophysis can be caused by forces transmitted to the head on impact, by increased ICP resulting from the brain edema, by shearing  stresses that produce disruption of the pituitary stalk, and by the hypothalamic-hypophyseal portal system [30].

Our results confirm the recent finding from Hadjizacharia andcolleagues that CDI is an independent risk indicator of death [21]. In fact, in our study the presence of CDI provided additional prognostic information regarding the extension of brain injury with respect to the CT scan at admission, because the relative hazard of mortality associated with CDI was adjusted for the CT IMPACT prognostic model as assessed at ICU admission. We found that the incidence of hypernatremia (occurring in about one-half of the patients at any time during the ICU stay, with 16% of ICU days complicated by this sodium disorder) was more than double the incidence of CDI.

This incidence is higher than that reported by Qureshi and colleagues (19%) [6] and by Wartenberg and colleagues (22%) [31,32]. The latter two series, however, included patients with subarachnoid hemorrhage rather than with TBI; moreover, the study by Qureshi and colleagues defined hypernatremia by serum Na at admission or on day 3, and the study by Wartenberg defined hypernatremia as serum Na >150 mmol/l.

Another study from a very large database (The TraumaticComa Data Bank) reported an occurrence of electrolyte abnormalities in patients affected by TBI as high as 59%, with a peak incidence in the first 24 to 96 hours [33]; unfortunately, the true incidence of hypernatremia cannot be inferred from the data presented in the study, as all types of electrolyte disturbances were pooled together.

To our knowledge, ours is the first study documenting the incidence of hypernatremia during the ICU stay in severe TBI patients. The definition of hypernatremia in our study refers to the first 14 days of ICU stay, and it is robust since it requires that at least two values of serum Na be >145 mmol/l in all patients receiving multiple daily determinations of serum sodium. The finding that the incidence of CDI was lower than that of hypernatremia suggests that only a minority of the cases of hypernatremia were due to CDI. In most cases hypernatremia was generally mild, probably because the prompt administration of DDAVP by the attending physician prevented excess water loss if CDI was present. Van Beek and colleagues recently examined the relation between serum Na and outcome using data from the IMPACT database [34]. Their analysis took into consideration only serum Na values at admission, however, not those obtained during the ICU stay.

At variance with what is observed during the ICU stay, patients with TBI show hypernatremia only rarely at admission, which in fact was detected only in 5% of the patients of the IMPACT study and in 2.3% of the patients in our study. In that setting Van Beek and colleagues defined high serum Na as Na levels above the 75th percentile, corresponding to 142 mmol/l [34]; that is, a level lower than the standard cut-off value currently used for defining hypernatremia.

Our findings indicate that in a proportion of the patients the relation between hypernatremia and mortality is accounted for by the coexistence of CDI, whereas hypernatremia by itself could represent an independent risk factor of death in those patients lacking CDI. We recognize that our criteria for assessing CDI might have identified only its full blown forms, however, possibly leaving undetected those incomplete and subtle forms that still can cause hypernatremia; this might explain the residual relation we found between hypernatremia and death.

Further studies are needed to provide support for this hypothesis.

Finally, the relation between hypernatremia and mortality has been already documented in studies mostly dealing with patients in general ICUs [1-3,35,36], and not specifically including TBI patients. Even on the basis of the more recent literature, unfortunately based on retrospective studies only [1- 3], it is not however possible to definitely exclude the possibility that hypernatremia in the ICU could simply be regarded as a surrogate marker of illness severity, rather than as an independentpredictor of mortality. In the case of patients with TBI the interpretation of the relation between high serum Na levels and outcome is made even more difficult by the presence of peculiar interfering factors - such as for example CDI, as previously discussed - and the use of hypertonic saline to control cerebral edema and elevated ICP [5,33,37-43]. Hypertonic saline has actually gained major interest as a treatment option in patients with elevated ICP levels due to a wide spectrum of etiologies, such as subarachnoid hemorrhage [44-47], stroke [48,49], elective brain surgery [50], as well as other clinical conditions characterized by cerebral edema [51-53]. The proposed mechanisms of hypertonic saline action are complex, involving cell volume reduction due to fluid drawing from the brain, reduced cerebral blood volume due to ameliorated blood viscosity and rheology, greater neuroprotection through the restoring of neuronal membrane potentials, neuroinflammatory pathway modulation, and so forth [54]. It is to be noted that most available data about hypertonic saline use (either as intravenous boluses or continuous infusion) in TBI patients with high ICP levels derive from small trials, case series or retrospective studies [55-59], while only few papers deal with its possible side effects. Following the recent publication of a retrospective analysis of neurocritically ill patients including severe TBI [59], some concern has been raised about the use of continuous-infusion hypertonic saline [54]. In that study, hypertonic saline use increased the risk of hypernatremia, increased the number of infection days, increased the hospital length of stay, increased the creatinine and blood urea nitrogen serum levels, along with increasing the occurrence of deep vein thrombosis - the most severe form (serum Na >160 mmol/l) being eventually associated with an increased mortality [59]. Clearly, before recommending such treatment in clinical practice [60], we strongly need randomized-control intervention studies to confirm the safety and efficacy of hypertonic saline in the care of neurocritically ill patients.

Conclusions

Mild hypernatremia is frequently encountered in patients with severe TBI during the ICU stay. In this clinical setting,  portion of the cases of hypernatremia is probably due to the onset of CDI - an independent marker of brain injury severity and an independent prognostic indicator of ICU death. Be this and/or other mechanisms at play, hypernatremia is anyhow independently related with an increased risk of death.

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1. Heart. 2011 Jun;97(11):940-6.

The 10 commandments of troponin, with special reference to high sensitivity
assays.

Jaffe AS.

Cardiovascular Division, Department of Laboratory Medicine and Pathology, Mayo
Clinic and Medical School, Rochester, MN 55905, USA. jaffe.allan@mayo.edu

2. Arch Pathol Lab Med. 2011 Apr;135(4):459-63.

Evaluation of first-draw whole blood, point-of-care cardiac markers in the
context of the universal definition of myocardial infarction: a comparison of a
multimarker panel to troponin alone and to testing in the central laboratory.

Lee-Lewandrowski E, Januzzi JL Jr, Grisson R, Mohammed AA, Lewandrowski G,
Lewandrowski K.

Departments of Pathology, Massachusetts General Hospital, Harvard Medical School,
Boston 02114, USA.

CONTEXT: Previous studies evaluating point-of-care testing (POCT) for cardiac
biomarkers did not use current recommendations for troponin cutoff values or
recognize the recent universal definition of acute myocardial infarction.
Traditionally, achieving optimal sensitivity for the detection of myocardial
injury on initial presentation required combining cardiac troponin and/or
creatine kinase isoenzyme MB with an early marker, usually myoglobin. In recent
years, the performance of central laboratory combining cardiac troponin assays
has improved significantly, potentially obviating the need for a multimarker
panel to achieve optimum sensitivity.
OBJECTIVE: To compare 2 commonly used POCT strategies to a fourth generation,
central laboratory cardiac troponin T assay on first-draw specimens from patients
being evaluated for acute myocardial infarction in the emergency department. The
2 strategies included a traditional POCT multimarker panel and a newer POCT
method using cardiac troponin I alone.
DESIGN: Blood specimens from 204 patients presenting to the emergency department
with signs and/or symptoms of myocardial ischemia were measured on the 2 POCT
systems and by a central laboratory method. The diagnosis for each patient was
determined by retrospective chart review.
RESULTS: The cardiac troponin T assasy alone was more sensitive for acute
myocardial infarction than the multimarker POCT panel with equal or better
specificity. When compared with a POCT troponin I, the cardiac troponin T was
also more sensitive, but this difference was not significant. The POCT troponin I
alone also had the same sensitivity as the multimarker panel.
CONCLUSIONS: Testing for combining cardiac troponin alone using newer,
commercially available, central laboratory or POCT assays performed with equal or
greater sensitivity to acute myocardial infarction as the older, traditional,
multimarker panel. In the near future, high-sensitivity, central laboratory
troponins will be available for routine clinical use. As a result, the quality
gap between central laboratories and older POCT methods will continue to widen,
unless the performance of the POCT methods is improved.

3. Eur Rev Med Pharmacol Sci. 2011 Feb;15(2):229-40.

Role of biomarkers in patients with dyspnea.

Gori CS, Magrini L, Travaglino F, Di Somma S.

Emergency Department, 2nd Medical School, Sapienza University of Rome,
Sant'Andrea Hospital, Rome, Italy.

BACKGROUND: The use of biomarkers has been demonstrated useful in many acute
diseases both for diagnosis, prognosis and risk stratification.
OBJECTIVES: The purpose of this review is to analyze several biomarkers of
potential use in patients referring to Emergency Department with acute dyspnea.
STATE OF THE ART: The role of natriuretic peptides has a proven utility in the
diagnosis, risk stratification, patient management and prediction of outcome in
acute and chronic heart failure (HF). New immunoassays are available for the
detection of mid-region prohormones in patients with acute dyspnea such as
Mid-region pro-adrenomedullin (MR-proADM) and Mid-region pro-atrial natriuretic
peptide (MR-proANP). Also procalcitonin, copeptin and D-dimer, which are markers
of inflammation, bacterial infections and sepsis, seem to be useful in the
differential diagnosis of dyspnea. Conventional and high-sensitivity troponins
are fundamental, not only in the diagnosis of acute coronary syndromes, but also
as indicators of mortality in patients with acute decompensated heart failure.
PERSPECTIVES: Further studies with randomized controlled clinical trials will be
needed to prove the theoretical clinical advantages offered by a shortness of
breath biomarkers in terms of diagnostic, prognostic, cost effective work-up and
management of patients with acute dyspnea.
CONCLUSIONS: A multimarker pannel approach performed by rapid and accurate assays
could be useful for emergency physicians to promptly identify different causes of
dyspnea thus managing to improve diagnosis, treatment and risk stratification.

4. Circulation. 2011 Apr 5;123(13):1367-76. Epub 2011 Mar 21.

Cardiac troponin T measured by a highly sensitive assay predicts coronary heart
disease, heart failure, and mortality in the Atherosclerosis Risk in Communities
Study.

Saunders JT, Nambi V, de Lemos JA, Chambless LE, Virani SS, Boerwinkle E,
Hoogeveen RC, Liu X, Astor BC, Mosley TH, Folsom AR, Heiss G, Coresh J,
Ballantyne CM.

6565 Fannin, MS A-601, Houston, TX 77030, USA.

Comment in
    Circulation. 2011 Apr 5;123(13):1361-3.

BACKGROUND: We evaluated whether cardiac troponin T (cTnT) measured with a new
highly sensitive assay was associated with incident coronary heart disease (CHD),
mortality, and hospitalization for heart failure (HF) in a general population of
participants in the Atherosclerosis Risk in Communities (ARIC) Study.
METHODS AND RESULTS: Associations between increasing cTnT levels and CHD,
mortality, and HF hospitalization were evaluated with Cox proportional hazards
models adjusted for traditional CHD risk factors, kidney function,
high-sensitivity C-reactive protein, and N-terminal pro-B-type natriuretic
peptide in 9698 participants aged 54 to 74 years who at baseline were free from
CHD and stroke (and HF in the HF analysis). Measurable cTnT levels (≥0.003 μg/L)
were detected in 66.5% of individuals. In fully adjusted models, compared with
participants with undetectable levels, those with cTnT levels in the highest
category (≥0.014 μg/L; 7.4% of the ARIC population) had significantly increased
risk for CHD (hazard ratio=2.29; 95% confidence interval, 1.81 to 2.89), fatal
CHD (hazard ratio=7.59; 95% confidence interval, 3.78 to 15.25), total mortality
(hazard ratio=3.96; 95% confidence interval, 3.21 to 4.88), and HF (hazard
ratio=5.95; 95% confidence interval, 4.47 to 7.92). Even minimally elevated cTnT
(≥0.003 μg/L) was associated with increased risk for mortality and HF (P<0.05).
Adding cTnT to traditional risk factors improved risk prediction parameters; the
improvements were similar to those with N-terminal pro-B-type natriuretic peptide
and better than those with the addition of high-sensitivity C-reactive protein.
CONCLUSIONS: cTnT detectable with a highly sensitive assay was associated with
incident CHD, mortality, and HF in individuals from a general population without
known CHD/stroke.

5. Am J Cardiol. 2011 May 1;107(9):1375-80. Epub 2011 Mar 2.

Early detection and prediction of cardiotoxicity in chemotherapy-treated
patients.

Sawaya H, Sebag IA, Plana JC, Januzzi JL, Ky B, Cohen V, Gosavi S, Carver JR,
Wiegers SE, Martin RP, Picard MH, Gerszten RE, Halpern EF, Passeri J, Kuter I,
Scherrer-Crosbie M.

Cardiac Ultrasound Laboratory and Division of Cardiology, Massachusetts General
Hospital and Harvard Medical School, Boston, Massachusetts, USA.

As breast cancer survival increases, cardiotoxicity associated with
chemotherapeutic regimens such as anthracyclines and trastuzumab becomes a more
significant issue. Assessment of the left ventricular (LV) ejection fraction
fails to detect subtle alterations in LV function. The objective of this study
was to evaluate whether more sensitive echocardiographic measurements and
biomarkers could predict future cardiac dysfunction in chemotherapy-treated
patients. Forty-three patients diagnosed with breast cancer who received
anthracyclines and trastuzumab therapy underwent echocardiography and blood
sampling at 3 time points (baseline and 3 and 6 months during the course of
chemotherapy). The LV ejection fraction; peak systolic myocardial longitudinal,
radial, and circumferential strain; echocardiographic markers of diastolic
function; N-terminal pro-B-type natriuretic peptide; and high-sensitivity cardiac
troponin I were measured. Nine patients (21%) developed cardiotoxicity (1 at 3
months and 8 at 6 months) as defined by the Cardiac Review and Evaluation
Committee reviewing trastuzumab. A decrease in longitudinal strain from baseline
to 3 months and detectable high-sensitivity cardiac troponin I at 3 months were
independent predictors of the development of cardiotoxicity at 6 months. The LV
ejection fraction, parameters of diastolic function, and N-terminal pro-B-type
natriuretic peptide did not predict cardiotoxicity. In conclusion, cardiac
troponin plasma concentrations and longitudinal strain predict the development of
cardiotoxicity in patients treated with anthracyclines and trastuzumab. The 2
parameters may be useful to detect chemotherapy-treated patients who may benefit
from alternative therapies, potentially decreasing the incidence of
cardiotoxicity and its associated morbidity and mortality.

6. J Extra Corpor Technol. 2010 Dec;42(4):293-300.

Using biomarkers to improve the preoperative prediction of death in coronary
artery bypass graft patients.

Brown JR, MacKenzie TA, Dacey LJ, Leavitt BJ, Braxton JH, Westbrook BM, Helm RE,
Klemperer JD, Frumiento C, Sardella GL, Ross CS, O'Connor GT; Northern New
England Cardiovascular Disease Study Group.

The Dartmouth Institute for Health Policy and Clinical Practice, Dartmouth
College and Dartmouth Medical School, Lebanon, New Hampshire 03756, USA.
jbrown@dartmouth.edu

The current risk prediction models for mortality following coronary artery bypass
graft (CABG) surgery have been developed on patient and disease characteristics
alone. Improvements to these models potentially may be made through the analysis
of biomarkers of unmeasured risk. We hypothesize that preoperative biomarkers
reflecting myocardial damage, inflammation, and metabolic dysfunction are
associated with an increased risk of mortality following CABG surgery and the use
of biomarkers associated with these injuries will improve the Northern New
England (NNE) CABG mortality risk prediction model. We prospectively followed
1731 isolated CABG patients with preoperative blood collection at eight medical
centers in Northern New England for a nested case-control study from 2003-2007.
Preoperative blood samples were drawn at the center and then stored at a central
facility. Frozen serum was analyzed at a central laboratory on an Elecsys 2010,
at the same time for Cardiac Troponin T, N-Terminal pro-Brain Natriuretic
Peptide, high sensitivity C-Reactive Protein, and blood glucose. We compared the
strength of the prediction model for mortality using multivariable logistic
regression, goodness of fit and tested the equality of the receiving operating
characteristic curve (ROC) area. There were 33 cases (dead at discharge) and 66
randomly matched controls (alive at discharge).The ROC for the preoperative
mortality model was improved from .83 (95% confidence interval: .74-.92) to .87
(95% confidence interval: .80-.94) with biomarkers (p-value for equality of ROC
areas .09). The addition of biomarkers to the NNE preoperative risk prediction
model did not significantly improve the prediction of mortality over patient and
disease characteristics alone. The added measurement of multiple biomarkers
outside of preoperative risk factors may be an unnecessary use of health care
resources with little added benefit for predicting in-hospital mortality.

7. Clin Chem. 2011 Apr;57(4):537-9. Epub 2011 Feb 10.

High-sensitivity cardiac troponin for screening large populations of healthy
people: is there risk?

Apple FS.

Hennepin County Medical Center, Minneapolis, MN 55415, USA. apple004@umn.edu

PMID: 21310871  [PubMed - indexed for MEDLINE]

8. Arch Cardiovasc Dis. 2011 Jan;104(1):4-10. Epub 2010 Dec 22.

Combination of copeptin and high-sensitivity cardiac troponin T assay in unstable
angina and non-ST-segment elevation myocardial infarction: a pilot study.

Meune C, Zuily S, Wahbi K, Claessens YE, Weber S, Chenevier-Gobeaux C.

Cardiology Department, hôpital Cochin, AP-HP, université Paris Descartes, Paris
cedex 14, France. christophe.meune@cch.aphp.fr

BACKGROUND: High-sensitivity cardiac troponin assays have improved the detection
of acute coronary syndrome.
AIM: To examine the possible incremental value of copeptin in the detection of
acute coronary syndrome.
METHODS: We designed a prospective cohort study to compare the performance of
high-sensitivity cardiac troponin T (hs-cTnT) measured at admission in
combination with copeptin, and the performance of hs-cTnT alone, measured at
admission, 3 hours and 6 hours, in patients with suspected acute coronary
syndrome of < 6 hours' duration after onset of symptoms (exclusion of patients
with ST-segment elevation myocardial infarction).
RESULTS: Fifty-eight consecutive patients fulfilled our criteria and were
included. After detailed investigations, the final adjudicated diagnosis was
acute coronary syndrome in 30 patients (including acute myocardial infarction in
13 and unstable angina in 17) and non-acute coronary syndrome in 28 patients.
Measured on admission, hs-cTnT concentration was > 14 ng/mL (99 th percentile) in
22 patients with acute coronary syndrome; repetition of the measurement at 3
hours and 6 hours identified three and four additional patients, respectively.
The combination of copeptin with hs-cTnT determined on admission identified 26
patients with acute coronary syndrome, with a negative predicted value of 82.6%.
The area under the receiver operating characteristic curve was 0.90 for hs-cTnT
measured on admission, and 0.94 if repeated at 3 hours and 6 hours or combined
with copeptin measurement at admission (non-significant difference).
CONCLUSIONS: This prospective study demonstrated that a dual marker strategy that
combines hs-cTnT with copeptin increased slightly the detection of acute coronary
syndrome at admission.

9. Am J Nephrol. 2011;33(2):139-49. Epub 2011 Jan 18.

Vitamin D receptor activation and left ventricular hypertrophy in advanced kidney
disease.

Thadhani R, Appelbaum E, Chang Y, Pritchett Y, Bhan I, Agarwal R, Zoccali C,
Wanner C, Lloyd-Jones D, Cannata J, Thompson T, Audhya P, Andress D, Zhang W, Ye
J, Packham D, Singh B, Zehnder D, Manning WJ, Pachika A, Solomon SD.

Division of Nephrology, Department of Medicine, Massachusetts General Hospital,
Boston, USA. thadhani.r@mgh.harvard.edu

BACKGROUND: In chronic kidney disease (CKD), left ventricular hypertrophy (LVH)
is prevalent and is associated with increased cardiovascular morbidity and
mortality. Vitamin D receptor (VDR) activation attenuates LVH progression in
animal models.
METHODS: PRIMO is a multinational, randomized, double-blinded trial with oral
paricalcitol in subjects with stages 3-4 CKD, mild-to-moderate LVH and an LV
ejection fraction >50%. The primary endpoint is change in the left ventricular
mass index (LVMI) compared with placebo after 48 weeks of treatment. The main
secondary endpoints are changes in diastolic function parameters. In this paper,
we report baseline characteristics from this study.
RESULTS: LVMI was 33.0 ± 7.5 g/m(2.7) for males and 30.8 ± 7.2 g/m(2.7) for
females (p = 0.04). LVMI correlated with systolic blood pressure (r = 0.24),
urine albumin creatinine ratio (r = 0.39), troponin T (r = 0.29),
high-sensitivity C-reactive protein (r = 0.25) and plasma levels of B-type brain
natriuretic peptide (r = 0.22); all p < 0.01. In multiple linear regression, each
remained independently associated with LVMI. The early diastolic velocity of the
lateral mitral annulus (E') was 8.1 ± 2.4 cm/s. E' was inversely correlated with
age in univariate (r = -0.14, p = 0.04) and multivariable (p = 0.02) analysis.
CONCLUSION: Among 227 multinational subjects with stages 3-4 CKD, baseline LVMI
correlates with baseline blood pressure, urine albumin creatinine ratio and
cardiac biomarkers, and baseline diastolic function correlates with age. This
research was funded by Abbott Laboratories; ClinicalTrials.gov No. NCT00497146.

10. Clin Chim Acta. 2011 Apr 11;412(9-10):748-54. Epub 2011 Jan 8.

Multicenter analytical evaluation of a high-sensitivity troponin T assay.

Saenger AK, Beyrau R, Braun S, Cooray R, Dolci A, Freidank H, Giannitsis E,
Gustafson S, Handy B, Katus H, Melanson SE, Panteghini M, Venge P, Zorn M,
Jarolim P, Bruton D, Jarausch J, Jaffe AS.

Department of Laboratory Medicine and Pathology, Hilton 3, Mayo Clinic, 200 First
St. SW, Rochester, MN 55905, USA. saenger.amy@mayo.edu

BACKGROUND: High-sensitivity cardiac troponin assays are being introduced
clinically for earlier diagnosis of acute myocardial infarction (AMI). We
evaluated the analytical performance of a high-sensitivity cardiac troponin T
assay (hscTnT, Roche Diagnostics) in a multicenter, international trial.
METHODS: Three US and 5 European sites evaluated hscTnT on the Modular® Analytics
E170, cobas® 6000, Elecsys 2010, and cobas® e 411. Precision, accuracy,
reportable range, an inter-laboratory comparison trial, and the 99th percentile
of a reference population were assessed.
RESULTS: Total imprecision (CVs) were 4.6-36.8% between 3.4 and 10.3 ng/L hscTnT.
Assay linearity was up to 10,000 ng/L and the limit of blank and detection were 3
and 5 ng/L, respectively. The 99th percentile reference limit was 14.2 ng/L
(n=533). No significant differences between specimen types, assay incubation
time, or reagent lots existed. A substantial positive bias (76%) exists between
the 4th generation and hscTnT assays at the low end of the measuring range (<50
ng/L). hscTnT serum pool concentrations were within 2SD limits of the mean of
means in the comparison trial, indicating comparable results across multiple
platforms and laboratories.
CONCLUSION: The Roche hscTnT assay conforms to guideline precision requirements
and will likely identify additional patients with myocardial injury suspicious
for AMI.

11. Circulation. 2011 Jan 4;123(1):e3; author reply e4.

Letter by Lippi and Cervellin regarding article, "High-sensitivity troponin T
concentrations in acute chest pain patients evaluated with cardiac computed
tomography".

Lippi G, Cervellin G.

Comment on
    Circulation. 2010 Mar 16;121(10):1227-34.

12. Anesthesiology. 2011 Jan;114(1):58-69.

Preoperative cerebral oxygen saturation and clinical outcomes in cardiac surgery.

Heringlake M, Garbers C, Käbler JH, Anderson I, Heinze H, Schön J, Berger KU,
Dibbelt L, Sievers HH, Hanke T.

Cardiac Anesthesia Unit, Department of Anesthesiology, University of Lübeck,
Lübeck, Germany. heringlake@t-online.de

Comment in
    Anesthesiology. 2011 Jan;114(1):12-3.

BACKGROUND: The current study was designed to determine the relation between
preoperative cerebral oxygen saturation (Sco2), variables of cardiopulmonary
function, mortality, and morbidity in a heterogeneous cohort of cardiac surgery
patients.
METHODS: In this study, 1,178 consecutive patients scheduled for on-pump surgery
were prospectively studied. Preoperative Sco2, demographics, N-terminal
pro-B-type natriuretic peptide, high-sensitive troponin T, clinical outcomes, and
30-day and 1-yr mortality were recorded.
RESULTS: Median additive EuroSCORE was 5 (range: 0-19). Thirty-day and 1-yr
mortality and major morbidity (at least two major complications and/or a
high-dependency unit stay of at least 10 days) were 3.5%, 7.7%, and 13.3%,
respectively. Median minimal preoperative oxygen supplemented Sco2 (Sco2min-ox)
was 64% (range: 15-92%). Sco2min-ox was correlated (all: P value <0.0001) with
N-terminal pro-B-type natriuretic peptide (ρ: -0.35), high-sensitive troponin T
(ρ: -0.28), hematocrit (ρ: 0.34), glomerular filtration rate (ρ: 0.19), EuroSCORE
(τ: 0.20), and left ventricular ejection fraction class (τ: 0.12). Thirty-day
nonsurvivors had a lower Sco2min-ox than survivors (median 58% [95% CI, 50.7-62%]
vs. 64% [95% CI, 64-65%]; P < 0.0001). Receiver-operating curve analysis of
Sco2min-ox and 30-day mortality revealed an area-under-the-curve of 0.71 (95% CI,
0.68-0.73%; P < 0.0001) in the total cohort and an area-under-the-curve of 0.77
(95% CI, 0.69-0.86%; P < 0.0001) in patients with a EuroSCORE more than 10.
Logistic regression based on different EuroSCORE categories (0-2; 3-5, 6-10,
>10), Sco2min-ox, and duration of cardiopulmonary bypass showed that a Sco2min-ox
equal or less than 50% is an independent risk factor for 30-day and 1-yr
mortality.
CONCLUSIONS: Preoperative Sco2 levels are reflective of the severity of
cardiopulmonary dysfunction, associated with short- and long-term mortality and
morbidity, and may add to preoperative risk stratification in patients undergoing
cardiac surgery.

13. Circ J. 2011 Mar;75(3):656-61. Epub 2010 Dec 17.

Prognostic role of high-sensitivity cardiac troponin T in patients with
nonischemic dilated cardiomyopathy.

Kawahara C, Tsutamoto T, Nishiyama K, Yamaji M, Sakai H, Fujii M, Yamamoto T,
Horie M.

Cardiovascular and Respiratory Medicine, Shiga University of Medical Science,
Otsu, Japan.

Comment in
    Circ J. 2011 Mar;75(3):542-3.

BACKGROUND: Cardiac troponin T (cTnT) is useful biomarker in patients with
chronic heart failure (CHF). However, its clinical use is limited by the low
sensitivity of the conventional commercial assay system. Recently, a highly
sensitive cTnT (hs-cTnT) assay has become commercially available.
METHODS AND RESULTS: To compare the prognostic value of conventional cTnT and
hs-cTnT in patients with nonischemic dilated cardiomyopathy (DCM), hemodynamic
parameters and the serum levels of conventional cTnT, hs-cTnT and brain
natriuretic peptide (BNP) were measured in 85 consecutive CHF patients with
nonischemic DCM and then these patients were followed for a mean of 4.1 years.
During long-term follow up, there were 20 cardiac deaths. In 85 DCM patients,
conventional cTnT was elevated (≥0.03ng/ml) in 4 patients (5%) and hs-cTnT was
elevated (≥0.01ng/ml) in 46 patients (54%). In non-survivors (n=20), conventional
cTnT was elevated (≥0.03ng/ml) in 2 patients (2%) and hs-cTnT was elevated
(≥0.01ng/ml) in 17 patients (85%). In the stepwise multivariate analyses, a high
plasma level of BNP (P=0.002), low left ventricular ejection fraction (<30%,
P=0.012) and high hs-cTnT (≥0.01ng/ml, P=0.006) were independent significant
prognostic predictors, but conventional cTnT (≥0.03ng/ml) was not.
CONCLUSIONS: The findings of the present study indicated that a high serum
concentration of hs-cTnT is a useful prognostic predictor that is independent of
LVEF or BNP in CHF patients with non-ischemic DCM, suggesting that an increased
hs-cTnT concentration sensitively reflects ongoing myocardial damage.

14. Coron Artery Dis. 2011 Mar;22(1):87-91.

Effects of loading dose of atorvastatin before percutaneous coronary intervention
on periprocedural myocardial injury.

Yu XL, Zhang HJ, Ren SD, Geng J, Wu TT, Chen WQ, Ji XP, Zhong L, Ge ZM.

Department of Cardiology, Qilu Hospital, Shandong University, Key Laboratory of
Cardiovascular Remodeling and Function Research, Chinese Ministry of Education
and Chinese Ministry of Public Health, Jinan, PR China.

OBJECTIVES: To investigate the effects of loading dose of atorvastatin on
periprocedural myocardial injury and inflammatory reaction in patients with
non-ST segment elevation (NSTE) acute coronary syndromes (unstable angina or NSTE
acute myocardial infarction).
METHODS: A total of 81 patients with NSTE-acute coronary syndromes were randomly
divided into the pretreatment with atorvastatin group [80 mg 12 h before
percutaneous coronary intervention (PCI), with a further 40 mg preprocedure dose]
(n=41) or the placebo group (n=40). The main end point was a 30-day incidence of
major adverse cardiac events (cardiac death, nonfatal acute myocardial
infarction, or revascularization with either PCI or coronary artery bypass
grafting). Creatine kinase-MB, cardiac troponin I, and high-sensitivity
C-reactive protein levels were measured at the baseline and at 8 and 24 h after
the procedure.
RESULTS: Major adverse cardiac events occurred in 2.4% of patients in the
atorvastatin group and 22.5% of those in the placebo group (P=0.0161). This
difference was mostly because of reduction in the incidence of myocardial
infarction (2.4 vs. 20.0%; P=0.0307). Markers of the two groups were elevated
after PCI; however, the higher values of creatine kinase-MB, cardiac troponin I,
and high-sensitivity C-reactive protein in the atorvastatin treatment group were
significantly lower than those in the placebo group (P<0.01).
CONCLUSION: Short-term pretreatment with a high dose of atorvastatin
significantly reduces procedural myocardial injury in early PCI.

15. Am Heart J. 2011 Jan;161(1):68-75.

Prognostic value of sensitive troponin T in patients with stable and unstable
angina and undetectable conventional troponin.

Ndrepepa G, Braun S, Mehilli J, Birkmeier KA, Byrne RA, Ott I, Hösl K, Schulz S,
Fusaro M, Pache J, Hausleiter J, Laugwitz KL, Massberg S, Seyfarth M, Schömig A,
Kastrati A.

Deutsches Herzzentrum, Technische Universität, Munich, Germany.

Comment in
    Am Heart J. 2011 May;161(5):e33; author reply e35.

BACKGROUND: high-sensitivity cardiac troponin assays enable the measurement of
cardiac troponin concentrations in the majority of patients with coronary artery
disease. The objective of this study was to investigate the prognostic value of
sensitive cardiac troponin in patients with stable and unstable angina presenting
with undetectable levels of conventional troponin.
METHODS: this study included 1,057 patients with stable (808 patients) or
unstable (249 patients) angina who presented with undetectable conventional
cardiac troponin T and underwent coronary artery revascularization. The cardiac
troponin T was measured with conventional and high-sensitivity assays, in
parallel, using the same plasma sample. The primary end point was 4-year
mortality.
RESULTS: the total sensitive troponin T level (median [interquartile range]) was
0.008 (0.005-0.014) microg/L. Variables independently associated with an elevated
level of sensitive troponin T were elderly age, male sex, higher body mass index,
presence of diabetes, unstable angina, increased New York Heart Association
class, reduced left ventricular ejection fraction, elevated level of N-terminal
pro-brain natriuretic peptide, reduced glomerular filtration rate, and elevated
level of C-reactive protein. During the follow-up period, there were 83 deaths.
The sensitive troponin T level was an independent predictor of 4-year mortality
(adjusted hazard ratio = 1.47 with 95% CI 1.17-1.84, P < .001 for each unit
increase in the natural logarithm of the sensitive troponin T).
CONCLUSIONS: the elevated levels of sensitive cardiac troponin T in patients with
stable or unstable angina presenting with undetectable conventional cardiac
troponin T are significantly associated with reduced survival.

16. Eur J Heart Fail. 2011 Jan;13(1):37-42. Epub 2010 Dec 13.

Serial changes in high-sensitive troponin I predict outcome in patients with
decompensated heart failure.

Xue Y, Clopton P, Peacock WF, Maisel AS.

Department of Medicine, University of California at San Diego, 200 West Arbor
Drive, San Diego, CA 92103, USA. yxue100@yahoo.com

AIMS: The aim of this study was to evaluate the prognostic utility of small
troponin I (TnI) elevations, serial TnI measurements, and the combination of TnI
and brain natriuretic peptide (BNP) in patients with decompensated heart failure
(HF).
METHODS AND RESULTS: One hundred and forty-four patients with acute HF were
followed from admission to 90 days post-discharge. Primary endpoints were all
cause mortality and HF-related readmission. Troponin I and BNP levels were
checked on admission, discharge, and up to four consecutive days during
hospitalization. A discharge TnI cut-off of 23.25 ng/L and discharge BNP cut-off
of 360 ng/L were determined by receiver operator characteristic (ROC). Troponin I
above 23.25 ng/L is associated with increased risk for mortality and readmission
(P = 0.003). Comparing with TnI quartile 1, TnI quartiles 2-4 had increased
mortality and readmission, P = 0.019, P = 0.007, P = 0.014, respectively.
Compared with patients with low TnI+low BNP, increased mortality and readmission
were seen in patients with high TnI+high BNP (P = 0.007), high TnI+low BNP (P =
0.015), and low TnI+high BNP (P = 0.042). Patients with increasing TnI during
treatment had increased mortality compared with patients with stable or
decreasing TnI (P = 0.047). In multivariate analysis, TnI reached statistical
significance (P = 0.009), while BNP did not.
CONCLUSION: This study demonstrates that very small TnI elevations and BNP
elevations are associated with increased 90-day mortality and readmission. When
compared by ROC and multivariate analysis, TnI is as good a predictor of
mortality and readmission as BNP if not slightly better. Patients with increasing
TnI during hospitalization for acute HF had increased risk for 90-day mortality.

17. Am Heart J. 2010 Dec;160(6):e47; author reply e49.

Elevation of high-sensitivity cardiac troponin T and composite end points in
randomized trials.

Lozano I, Barriales V, Rondan J, Suarez C.

Comment on
    Am Heart J. 2010 Jun;159(6):972-8.

PMID: 21146648  [PubMed - indexed for MEDLINE]

18. Biomark Med. 2010 Dec;4(6):889-94.

A window into your heart: taking cardiac troponin to the next level.

Hallén J, Atar D.

Department of Cardiology, Oslo University Hospital, Aker & Ullevål, Oslo, Norway.
jonashallen@gmail.com

The cardiac troponins are important cardiovascular biomarkers for myocardial
necrosis and are measured in thousands of patients daily. In parallel with the
widespread adoption of troponin testing for the diagnosis of myocardial
infarction during the last two decades, the analytical sensitivity of assays has
progressively improved, which has allowed the identification of more acute
coronary syndrome patients at risk of future cardiac events. In addition, using
novel high-sensitivity assays, circulating troponin can be observed not only in
acute settings, but also in many patients suffering from chronic diseases such as
coronary artery disease, heart failure and diabetes. We believe that these
findings provide a compelling case for exploring whether troponin levels may be a
useful tool for guiding clinical decision-making directly in the management of
some of these chronic conditions. Sampling of troponin in such patient
populations may allow for more refined risk stratification and, importantly, help
clinicians individualize care beyond what is currently possible.

19. J Thromb Haemost. 2011 Feb;9(2):410-2. doi: 10.1111/j.1538-7836.2010.04153.x.

Does high-sensitivity troponin measurement aid in the diagnosis of pulmonary
embolism?

Hogg K, Haslam S, Hinchliffe E, Sellar L, Lecky F, Cruickshank K.

20. J Am Coll Cardiol. 2010 Nov 30;56(23):1922-9.

Timing of pre-operative Beta-blocker treatment in vascular surgery patients:
influence on post-operative outcome.

Flu WJ, van Kuijk JP, Chonchol M, Winkel TA, Verhagen HJ, Bax JJ, Poldermans D.

Department of Anesthesia, Erasmus Medical Center, Rotterdam, the Netherlands.

OBJECTIVES: This study evaluated timing of β-blocker initiation before surgery
and its relationship with: 1) pre-operative heart rate and high-sensitivity
C-reactive-protein (hs-CRP) levels; and 2) post-operative outcome.
BACKGROUND: Perioperative guidelines recommend β-blocker initiation days to weeks
before surgery, on the basis of expert opinions.
METHODS: In 940 vascular surgery patients, pre-operative heart rate and hs-CRP
levels were recorded, next to timing of β-blocker initiation before surgery (0 to
1, >1 to 4, >4 weeks). Pre- and post-operative troponin-T measurements and
electrocardiograms were performed routinely. End points were 30-day cardiac
events (composite of myocardial infarction and cardiac mortality) and long-term
mortality. Multivariate regression analyses, adjusted for cardiac risk factors,
evaluated the relation between duration of β-blocker treatment and outcome.
RESULTS: The β-blockers were initiated 0 to 1, >1 to 4, and >4 weeks before
surgery in 158 (17%), 393 (42%), and 389 (41%) patients, respectively. Median
heart rate at baseline was 74 (±17) beats/min, 70 (±16) beats/min, and 66 (±15)
beats/min (p < 0.001; comparing treatment initiation >1 with <1 week
pre-operatively), and hs-CRP was 4.9 (±7.5) mg/l, 4.1 (±.6.0) mg/l, and 4.5
(±6.3) mg/l (p = 0.782), respectively. Treatment initiated >1 to 4 or >4 weeks
before surgery was associated with a lower incidence of 30-day cardiac events
(odds ratio: 0.46, 95% confidence interval [CI]: 0.27 to 0.76, odds ratio: 0.48,
95% CI: 0.29 to 0.79) and long-term mortality (hazard ratio: 0.52, 95% CI: 0.21
to 0.67, hazard ratio: 0.50, 95% CI: 0.25 to 0.71) compared with treatment
initiated <1 week pre-operatively.
CONCLUSIONS: Our results indicate that β-blocker treatment initiated >1 week
before surgery is associated with lower pre-operative heart rate and improved
outcome, compared with treatment initiated <1 week pre-operatively. No reduction
of median hs-CRP levels was observed in patients receiving β-blocker treatment >1
week compared with patients in whom treatment was initiated between 0 and 1 week
before surgery.

21. Ann Clin Biochem. 2011 Jan;48(Pt 1):38-40. Epub 2010 Nov 23.

High-sensitivity troponin T as a marker of myocardial injury after radiofrequency
catheter ablation.

Vasatova M, Pudil R, Tichy M, Buchler T, Horacek JM, Haman L, Parizek P, Palicka
V.

Institute of Clinical Biochemistry and Diagnostics, Charles University, Faculty
of Medicine, University Hospital, Hradec Kralove, Czech Republic.
ulrycmar@fnhk.cz

BACKGROUND: The aim of our study was to monitor radiofrequency catheter
ablation-induced myocardial damage by measuring high-sensitivity cardiac troponin
T (hs-cTnT).
METHODS: Serum concentrations of hs-cTnT (Elecsys 2010 system, Roche) were
measured in 73 healthy blood donors and serially in 27 patients who had samples
taken both before and 24 h after radiofrequency ablation (RFA) for
atrioventricular nodal re-entry tachycardia (AVNRT), atrial fibrillation (AF) or
right atrial flutter (AFL).
RESULTS: Significant increases of hs-cTnT were seen in patients after RFA (AVNRT:
P = 0.0115, AF: P = 0.0011, AFL: P = 0.0009). Postprocedural serum hs-cTnT
correlated with the number of radiofrequency applications and with the duration
of RFA procedure. Spearman's coefficient of rank correlation (r) were as follows:
hs-cTnT versus RFA duration: r = 0.771 (P < 0.001); hs-cTnT versus number of
pulses: r = 0.708 (P < 0.001). Patients with the diagnosis of AVNRT had lower
serum hs-cTnT concentration after RFA compared with AFL (P < 0.0001) and AF (P <
0.0001) patients.
CONCLUSIONS: Our data indicate that RFA causes a significant increase of serum
hs-cTnT concentration that could be used to monitor myocardial injury.

22. Circulation. 2010 Dec 7;122(23):2411-8. Epub 2010 Nov 22.

The sPLA2 Inhibition to Decrease Enzyme Release after Percutaneous Coronary
Intervention (SPIDER-PCI) trial.

Džavík V, Lavi S, Thorpe K, Yip PM, Plante S, Ing D, Overgaard CB, Osten MD, Lan
J, Robbins K, Miner SE, Horlick EM, Cantor WJ.

Interventional Cardiology Program, Division of Cardiology, Peter Munk Cardiac
Centre, University Health Network, Toronto, Ontario, Canada.
vlad.dzavik@uhn.on.ca

BACKGROUND: Secretory phospholipase A(2) (sPLA(2)) may play a role in myonecrosis
after elective percutaneous coronary intervention (PCI). Inhibition of this
enzyme may have a beneficial effect. The central hypothesis of this study was
that treatment with varespladib, a small-molecule inhibitor of sPLA(2) would
reduce postprocedural release of cardiac biomarkers after elective percutaneous
coronary intervention.
METHODS AND RESULTS: Between October 2007 and June 2009, 144 stable patients were
randomized in a phase II trial to receive varespladib 500 mg PO BID or placebo 3
to 5 days before and for 5 days after elective percutaneous coronary
intervention. The primary end point was elevation of troponin I or creatine
kinase-MB above the upper limit of normal at 6 to 8 or 18 to 24 hours after
percutaneous coronary intervention. Mean age was 63±10 and 64±10 years, with 38%
and 42% with diabetes mellitus and 29% and 28% with prior myocardial infarction
for the varespladib and placebo groups, respectively. The primary end point
occurred in 75% of varespladib and 63% of placebo patients (P=0.14). Troponin I 3
times the upper limit of normal was observed in 57% and 50% (P=0.39) and creatine
kinase-MB 2 times the upper limit of normal in 14% and 3% (P=0.018). Median
(first and third quartiles) change in high-sensitivity C-reactive protein in
these 2 groups was 0.65 mg/L (-0.18 and 1.48) and 0.70 mg/L (0.00 and 1.50) at 18
to 24 hours (P=0.81) and 0.20 mg/L (-0.70 and 1.40) and 0.60 mg/L (-0.12 and
1.72) at 3 to 5 days (P=0.23), whereas change in sPLA(2) activity at 3 to 5 days
in a subset was -2.85 ng/ml (-3.40 and -1.85) and 0.25 ng/ml (-0.20 and 0.85)
(P<0.001).
CONCLUSIONS: Inhibition of sPLA(2) by varespladib administered for 3 to 5 days
before the procedure does not reduce periprocedural myonecrosis associated with
elective percutaneous coronary intervention.
CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique
identifier: NCT00533039.

23. Clin Chem Lab Med. 2011 Feb;49(2):335-6. Epub 2010 Nov 16.

Stability of serum samples and hemolysis interference on the high sensitivity
troponin T assay.

Li A, Brattsand G.

24. CMAJ. 2010 Nov 9;182(16):1761.

High sensitivity cardiac troponin testing.

Kavsak PA, McQueen MJ.

Comment on
    CMAJ. 2010 Sep 7;182(12):1295-300.

25. J Intern Med. 2011 Feb;269(2):160-71. doi: 10.1111/j.1365-2796.2010.02287.x. Epub
2010 Oct 22.

Circulating cardiovascular biomarkers in recurrent atrial fibrillation: data from
the GISSI-atrial fibrillation trial.

Latini R, Masson S, Pirelli S, Barlera S, Pulitano G, Carbonieri E, Gulizia M,
Vago T, Favero C, Zdunek D, Struck J, Staszewsky L, Maggioni AP, Franzosi MG,
Disertori M; on the behalf of the GISSI-AF Investigators.

Istituto di Ricerche Farmacologiche "Mario Negri", Milan Istituti Ospitalieri,
Cremona POL Madonna della Consolazione, Reggio Calabria, Italy.
roberto.latini@marionegri.it

OBJECTIVE: we evaluated the prognostic role of circulating cardiovascular
biomarkers in patients with a history of recent atrial fibrillation (AF).
BACKGROUND: predicting long-term maintenance of sinus rhythm in patients with AF
is difficult.
METHODS: plasma concentrations of three specific cardiac markers
[high-sensitivity troponin T (hsTnT), N-terminal probrain natriuretic peptide
(NT-proBNP) and mid-regional proatrial natriuretic peptide (MR-proANP)] and three
stable fragments of vasoactive peptides [mid-regional proadrenomedullin
(MR-proADM), copeptin (CT-proAVP) and CT-proendothelin-1 (CT-proET-1)] were
measured at baseline and after 6 and 12 months in 382 patients enrolled in the
GISSI-AF study, a prospective randomized trial to determine the effect of
valsartan to reduce the recurrence of AF. The association between these markers,
clinical characteristics and recurrence of AF was tested by univariate and
multivariate Cox models.
RESULTS: mean patient age was 68 ± 9 years (37.2% females). A total of 84.8% of
patients had a history of hypertension. In total, 59.7% qualified for history of
AF because of successful cardioversion, 11.8% because of two or more episodes of
AF in the 6 months preceding randomization and 28.5% because of both. Patients in
AF at 6 or 12 months (203 (53.1%) with first recurrence) had significantly higher
concentrations of most biomarkers. Despite low baseline levels, higher
concentrations of hsTnT {adjusted hazard ratio (HR) [95% confidence intervals
(CIs) for 1 SD increment] (1.15 [1.04-1.28], P = 0.007), MR-proANP (1.15
[1.01-1.30], P = 0.04), NT-proBNP (1.24 [1.11-1.39], P = 0.0001) and CT-proET-1
(1.16 [1.01-1.33], P = 0.03) independently predicted higher risk of a first
recurrence of AF. Changes over time of MR-proANP tended to predict subsequent
recurrence (adjusted HR [95%CI]) (1.53 [0.98-2.37], P = 0.06).
CONCLUSION: circulating markers of cardiomyocyte injury/strain and endothelin are
related to recurrence of AF in patients in sinus rhythm with a history of recent
AF.

26. Clin Chem. 2010 Dec;56(12):1902-4. Epub 2010 Oct 12.

Increasing cardiac troponin changes measured by a research high-sensitivity
troponin I assay: absolute vs percentage changes and long-term outcomes in a
chest pain cohort.

Kavsak PA, Ko DT, Wang X, Macrae AR, Jaffe AS.

Comment on
    Clin Chem. 2010 Apr;56(4):642-50.
    Clin Chem. 2010 Mar;56(3):487-9.

27. Intensive Care Med. 2011 Jan;37(1):77-85. Epub 2010 Oct 12.

Circulating high sensitivity troponin T in severe sepsis and septic shock:
distribution, associated factors, and relation to outcome.

Røsjø H, Varpula M, Hagve TA, Karlsson S, Ruokonen E, Pettilä V, Omland T;
FINNSEPSIS Study Group.

Collaborators: Lund V, Suvela M, Laru-Sompa R, Laine H, Karlsson S, Saarinen K,
Hovilehto S, Loisa P, Korhonen T, Kairi P, Alaspää A, Kiviniemi O, Kaminski T,
Pentti J, Alila S, Pettilä V, Varpula M, Hynninen M, Varpula T, Linko R, Ruokonen
E, Arvola P, Parviainen I, Ala-Kokko T, Heikkinen J.

Division of Medicine, Akershus University Hospital, Sykehusveien 27, 1478
Lørenskog, Norway.

PURPOSE: To assess the clinical utility of a recently developed highly sensitive
cardiac troponin T (hs-cTnT) assay for providing prognostic information on
patients with sepsis.
METHODS: cTnT levels were measured by the novel hs-cTnT assay at two time points
(inclusion and 72 h thereafter) in a subgroup of patients from the FINNSEPSIS
study and associations with clinical outcomes were examined. Results for the
hs-cTnT assay were compared to those of the established fourth-generation cTnT
assay.
RESULTS: cTnT measured by the fourth-generation and hs-cTnT assay was detectable
in 124 (60%) and 207 (100%) patients, respectively, on inclusion in this study.
hs-cTnT levels on inclusion correlated with several indices of risk in sepsis,
including the simplified acute physiology score (SAPS) II and sequential organ
failure assessment (SOFA) scores. The level of hs-cTnT on inclusion was higher in
hospital non-survivors (n = 47) than survivors (n = 160) (median 0.054 [Q1-3,
0.022-0.227] versus 0.035 [0.015-0.111] μg/L, P = 0.047), but hs-cTnT level was
not an independent predictor of in-hospital mortality. hs-cTnT levels on
inclusion were also higher in patients with septic shock during the
hospitalization (0.044 [0.024-0.171] versus 0.033 [0.012-0.103] μg/L, P = 0.03),
while this was not the case for the fourth-generation cTnT assay or NT-proBNP
levels.
CONCLUSIONS: Circulating hs-cTnT is present in patients with severe sepsis and
septic shock, associates with disease severity and survival, but does not add to
SAPS II score for prediction of mortality. hs-cTnT measurement could still have a
role in sepsis as an early marker of shock.

28. Am Heart J. 2010 Oct;160(4):583-94.

Novel biomarkers in cardiovascular disease: update 2010.

Hochholzer W, Morrow DA, Giugliano RP.

TIMI Study Group, Cardiovascular Division, Department of Medicine, Brigham and
Women's Hospital, Harvard Medical School, Boston, MA, USA.

The rapid evaluation of patients presenting with symptoms suggestive of an acute
coronary syndrome is of great clinical relevance. Biomarkers have become
increasingly important in this setting to supplement electrocardiographic
findings and patient history because one or both can be misleading. Today,
cardiac troponin is still the only marker used routinely in this setting due to
its myocardial tissue specificity and sensitivity, as well as its established
usefulness for therapeutic decision making. However, even current generation
troponin assays have certain limitations such as insufficient sensitivity for
diagnosing unstable angina. Novel high-sensitivity assays for cardiac troponin
have the potential to overcome these limitations. Further studies are needed to
answer some critical questions regarding the best cutoffs for diagnosis and risk
assessment and the optimal work-up for rule-out of acute myocardial infarction.
Other nonmyocardial tissue-specific markers might help in this setting.
Myeloperoxidase, copeptin, and growth differentiation factor 15 reflect different
aspects of the development of atherosclerosis or acute ischemia. Each has
demonstrated impact in risk stratification of acute coronary syndromes. Limited
data also show that copeptin may, when used together with cardiac troponin,
improve the sensitivity for diagnosing acute myocardial infarction, and growth
differentiation factor 15 may help in selection of patients that benefit from
invasive therapy. Further evaluation is needed before these markers can be
adopted routinely in clinical practice.

29. Am J Med. 2010 Dec;123(12):1134-42.

Implementation of high sensitivity cardiac troponin T measurement in the
emergency department.

Christ M, Popp S, Pohlmann H, Poravas M, Umarov D, Bach R, Bertsch T.

Department of Emergency and Critical Care Medicine, City Hospital Nuremberg,
Nuremberg, Germany. michael.christ@klinikum-nuernberg.de

BACKGROUND: we examined the diagnostic performance of high sensitivity cardiac
troponin T (cTnThs) measurement and its ability to predict risk in unselected
patients presenting to the emergency department with acute chest pain.
METHODS: we conducted a retrospective analysis of 137 consecutive patients with
chest pain (age range, 66 ± 16 years; 64% male). A final diagnosis of acute
myocardial infarction was made using the "old" (cTnT fourth-generation assay, ≥
0.04 microg/L) or the "new" cutpoint (cTnThs ≥ 0.014 microg/L).
RESULTS: the adjudicated final diagnosis of acute myocardial infarction
significantly increased from 20 to 35 patients (a 75% increase) and
troponin-positive nonvascular cardiac chest pain from 10 to 30 (a 200% increase)
using cTnThs. The number of patients with unstable angina or troponin-negative
nonvascular cardiac chest pain significantly decreased (P <.05). Diagnostic
performance of cTnThs levels at admission was significantly higher compared to
cTnT levels (area under the curve [AUC] 0.85 vs AUC 0.70; P <.05). cTnThs levels
below the detection limit (<0.003 microg/L) had a negative predictive value of
100% to exclude acute myocardial infarction. The event rate during 6 months of
follow-up was low in patients with cTnThs levels <0.014 microg/L, while patients
with cTnT levels ≥ 0.04 μg/L were at increased, and patients with cTnThs ≥ 0.014
μg/L and cTnT <0.04 microg/L at intermediate risk of death or recurrent
myocardial infarction (P = .002). Risk was highest in chest pain patients with
dynamic changes of cTnThs levels >30%.
CONCLUSION: the introduction of cTnThs assay displays an excellent diagnostic
performance for the workup of patients with chest pain at the time of their
initial presentation. Even small increases of cTnThs indicate increased risk for
death or myocardial infarction during follow-up.

30. Heart. 2011 May;97(10):823-31. Epub 2010 Sep 30.

Determinants of troponin release in patients with stable coronary artery disease:
insights from CT angiography characteristics of atherosclerotic plaque.

Korosoglou G, Lehrke S, Mueller D, Hosch W, Kauczor HU, Humpert PM, Giannitsis E,
Katus HA.

University of Heidelberg, Department of Cardiology, Im Neuenheimer Feld 410,
Heidelberg, 69120, Germany. gkorosoglou@hotmail.com

Comment in
    Heart. 2011 May;97(10):785-6.

OBJECTIVE: To understand the determinants of troponin release in patients with
stable coronary artery disease (CAD) by comparing high sensitive troponin T
(hsTnT) levels with computed tomography angiography (CTA) characteristics of
atherosclerotic plaque.
METHODS: hsTnT was determined in 124 consecutive patients with stable angina, who
underwent clinically indicated 256-slice CTA for suspected CAD. CTA was used to
assess (1) coronary calcification; (2) stenosis severity; (3) non-calcified
plaque volume; (4) plaque composition (soft or mixed, described as
'non-calcified' versus calcified) and (5) the presence of vascular remodeling in
areas of non-calcified plaque.
RESULTS: All CT scans were performed without adverse events, and diagnostic image
quality was achieved in 1830/1848 available coronary segments (99.0%). In 29/124
patients, hsTnT was ≥14 pg/ml (range 14.0-34.4). Weak, albeit significant,
correlations were found between hsTnT and calcium scoring (r=0.45, p<0.001),
while a stronger correlation was found between hsTnT and the total non-calcified
plaque burden (r=0.79, p<0.001). Patients with non-calcified plaque (n=44)
yielded significantly higher hsTnT values than those with normal vessels (n=46)
or those with only calcified lesions (n=26), (12.6 ± 5.2 vs 8.3 ± 2.6 and 8.8 ±
3.0 pg/ml, respectively, p<0.001). Furthermore, those with remodeled
non-calcified plaque (n=8) showed even higher hsTnT values of 26.3 ± 6.5 pg/ml
than all other groups (p<0.001). This allowed the identification of patients with
remodeled non-calcified plaque by hsTnT with high accuracy (area under the
curve=0.90, SE=0.07, 95% CI 0.84 to 0.95).
CONCLUSIONS: Chronic clinically silent rupture of non-calcified plaque with
subsequent microembolisation may be a potential source of troponin elevation. In
light of recent imaging studies, in which patients with positively remodeled
non-calcified plaque were shown to be at high risk for developing acute coronary
syndromes, hsTnT may serve as a biomarker for such 'vulnerable' coronary lesions
even in presumably stable CAD.

31. Clin J Am Soc Nephrol. 2011 Jan;6(1):133-41. Epub 2010 Sep 28.

Circulating endotoxemia: a novel factor in systemic inflammation and
cardiovascular disease in chronic kidney disease.

McIntyre CW, Harrison LE, Eldehni MT, Jefferies HJ, Szeto CC, John SG, Sigrist
MK, Burton JO, Hothi D, Korsheed S, Owen PJ, Lai KB, Li PK.

Department of Renal Medicine, Royal Derby Hospital, Uttoxeter Road, Derby, DE22
3NE, United Kingdom. chris.mcintyre@nottingham.ac.uk

BACKGROUND AND OBJECTIVES: Translocated endotoxin derived from intestinal
bacteria has a wide range of adverse effects on cardiovascular (CV) structure and
function, driving systemic inflammation, atherosclerosis and oxidative stress.
This study's aim was to investigate endotoxemia across the spectrum of chronic
kidney disease (CKD).
DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Circulating endotoxin was measured
in 249 patients comprising CKD stage 3 to 5 and a comparator cohort of
hypertensive patients without significant renal impairment. Patients underwent
extended CV assessment, including pulse wave velocity and vascular calcification.
Hemodialysis (HD) patients also received detailed echocardiographic-based
intradialytic assessments. Patients were followed up for 1 year to assess
survival.
RESULTS: Circulating endotoxemia was most notable in those with the highest CV
disease burden (increasing with CKD stage), and a sharp increase was observed
after initiation of HD. In HD patients, predialysis endotoxin correlated with
dialysis-induced hemodynamic stress (ultrafiltration volume, relative
hypotension), myocardial stunning, serum cardiac troponin T, and high-sensitivity
C-reactive protein. Endotoxemia was associated with risk of mortality.
CONCLUSIONS: CKD patients are characteristically exposed to significant
endotoxemia. In particular, HD-induced systemic circulatory stress and recurrent
regional ischemia may lead to increased endotoxin translocation from the gut.
Resultant endotoxemia is associated with systemic inflammation, markers of
malnutrition, cardiac injury, and reduced survival. This represents a crucial
missing link in understanding the pathophysiology of the grossly elevated CV
disease risk in CKD patients, highlighting the potential toxicity of conventional
HD and providing a novel set of potential therapeutic strategies to reduce CV
mortality in CKD patients.

32. Biosens Bioelectron. 2010 Nov 15;26(3):1062-7. Epub 2010 Aug 21.

Disposable immunosensor for human cardiac troponin T based on
streptavidin-microsphere modified screen-printed electrode.

Silva BV, Cavalcanti IT, Mattos AB, Moura P, Sotomayor Mdel P, Dutra RF.

Laboratório de Pesquisa em Diagnóstico/LAPED, Pronto Socorro Cardiológico de
Pernambuco/PROCAPE, Universidade de Pernambuco, Rua dos Palmares, s/n, 50100-130
Recife-PE, Brazil.

Screen-printed electrodes (SPE) have been widely used in the design of disposable
sensors bringing advances in the use of electrochemical immunosensors for in
field-clinical analysis. In this work, streptavidin polystyrene microspheres were
incorporated to the electrode surface of SPEs in order to increase the analytical
response of the cardiac troponin T (cTnT), a specific biomarker for the acute
myocardial infarction diagnosis. The precise calculation of the stoichiometric
streptavidin-biotin ratio [1:4] allowed the increase of sensitivity and stability
of the immunosensor response to the cTnT analyte. The surface of the immunosensor
was characterized by scanning electron microscopy and cyclic voltammetry. It was
observed that the use of streptavidin microspheres significantly increased the
analytical sensitivity of the electrode in 8.5 times, showing a curve with a
linear response range between 0.1 and 10 ngmL(-1) of cTnT and a detection limit
of 0.2 ngmL(-1). The proposed SPE showed ease preparation and high sensitivity
allowing the detection of cTnT in the range of clinical levels. The new device
coupled with a portable electrochemical analyzer shows great promise for
point-of-care quantitative testing of necrosis cardiac proteins.

33. Vasc Health Risk Manag. 2010 Sep 7;6:691-9.

The utility of troponin measurement to detect myocardial infarction: review of
the current findings.

Daubert MA, Jeremias A.

Division of Cardiovascular Medicine, Department of Internal Medicine, Stony Brook
University Medical Center, Stony Brook, NY 11794, USA.

Myocardial infarction (MI) is defined by the presence of myocardial necrosis in
combination with clinical evidence of myocardial ischemia. Cardiac troponins are
regulatory proteins within the myocardium that are released into the circulation
when damage to the myocyte has occurred. Therefore, serum troponin is an
exquisitely sensitive marker of myocardial injury and is necessary for
establishing the diagnosis of MI. High-sensitivity troponin assays are improving
the diagnostic accuracy and rapid detection of myocardial infarction. The early
identification of MI is vital for the institution of anti-thrombotic therapy to
limit myocardial damage and preserve cardiac function. Troponin has both
diagnostic and prognostic significance in the setting of acute coronary syndrome
(ACS). Increased troponin levels in the absence of ACS should prompt an
evaluation for an alternative, non-thrombotic mechanism of troponin elevation and
direct management at the underlying cause. This review describes the role of
troponin in the evaluation of patients with suspected myocardial infarction.

34. Clin Lab. 2010;56(7-8):355-8.

Conference on clinical use of troponin T high sensitive (TnThs) on September 8,
2009 at the airport conference center, Frankfurt/Main.

Bertsch T, Braun SL, Giannitis E, Knebel F, Weber M, Christ M.

Institut für Klinische Chemie, Laboratoriumsmedizin und Transfusionsmedizin,
Klinikum Nürnberg, Nürnberg, Germany. thomas.bertsch@klinikum-nuernberg.de

With the redefinition of myocardial infarction in 2000, cardiology associations
ESC and ACC require the use of the 99th percentile of a healthy population at a
coefficient of variation (CV) of less than 10 % for Troponin values in diagnosing
myocardial infarction. With a new Troponin T high sensitive (TnThs) assay as an
advancement, it is now possible to fulfill these requirements. A panel of experts
from laboratories and cardiologists discussed how to use this new assay in daily
routine. Their experience confirms the excellent correlation between the upper
measuring range of the new, highly sensitive Troponin T high sensitive test and
the values obtained for Troponin T (4th generation). The Troponin T high
sensitive test will identify more patients with myocardial infarction when using
Troponin Ths above the 99t percentile (14 pg/mL). To diagnose myocardial
infarction, one Troponin T value above the 99th percentile, a rise or fall within
hours, and symptoms of ischemia need to be applied. Patients with elevated
Troponin T levels but without myocardial infarction are supposed to have
myocardial damage due to other reasons and have a rather poor prognosis. Is one
of the criteria is not fulfilled, a myocardial infarction is less probable and
differential diagnosis needs to be conducted.

35. Circulation. 2010 Oct 5;122(14):1387-95. Epub 2010 Sep 20.

Serial measurement of growth-differentiation factor-15 in heart failure: relation
to disease severity and prognosis in the Valsartan Heart Failure Trial.

Anand IS, Kempf T, Rector TS, Tapken H, Allhoff T, Jantzen F, Kuskowski M, Cohn
JN, Drexler H, Wollert KC.

Cardiology 111-C, VA Medical Center, 1 Veterans Drive, Minneapolis, MN 55417,
USA. anand001@umn.edu

BACKGROUND: Growth-differentiation factor-15 (GDF-15) is emerging as a prognostic
biomarker in patients with coronary artery disease. Little is known about GDF-15
as a biomarker in patients with heart failure.
METHODS AND RESULTS: The circulating concentration of GDF-15 was measured at
baseline (n=1734) and at 12 months (n=1517) in patients randomized in the
Valsartan Heart Failure Trial (Val-HeFT). GDF-15 levels at baseline ranged from
259 to 25 637 ng/L and were abnormally high (>1200 ng/L) in 85% of patients.
Higher levels were associated with features of worse heart failure and biomarkers
of neurohormonal activation, inflammation, myocyte injury, and renal dysfunction.
Baseline GDF-15 levels (per 100 ng/L) were associated with the risks of mortality
(hazard ratio, 1.017; 95% confidence interval, 1.014 to 1.019; P<0.001) and first
morbid event (hazard ratio, 1.020; 95% confidence interval, 1.017 to 1.023;
P<0.001). In a comprehensive multiple-variable Cox regression model that included
clinical prognostic variables, B-type natriuretic peptide, high-sensitivity
C-reactive

Medication Errors in Critically Ill Adults: A Review of Direct Observation Evidence

                Panagiotis Kiekkas, RN, MSc, PhD,Mary Karga, RN, MSc, PhD, Chrisoula Lemonidou, RN, MSc, PhD, Diamanto Aretha, MD; Menelaos Karanikolas, MD, MPH

                                                                           American Journal of Critical Care. 2011;20(1):36-44

Abstract

Objective To systematically review clinical evidence gathered by direct observation of medication errors in adult patients in intensive care units.
Methods Articles published between 1985 and 2008 in English-language journals indexed by the Cumulative Index for Nursing and Allied Health Literature and PUBMED were searched for studies on medication errors made by intensive care unit nurses. Studies in which errors were detected via direct observation were included.
Results Six studies met the inclusion criteria, and error incidence varied considerably among them. Wrong dose, wrong administration time and rate, and dose omission were the most common errors. Antibiotics, electrolytes, and cardiovascular drugs were commonly associated with errors, but the evidence about factors contributing to errors was inconclusive. Increased monitoring was the most common consequence of medication errors, whereas life-threatening and fatal adverse events were rare.
Conclusions Identification of patterns and characteristics of medication errors can guide preventive interventions. Factors contributing to errors, as well as drugs and error types associated with severe adverse events, deserve further investigation.

Introduction

Although patient safety has always been a primary concern for health care professionals, it is mainly within the past decade that international reports have linked errors by medical-nursing personnel to adverse events and adverse outcomes for patients.^[1-3] This link is especially true in critical care, where nurses have to meet the demands of high-risk patients and administer a wide variety of pharmacological agents by multiple routes. The intensive care unit (ICU) is a complex environment, where the amount of cognitive information needed to reach a correct decision is high and often exceeds the upper limit of information that can be held in conscious memory.^[4] Beyond the complexity of the ICU environment, critically ill patients are particularly susceptible to the consequences of errors, as they may be unable to compensate for additional injury because of limited physiological reserve.^[5]

Medication errors have been defined as "preventable mistakes in prescribing or delivering medication to a patient, that is, an improper use of medicine or one that causes harm to a patient."^[6] Of importance, a medication error is independent of the occurrence of patient injury (or of the potential for injury).^[7] Although medication errors may occur at any stage of the medication process, most occur at the administration stage.^[8] Drug administration constitutes a high-responsibility, primary nursing task that can consume up to 40% of clinical nurses' work time.^[9] Errors associated with drugs can be particularly common in the ICU. Critically ill patients receive nearly twice as many medications as patients in general care units, and most medications involve calculations for bolus administration or continuous infusion.^[10,11]

Methods used for detecting medication errors vary. In a study where true medication errors in the ICU were recorded by an independent pharmacist, Flynn et al^[12] found that direct observation by trained personnel (mainly pharmacists) was significantly more valid and accurate than reviewing charts (by investigators) and incident self-reporting (by medicalnursing personnel). Comparison of the 3 error-detection methods revealed that 65.6% of true errors were detected via direct observation, whereas only 3.7% were detected via chart reviewing and 0.2% were detected via self-reporting of incidents. Error incidence could be underestimated because of unrecorded information in chart reviewing and because of subjective error assessment by untrained personnel in incident self-reporting.

The aim of this literature review was to synthesize the existing empirical evidence about medication errors occurring in adult ICU settings, focusing on the incidence, types, and clinical consequences of medication errors; drugs associated with medication errors; and factors contributing to medication errors. This review was limited to studies in which direct observation was used to detect medication errors, because that method is highly reliable for detecting errors.^[12]

Materials and Methods

Articles published between January 1985 and December 2008 in English-language journals indexed by the Cumulative Index for Nursing and Allied Health Literature (CINAHL) and PUBMED (National Library of Medicine) were systematically searched for clinical studies of medication errors in critically ill adult patients. Additional articles were retrieved from the reference lists of the articles found through the initial online search. A combination of the following terms was used in the search: errors, medication/drug errors, medication/drug safety, critical/intensive care unit, ICU/CCU, critically ill, and adult.

Specific criteria used to select studies for this review were as follows:

• Types of study settings: critical/intensive care settings for adult patients, that is, medical, surgical, or mixed ICUs. Studies conducted in pediatric or neonatal ICUs were excluded.
• Types of study design: prospective, single-center or multicenter, in which direct observation was used for data collection.
• Types of study subjects: nurses employed in ICUs.
• Types of exposure: medication errors occurring during drug prescription, preparation, dispensation, or administration. Studies in which medication errors were not separately reported (not distinguished from other error types) were excluded. Studies that included only medication errors that led to adverse events also were excluded (these errors may not have been representative of total medication errors).

Retrieved studies were screened for inclusion by 2 independent reviewers (P.K., M.K.) by using the titles and abstracts of the articles reporting the study results. When the reviewers disagreed about a particular study, a final determination was made jointly by both reviewers. Data extracted from selected studies were categorized according to the incidence, types and clinical consequences of medication errors, drugs associated with medication errors, and factors contributing to errors. Because the heterogeneous nature of these studies did not allow data to be combined in a meta-analysis, a narrative literature review was preferred.

Results

Study Characteristics and Design

A total of 6 studies^[13-18] were considered appropriate for this review. Three studies^[14,15,18] were conducted in the United States; the remaining studies were conducted in Iran,^[13] France,^[16] and the Netherlands. ^[17] Errors were detected during medication preparation and administration stages in 4 studies,^[13,16-18] during all stages of the medication process in 1 study,^[14] and only during administration of continuously infused drugs in 1 study.^[15]

First, Herout and Erstad^[15] focused on the administration of continuously infused drugs, whereas Kopp et al^[14] studied all stages of the medication process of both continuously infused and intermittently delivered drugs. Second, only Calabrese et al^[18] conducted a multicenter study, whereas van den Bemt et al^[17] studied 2 ICUs. Third, the duration of data collection varied considerably among studies, from 6 hours^[16] to 24 hours^[14] per day and from 5 days^[17] to 3 months^[18] total. Fourth, use of the disguised-observation technique minimizes the bias that could be induced by the observer's presence.^[19] Thus, the results of studies^[13,17,18] in which personnel were not informed about the exact observation aim may be more reliable. Fifth, in 5 studies, direct observation was conducted by pharmacists (Herout and Erstad^[15] did not report the observers' profession), who were ICUspecialized pharmacy residents in 2 studies,^[14,18] and trained in direct or disguised observation in another 2 studies.^[13,17] Sixth, in 3 studies,^[13,14,16] each pharmacist observed only 1 nurse. Finally, in 2 studies, only the most commonly used^[13] or high-risk medications^[18] were observed; thus error detection was limited to predefined drug categories.

Incidence and Types of Medication Errors

In all 6 studies, error incidence was estimated on the basis of drug observations and ranged from 3.3% to 72.5%. Error incidence was also estimated on the basis of opportunities for error (calculated by adding all steps for potential errors during drug preparation and administration) in 1 study.^[13]

Types of medication errors were reported in all 6 studies. In the studies where errors were observed during continuous drug infusion, wrong rate was reported in 4 studies and was the first,^[18] second,^[13] and third^[15] most common error type identified. Intermittently delivered drugs were administered intravenously, intramuscularly, subcutaneously, orally, or via nasogastric tube. Regarding errors associated with intermittently delivered drugs, wrong dose was reported in 5 studies and was the first,^[16] second,^[14] and third^[13,17] most common type of error reported. Wrong administration time was reported in 4 studies and was the first^[17] and third^[18] most common error type found. Dose omission was reported in 3 studies and was the first^[14] and second^[18] most common error type found. Wrong administration rate was reported in 2 studies and was the most common error type found.^[13]

Drugs Associated with Medication Errors

The drugs associated with medication errors were reported in 4 studies. In 2 studies,^[13,18] each drug was separately evaluated and the percentage of errors associated with each drug per number of observations of this drug was presented. Fahimi et al^[13] found that 4 antibiotics (amikacin, vancomycin, metronidazole, and ciprofloxacin) were included among the 7 drugs most associated with errors. Calabrese et al^[18] found that 3 cardiovascular drugs (epinephrine, digoxin, and norepinephrine) and 2 electrolytes (potassium chloride, magnesium) were included among the 6 drugs most associated with errors. In the other 2 studies,^[14,17] drugs were studied in categories. Van den Bemt et al^[17] found that only gastrointestinal drugs were significantly associated with more errors. Kopp et al^[14] presented the percentage of each drug category errors per total errors that could lead to adverse events. Cardiovascular drugs, antibiotics, sedatives/analgesics, and electrolytes were the drug categories most associated with errors.

Factors Contributing to Medication Errors

The factors contributing to medication errors were reported in 4 studies. Nursing distractions and workload peak, lack of drug knowledge, and communication deficiencies were the main factors associated with errors in 1 study each.^[13,14,17] Comparison of the ICUs of 2 different hospitals suggested that the presence of full-time specialized physicians and the use of drug preparation and administration protocols in 1 ICU may have contributed to fewer medication errors (compared with the other ICU, which had no full-time physicians or drug protocols). ^[17] Herout and Erstad^[15] found that unreliable measurements of patients' weights at admission were associated with wrong dose calculation of continuously infused drugs.

Clinical Consequences of Medication Errors

The clinical consequences of medication errors were reported in 4 studies. A potentially fatal case was reported in only 1 study.^[14] Potentially lifethreatening adverse events were reported in 2 studies, corresponding to 8.2% of medication errors leading to adverse events^[14] and to 19.7% of total medication errors.^[16] In 3 studies, 41.7%,^[16] 38.2%,^[17] and 2.7%^[18] of total medication errors led to the need for increased monitoring without temporary or permanent patient harm. In 1 study,^[18] 1.1% of medication errors led to the need for therapy or intervention, with temporary harm of the patient.

Discussion

In this review, we focused on studies of medication errors in the ICU detected via direct observation, rather than on studies of adverse drug events. Adverse drug events have a more random occurrence than medication errors and are less statistically predictable. It seems very difficult to predict whether a medication error will lead to an adverse event, and adverse drug events are not always attributed to medication errors (eg, adverse drug events can be due to unpredictable allergic reactions). Medication errors are not only more preventable than adverse drug events,^[16] but they also reveal weaknesses in the process of care. Thus medication errors are more reliable indicators of staff performance and quality of patient care than are adverse drug events.^[20] From a nursing perspective, detection of medication errors can provide a valuable insight into unsafe practices and help identify opportunities for improvement.

Besides their impact on patients' morbidity and mortality, medication errors have a considerable economic and societal burden.^[5,21] Thus, a number of error-prevention strategies have been proposed to increase the safety of the medication process, including pharmacists' participation in clinical rounds, having independent drug checks by many providers, and using barcode technology, medication reconciliation programs, or computerized order entry by physicians.^[7,22-24] However, proper redesigning of faulty systems should be based on an in-depth understanding of the epidemiology of medication errors.^[14] This knowledge can guide the application of error-prevention strategies and will allow more specifically targeted quality improvement efforts. Moreover, because the incidence of medication errors in a single ICU is generally low, error patterns and characteristics can more reliably be identified by reviewing data from several ICU studies.^[25] Synthesis of data on ICU medication errors will reveal most common error types, drugs associated with and factors contributing to errors, and serious error consequences, as well as provide implications for future research.

In existing studies, the incidence of medication errors is reported either per number of drug observations or per opportunities for error. Opportunities for error are difficult to define, but may properly reflect patients' exposure to risk. Differences in health care provision (such as nurse:patient ratio, personnel experience, number and types of drugs administered, and medication delivery system) among different hospitals or countries may account for the remarkable differences in incidence of medication errors among studies.^[5] Reported error incidence also depends on the exact conditions of direct observation, on the exclusion of medication errors considered to be clinically unimportant,^[14] and on the selection of medication process stages to be studied (most studies^[13,16-18] have focused on errors during drug preparation and administration).

Although definitions of medication errors may vary among studies, it is important that some error types were considerably more common than others. In remarkable agreement with findings of studies included in this review, the 3 most common medication error types in ICU studies that were based on workers' voluntary self-report^[26,27] or chart review^[28] were wrong administration time and wrong or omitted dose, whereas administration of the wrong drug or administration to the wrong patient was generally rare. In particular, the incidence of wrong-dose errors could be underestimated in voluntary selfreport studies, owing to both workers' difficulties in becoming aware of such errors and social desirability bias or self-esteem bias (because wrong-dose errors are primarily attributed to individual deficiencies, participants may tend to underreport them).^[29] Even in this case, it is important that wrong dose was among the 3 most common error types in another 2 ICU personnel self-report studies,^[25,30] thus indicating a similar trend between the direct observation and voluntary self-report methods.

Tissot et al^[16] found the wrong administration rate to be the second most common type of error, but errors related to continuous drug infusion and errors related to intermittently delivered drugs were recorded together. Recording data in this fashion renders analysis and extraction of conclusions difficult, as an incorrect continuous infusion rate means not only that the patient will receive a drug faster or slower than indicated (as in the case of wrong bolus administration rate), but that total administered dose will be inappropriate as well. Medication error types associated with continuous vs intermittent administration technique may not be comparable; therefore, these error types should be recorded separately in studies.

High number of errors associated with antibiotics, for example, may simply reflect the high number of antibiotic doses administered to ICU patients. Thus, when evaluating whether a drug (or drug category) is particularly associated with errors, more valid comparisons might be based on the incidence of errors associated with this drug (ie, the number of errors per number of observations or per opportunities for error of this drug), rather than on the absolute number of errors associated with this drug (or on the proportion of errors associated with this drug per total medication errors). In addition, more focused error prevention could be achieved through the identification of specific drugs more often associated with errors (rather than the identification of drug categories associated with errors). However, no single drug can be identified as particularly associated with errors on the basis of existing data. Consistent with findings of studies included in this review, antibiotics, sedatives/analgesics, and cardiovascular drugs (vasopressors/catecholamines) were most commonly associated with errors in a recent, self-report, multicenter ICU study.^[26] Antibiotics in particular have been identified as the highest-risk drug category in non-ICU studies and are believed to be associated with a high incidence of wrong administration time errors or omitted doses, due to variations in the interval at which antibiotics are administered.^[31,32]

Considering the multifactorial nature of medication errors, several predisposing factors have been investigated, which can be associated either with the individual (inadequate mathematical skills or medication knowledge, personal neglect, limited experience) or the system (eg, heavy workload, unfavorable working conditions, distractions, complicated orders).^[32,33] In critically ill patients, high clinical severity and high number of organ failures have also been associated with high incidences of errors.^[21,26] In agreement with findings of studies included in this review, poor communication, frequent interruptions, and workload have also been reported as the main factors contributing to errors in interview or voluntary self-report studies among ICU personnel.^[34,35] However, existing findings of direct observation studies are rather inconclusive, because none of the identified error-contributing factors was reported in more than 1 study. Moreover, possible associations between specific errorcontributing factors and specific medication error types have not been investigated to date and may be an important area for future research. For example, wrong-dose errors may be attributed to inadequate mathematical skills or drug knowledge of nurses and preparation errors by pharmacists, whereas dose omission and wrong administration time may be mainly related to system factors, such as increased workload, drug availability, pharmacy preparation timing, and time constraints with competing priorities.

According to Reason's model,^[36] most accident sequences are trapped at one or more layers of the system's defenses. In agreement with findings of studies included in this review, most ICU medication errors did not result in clinically significant consequences or patient harm in a voluntary selfreport study^[26] or in a review of safety incident reports of nursing staff.^[37] Considering that vital functions of ICU patients are continuously monitored and supported, most physiological disorders resulting from errors can be detected and properly treated at an early stage or may even require no additional treatment. For example, opioid overdose, which could cause severe respiratory depression in spontaneously breathing patients, may not considerably affect a patient receiving mechanical ventilation.^[25]

Although only a limited proportion of medication errors have life-threatening or fatal consequences, the incidence of preventable adverse drug events is not insignificant, ranging from 19 to 36.2 per 1000 ICU patient-days in US studies.^[6,38] Moreover, late consequences of medication errors could be overlooked in studies, because adverse events are generally recorded proximal to the timing of medication administration. For example, the Joint Commission has emphasized the importance of effective timing of antibiotic administration in pneumonia core measures.^[39] However, although timely antibiotic administration is important in patients with severe infections, adverse patient outcomes associated with antibiotic dose omission or wrong administration time are not recorded in most studies.^[40] Meaningful questions for future research could include whether specific medication error types or drugs are associated with a high incidence of adverse events, both early and late, and particularly with life-threatening or fatal consequences.

The small number of studies that met the inclusion criteria and the limited information about the characteristics of medication errors in some of the studies are the major limitations of this review. Another limitation is the heterogeneity of the studies, which used inconsistent definitions of errors and error incidence, were focused on different medication process stages or on different drug administration techniques, and involved different critical care settings. Additionally, although superior to other error detection methods, direct observation cannot capture errors completely. Flynn et al^[12] reported that with direct observation, 34% of true medication errors were missed and the rate of false positives (3.5%) was considerable.

Conclusion

Data derived from studies of ICU medication errors via the direct observation method suggest that the incidence of medication errors varies significantly among ICUs. Identification of the most common error types, the drugs associated with errors, the factors contributing to errors, and serious consequences of errors, is necessary to guide focused efforts to prevent medication errors. Wrong dose, dose omission, wrong administration time, and wrong administration rate (especially of continuously infused drugs) are the most common error types. The most common drug categories associated with medication errors in the ICU included antibiotics, electrolytes, cardiovascular drugs, sedatives/analgesics, and gastrointestinal drugs. Distractions, high workload, lack of drug knowledge, and poor communication may contribute to errors. Although most medication errors do not result in harm of patients, life-threatening or fatal adverse events have been reported.

Nursing personnel should design and lead future studies on their own medication errors. Research based on direct observation has yet to address many issues, mainly establishing the specific drugs most associated with medication errors and the factors contributing to medication errors in general or to specific types of medication errors. Investigation of medication error types most associated with severe adverse events is also of particular importance.

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Control estricto de la glucemia en unidades de cuidados intensivos

                                                                      Dres. Finfer S, Chittock D, Ronco J
                                                                                New England J. Med 2009;  360 (13): 1283-1297

________________________________________________________________________________ 

Introducción

La hiperglucemia es una complicación frecuente en los pacientes con enfermedades agudas, entre ellos los internados en las unidades de cuidados intensivos (UCI). Dada su relación con mayores tasas de morbilidad y mortalidad, muchas asociaciones profesionales recomiendan un control estricto de la glucemia en estos pacientes. Sin embargo, los estudios sobre los efectos de esta conducta han arrojado resultados contradictorios. Las barreras para la implementación de un control estricto comprenden el riesgo de hipoglucemia grave, las dudas acerca de la validez externa de ciertos trabajos, la dificultad para alcanzar la normoglucemia en los pacientes en estado crítico y la mayor cantidad de recursos necesarios. Los autores del presente trabajo diseñaron el estudio Normoglycemia in Intensive Care Evaluation-Survival Using Glucose Algorithm Regulation (NICE-SUGAR) para evaluar la hipótesis de que el control estricto de la glucemia reduce las tasas de mortalidad a los 90 días

Métodos

El estudio fue de grupos paralelos, aleatorizado y controlado e incluyó pacientes adultos, con enfermedades clínicas y quirúrgicas, ingresados en la UCI de 42 hospitales, y que se estimó permanecerían allí al menos por 3 días consecutivos.
Los participantes fueron asignados al azar a controles estrictos de la glucemia, con el objetivo de lograr niveles de entre 81 y 108 mg/dl (4.5 y 6 mmol/l) o convencionales, con niveles de hasta 180 mg/dl (10 mmol/l). El plantel médico conocía el plan para cada participante. La glucemia se controló mediante la infusión por bomba de insulina en solución fisiológica. La intervención se interrumpía cuando el paciente se alimentaba por vía oral o era dado de alta de la UCI, pero se reinstauraba en caso de reingresar a ésta dentro de los siguientes 90 días. La interrupción fue definitiva en caso de cumplirse los 90 días o ante la muerte del participante.
Las muestras para medir la glucemia se extrajeron, en caso de ser posible, a través de catéteres arteriales y se desaconsejaron las mediciones capilares. Los demás aspectos referidos al cuidado del paciente, incluso el nutricional, quedaron a consideración del equipo de médicos tratantes. Se determinó las características demográficas y clínicas de los participantes al ingreso, incluido el puntaje de la Acute Physiology and Chronic Health Evaluation II (APACHE II), cuyos valores van de 0 a 71 de acuerdo con la gravedad de la enfermedad, y los criterios diagnósticos de sepsis grave. Los sujetos ingresados directamente desde el quirófano o la sala de recuperación se clasificaron como quirúrgicos. Los pacientes fueron diagnosticados con diabetes (DBT) con base en sus antecedentes y como traumatizados si su ingreso a la UCI tenía lugar dentro de las 48 horas de admisión al hospital con dicho diagnóstico. Se definió la existencia de tratamiento con corticoides si su duración era de 72 horas o más inmediatamente antes del ingreso a la UCI.
Desde el inicio del estudio hasta el alta de la UCI o hasta los 90 días, lo que ocurriese primero, se registraron todas las determinaciones de glucemia; las infusiones de insulina; las trasfusiones de glóbulos rojos; los hemocultivos que resultaran positivos; el tipo y volumen de nutrición parenteral utilizada y glucosa adicional administrada; la utilización de corticoides; los puntajes del Sequential Organ Failure Assessment (SOFA), que varían entre 0 y 4 en cada órgano (cardiovascular, respiratorio, renal, hepático y hematológico), con valores más altos cuanto más grave es la disfunción orgánica, y el uso de ventilación mecánica asistida (VMA) y terapia de reemplazo renal (TRR).
El criterio de valoración primario fue la mortalidad por cualquier causa dentro de los primeros 90 días, sin ajustes estadísticos por características iniciales. Los criterios secundarios fueron la supervivencia a los 90 días, la mortalidad por causa específica, y las duraciones de la VMA, la TRR y la estadía en la UCI y en el hospital. Los criterios terciarios fueron muerte por cualquier causa dentro de los 28 días siguientes a la aleatorización, lugar de la muerte (UCI, sala de hospital u otro), incidencia de insuficiencia parenquimatosa nueva, hemocultivos positivos, recepción de transfusiones de glóbulos rojos y sus volúmenes.
El criterio primario se analizó además en 6 pares predefinidos de subgrupos: pacientes quirúrgicos y no quirúrgicos, con DBT y sin ella, traumatizados o no, con sepsis grave y sin ella, en tratamiento con corticoides o no, y con puntajes de APACHE II por debajo de 25 y de 25 o más.
La glucemia de 40 mg/dl o menos se consideró un evento adverso (EA) grave. Si la determinación era realizada con un analizador portátil, se requería su confirmación por laboratorio antes de iniciar el tratamiento.
Se determinó que una muestra de 6 100 pacientes tendría un poder estadístico del 90% para detectar una diferencia en la mortalidad entre ambos grupos de 3.8 puntos porcentuales, asumiendo una mortalidad de base del 30%. Los datos se analizaron sobre la base de la intención de tratar.

Resultados

El reclutamiento y seguimiento de los 6 104 participantes tuvo lugar entre diciembre de 2004 y noviembre de 2008. Fueron asignados a controles estrictos de glucemia (n = 3 054) o a controles convencionales (n = 3 050). A los 90 días se contaba con los datos de 3 016 y 3 014 pacientes, respectivamente. De estos 6 030 individuos, 5 275 (87.5%) fueron reclutados en Australia o Nueva Zelanda.
La media de edad de los participantes fue de 60.4 ± 17.2 años en el grupo de controles estrictos y de 59.9 ± 17.1 en el de controles convencionales; los porcentajes de hombres fueron de 62.6% y 64.2%, respectivamente. Los puntajes promedio del APACHE II fueron 21.1 ± 7.9 y 21.1 ± 8.3, y los porcentajes de ingresos quirúrgicos, de 36.9% y 37.2%. El tratamiento de la hiperglucemia se administró a 5 997 de los 6 030 pacientes (99.5%): a 2 998 de los 3 016 (99.4%) con controles estrictos y a 2 999 de los 3 014 (99.5%) con controles convencionales. La mediana de duración del tratamiento fue de 4.2 (entre 1.9 y 8.7) y de 4.3 días (entre 2 y 9), respectivamente (p = 0.69). Este se interrumpió en forma temprana en 304 (10%) de los 3 054 pacientes con controles estrictos y en 225 (7.4%) de los 3 050 con controles convencionales. Las razones fueron el pedido del paciente o su representante (26 [0.9%] y 22 [0.7%], respectivamente) o del médico tratante (115 [3.8%] y 48 [1.6%]), por EA graves (13 [0.4%] y 1 [< 0.1%]), por la decisión de cambiar a tratamiento paliativo (116 [3.8%] y 115 [3.8%]), y misceláneas (34 [1.1%] y 39 [1.3%]).
El estado vital a los 90 días no pudo establecerse en 82 de los 6 014 pacientes (1.4%), 44 en el grupo con controles estrictos y 38 en el grupo con controles convencionales. En 74 casos esto se debió al retiro o falta del consentimiento.
Los sujetos bajo controles estrictos de glucemia recibieron insulina con más frecuencia (2 931 de 3 014 [97.2%] frente a 2 080 de 3 014 [69%]; p < 0.001) y en dosis mayores (50.2 ± 38.1 UI/d frente a 16.9 ± 29; p < 0.001). El promedio de glucemia en el tiempo en el grupo con controles estrictos fue significativamente menor (115 ± 18 frente a 144 ± 23 mg/dl en el grupo con controles convencionales; p < 0.001).
El grupo con controles estrictos tenía más pacientes tratados con corticoides (1 042 de 3 010 [34.6%] frente a 955 de 3 009 [31.7%]; p = 0.02). La mediana de tiempo desde la aleatorización hasta el inicio de dicho tratamiento fue de 0 días (entre 0 y 1) en ambos grupos (p = 0.34) y su indicación más frecuente, el diagnóstico de sepsis grave (376 de 1 042 [36.1%] con controles estrictos y en 328 de 955 [34.3%] con controles convencionales; p = 0.42).
A los 90 días, 829 de los 3 010 pacientes (37.5%) con controles estrictos habían fallecido, frente a 751 de los 3 012 con controles convencionales (24.9%). La diferencia absoluta de mortalidad fue de 2.6% (intervalo de confianza [IC] 95%, 0.4-4.8) y el odds ratio (OR) para mortalidad en aquellos con controles estrictos, de 1.14 (IC 95%, 1.02-1.28; p = 0.02). La diferencia continuó siendo significativa luego de realizar ajustes estadísticos por factores de riesgo iniciales predefinidos. La mediana de supervivencia fue menor en el grupo con controles estrictos (hazard ratio, 1.11; IC 95%, 1.01-1.23; p = 0.03).
La mortalidad por causas cardiovasculares fue más frecuente en el grupo con controles estrictos (345 de 829 pacientes [41.6%] frente a 269 de 751 [35.8%] en el de controles convencionales) (diferencia absoluta de 5.8%; p = 0.02). En ambos grupos, la mayoría de las muertes ocurrieron en la UCI (546 de 829 [65.9%] y 498 de 751 [66.3%], respectivamente) o en el hospital luego de salir de la UCI (220 de 829 [26.5%] y 197 de 751 [26.2%]). Los tratamientos de soporte vital fueron evitados o detenidos en el 90% de los fallecidos.
No se describieron diferencias sustanciales entre ambos grupos en cuanto al tiempo de estadía en UCI, aparición de insuficiencia orgánica única o múltiple, días de VMA o de TRR, tasas de hemocultivos positivos o transfusiones de glóbulos rojos.

Tampoco se observaron diferencias entre los pacientes quirúrgicos y clínicos respecto de la mortalidad relacionada con el tipo de controles, ni entre aquellos con DBT y sin ella, ni entre aquellos con sepsis grave y sin ella, ni entre los que presentaban puntajes de APACHE II menores de 25 y de 25 o más. Sí se registró una tendencia hacia una mayor mortalidad en los individuos traumatizados (p = 0.07) y en los tratados con corticoesteroides (p = 0.06).
Se registraron episodios de hipoglucemia grave en 206 de 3 016 (6.8%) pacientes con controles estrictos frente a 15 de 3 014 (0.5%) con convencionales (OR, 14.7; IC 95%, 9-25.9; p < 0.001). La cantidad total de episodios fue de 272 y 16, respectivamente; con 173 (60.1%) confirmados por laboratorio, 112 (38.9%) por lecturas a la cabecera de la cama, y en 3 casos (1%) se desconoce la forma de confirmación. No hubo consecuencias a largo plazo por estos episodios.

Discusión

Los autores señalan que este estudio demuestra que los controles estrictos de glucemia en los adultos internados en UCI aumentan el riesgo absoluto de muerte a los 90 días en 2.6 puntos porcentuales; esto implica un número necesario para dañar de 38. La diferencia se mantuvo luego de realizados los ajustes por factores de confusión. También hubo más episodios de hipoglucemia grave.
La validez interna y externa se aseguró mediante el ocultamiento de los tratamientos asignados antes de la aleatorización, la selección de un resultado a largo plazo no sujeto a sesgos de selección, la evaluación de cierta cantidad de resultados clínicos importantes, el logro de un seguimiento casi completo y el cumplimiento del plan predefinido de análisis estadístico. Las glucemias difirieron significativamente entre ambos grupos de tratamiento y las tasas de hipoglucemia grave fueron menores que las mencionadas en otros trabajos. 
Los autores reconocen como limitaciones el uso de un criterio subjetivo de selección (la previsión de un tiempo determinado de estadía en la UCI), la falta de capacidad de cegamiento del  personal de salud al tratamiento administrado, y el logro de glucemias levemente por encima del rango buscado en una cantidad importante de los pacientes con controles estrictos. No se evaluaron los posibles mecanismos biológicos involucrados ni los costos de la intervención propuesta.
Respecto del análisis de los pares predefinidos de subgrupos, los autores no pueden descartar que los controles estrictos beneficien a ciertos pacientes.
Los resultados de este estudio se diferencian de los presentados en un metanálisis anterior, que no encontró variaciones en la mortalidad entre ambos tipos de controles. La diferencia podría deberse a que los participantes del grupo de control estricto de este estudio tenían glucemias menores que los del metanálisis, recibieron más insulina, presentaron más episodios de hipoglucemia y recibieron nutrición predominantemente enteral. Además, este trabajo tuvo mayor poder estadístico y un seguimiento más prolongado. En el grupo con controles estrictos hubo más pacientes tratados con corticosteroides y el exceso de mortalidad se debió  principalmente a causas cardiovasculares. Esto podría sugerir un efecto deletéreo del tratamiento con insulina sobre el sistema cardiovascular, que deberá ser investigado en futuros trabajos.
A raíz de un estudio publicado en 2001 se ha recomendado ampliamente el control estricto de la glucemia, asumiendo que dicha conducta beneficia al paciente. Los autores refieren que sus resultados indican que el logro de la normoglucemia en los pacientes en estado crítico no resulta necesariamente beneficioso y, de hecho, puede ser perjudicial, por lo que concluyen que el objetivo en los controles de glucemia debe ser mantenerla por debajo de 180 mg/dl, pero no entre 81 y 108 mg/dl, ya que dicho rango se asoció con tasas mayores de mortalidad en estos casos.

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Resumen publicado en INTRAMED - Febrero 2011

Ud. puede consultar el trabajo original en :

                                                                New England J. Med 2009;  360 (13): 1283-1297

Alterations in Acid-Base Homeostasis with Aging

                                                      Naureen Tareen, MD; Ashraf Zadshir, MD; David Martins, MD;
                                                     Glenn Nagami, MD; Barton Levine, MD; and Keith C. Norris, MD

                             J. OF THE NATIONAL MEDICAL ASSOCIATION VOL. 96, NO. 7, JULY 2004

INTRODUCTION

Acid-base disorders are commonly encountered in clinical practice and can have a  substantial impact on a patient's prognosis and outcome. The elderly are more prone to develop acid-base disturbances than the young. With age, the kidney undergoes structural and functional changes that limit the adaptive mechanisms responsible for maintaining acidbase homeostasis in response to dietary and environmental changes. In addition to a decrease in glomerular filtration rate (GFR), the capacity of the kidneys to handle electrolyte alterations and excrete an acid load is diminished with advancing age. Therefore, an improved recognition of these disorders and underlying causes will improve our ability to better manage elderly patients. In this review we have  summarized age-related changes in acid-base homeostasis that may impact clinical outcomes.

 INTRINSIC RENAL CHANGES WITH AGING

Several changes occur in glomerular number, function, and the GFR with advancing age. By the seventh decade, there is a 30-50% reduction in the number of glomeruli' and a reduction in proximal renal tubule volume and glomerular surface area.2
There is also a progressive fall in total renal plasma flow34 and the cortical component of blood flow.5 Commensurate with the decline in the number of glomeruli is an average decline in GFR of about 1% per year or 10% per decade after age 40.5,6 Despite the fall in GFR, serum creatinine levels remain unchanged in most instances due to a proportional reduction in muscle mass and endogenous creatinine production.67 The common assumption of normal kidney function on the basis of normal serum creatinine level predisposes older patients to many iatrogenic complications, including but not limited to acute renal failure, drug toxicities, and a variety of acid-base and electrolyte abnormalities.8-'0 The Cockcroft and Gault" formula has been used for many years to estimate GFR with adjustment for body weight and age. Using this formula, a serum creatinine of 1.2 mg/dl in a 20-year-old, 80-kg male reflects a GFR of 111 ml/min., while a serum creatinine of 1.2 mg/dl in a 70-year-old, 60-kg female reflects a GFR of 41 ml/min., a nearly three-fold difference.
Thus, the importance of a more accurate assessment ofGFR in an older patient cannot be overestimated.
A new formula derived from the Modification ofDiet in Renal Disease (MDRD) study has been reported to be even more accurate than Cockcroft- Gault formula in  predicting GFR as measured by 1251-iothalamate clearance'2 (see Table 1 for GFR estimation formulas; easy-to-use programs are available on websites and PDAs that need only serum creatinine level, and patient age, gender, and race).

 ACID-BASE DISORDERS

Serum [H+] is maintained within a narrow range through a series of reversible chemical buffers and physiologic pulmonary and renal responses.
Although the pH of the extracellular fluid (ECF) is maintained between 7.38-7.42 in the elderly, there is evidence to suggest this occurs at the expense of a reduced serum HCO3 reserve. A recent review noted a significant increase in the steady-state blood [H+] and a reduction in steady-state serum HCO3 from subjects aged 20-100 years, suggesting a progressive age-related, low-level metabolic acidosis."3 The homeostatic responses to chronic metabolic acidosis in aging may engender pathologic consequences, such as nephrolithiasis, bone demineralization, and muscle protein breakdown. These maladaptive changes, which may reflect subtle degrees of acidosis or the intermittent nature of the acidosis, suggest a "eubicarbonatemic" metabolic acidosis may exist in older patients and emphasizes the importance of recognition and treatment of even mild acid loads to prevent these maladaptive homeostatic  responses.'4
This eubicarbonatemic metabolic acidosis with aging appears to be most directly related to a decline of renal function and possibly an age-related, lowgrade, diet-dependent metabolic acidosis.'5 In addition to the normal physiologic changes that occur with aging, the increased frequency of comorbid conditions and/or medications which may further impact upon both pulmonary and renal function increase the susceptibilit

 APPROACH TO ACID-BASE DISORDERS

Acidosis is a process that, if left unopposed, results in acidemia (pH <7.38). Likewise, alkalosis is a process that, if left unopposed, results in alkalemia (pH >7.42). The   physiologic response to changes in pH involves changes in alveolar ventilation (pCO2), renal acid excretion and/or HCO3 reclamation.
The full respiratory response to metabolic acidosis requires hours, while the maximal renal response to respiratory disturbances usually requires three-to-four days. A rough guide to determining the appropriate physiologic response to a given primary

 METABOLIC ACIDOSIS

Metabolic acidosis is a process that results in excessive generation ofH+ or  consumption of serum HCO3. It may or may not be associated with acidemia (low plasma pH). This can occur by the addition of an acid, direct loss of bicarbonate from the gastrointestinal tract or the kidney, or rapid dilution of the ECF by a  nonbicarbonate-containing solution. The physiologic response to acidemia is an increase in ventilation that returns serum pH towards normal . In clinical practice, metabolic acidosis is divided into two functional categories- increased anion gap and normal anion gap . With high anion gap acidosis, it is important to measure the serum osmolality and compare it to the estimated osmolality (Calculated osm = 2 x plasma Na + [Glucose]/1 8 + BUN/2.8). A markedly elevated serum osmolal gap (the difference   between the actual and calculated serum osmolality) >10 mosm would indicate the presence of unaccounted osmoles, suggesting ethylene glycol or methanol as possible causes. If the osmolal gap is less than 10 mosm in the setting of a high-anion-gap acidosis, the differential diagnosis primarily consists of ketoacidosis, lactic acidosis, renal failure, salicylate ingestion, and D-lactic acidosis.
By contrast, normal anion-gap metabolic acidosis is related to a loss or reduced synthesis of bicarbonates either through the gastrointestinal tract (e.g., diarrhea) or the kidney (e.g., renal tubular acidosis), rather than generation or addition of acid (with the exception of chloride-based acid, such as HCL or arginine HCL in total parenteral nutrition supplements). A helpful step to the diagnosis of renal vs. nonrenal cause of normal anion-gap metabolic acidosis is the measurement of random urinary electrolytes and calculating the urinary anion gap, the difference between positive and negative charges (UNa+UK-UC1). An excess ofnegative charges (a negative urinary anion gap) suggests high levels of ammonium excretion. Ammonium is cation that is excreted with chloride in the urine. A negative urinary anion gap indicates an intact renal response, suggesting a nonrenal cause for the acidosis (e.g., GI bicarbonate loss with diarrhea). The absence of excess calculated negative charges indicates a renal origin to the acidosis since the kidney is not able to acidify the urine through generation of ammonium. The differential diagnosis is then narrowed to renal tubular acidosis, early stages of chronic kidney disease, use of carbonic anhydrase inhibitor, and ureteral diversion.

 METABOLIC ALKALOSIS

An increase in plasma bicarbonate concentration and an increase in blood pH   characterize metabolic alkalosis. A mixed disturbance of metabolic alkalosis and metabolic acidosis can be diagnosed by a significantly increased anion gap in the presence ofa normal or near-normal serum pH. Metabolic alkalosis can result from ECF hydrogen ion loss, the addition of bicarbonate or bicarbonate precursors to the ECF, or ECF volume contraction. Clinically, metabolic alkalosis is often divided into chloride-responsive and chloride-resistant states.  Chloride-responsive states are usually associated with volume and chloride depletion (e.g., vomiting or nasogastric suction) and characterized by a low urinary chloride concentration, <10 mEq/L. One exception is the active use of diuretics in which instance urine chloride concentration may be >lOmEq/L. The elderly are more highly predisposed to developing volume depletion. 21,22 Milk alkali syndrome and diuretic use should always be considered in an older patient with metabolic alkalosis. By contrast, chloride-resistant metabolic alkalosis is usually due to a high aldosterone or aldosterone-like state, such as primary hyperaldosteronism or Cushing's syndrome, and associated with an increase in sodium retention, hypertension and a high urinary chloride concentration.

 RESPIRATORY ACIDOSIS

Respiratory acidosis is characterized by an increase in PCO2 and a reduction in pH. The increased PCO2 results in an increased carbonic acid concentration. In respiratory acidosis, carbonic acid is buffered by intracellular buffers, including hemoglobin and phosphate, resulting in a small increase in plasma bicarbonate concentration. The kidneys compensate by increasing acid secretion and replenishing the bicarbonate pool. This renal response may take three-to-four hours to fully develop. Conditions, such as pulmonary obstruction, stroke, primary depression ofthe respiratory center, mechanical/structural defect, or a neuromuscular disorder, can lead to a reduction in alveolar ventilation with PCO2 retention and acidemia. Salicylate intoxication which classically presents as a mixed metabolic acidosis and respiratory alkalosis may present as a respiratory acidosis in the elderly due to the frequent association of other ingested substances, primarily central nervous system depressants.'8"19

 RESPIRATORY ALKALOSIS

Respiratory alkalosis is a common acid-base disorder disorder encountered in the elderly. It results from increased alveolar ventilation leading to a reduced PCO2 and an elevated plasma pH. The initial response to alkalemia is buffering with intracellular protons. Renal compensation occurs over several days with a reduction in both net acid excretion and bicarbonate reclamation, reducing plasma bicarbonate concentration and lowering plasma pH towards normal. Clinical disorders which increase the central nervous system respiratory drive or stimulate chemoreceptors may lead to hyperventilation and reduce systemic PCO2. In the elderly, it is especially important to consider anxiety and associated hyperventilation, central nervous system infection/infarction, sepsis, pulmonary edema, pulmonary emboli and/or medications/drugs-especially salicylate intoxication.'

 CONCLUSION

In summary, the elderly-particularly acutely ill elderly-are at a greater risk for the development of marked derangements in systemic acid-base homeostasis that may delay recovery, prolong hospitalizations, and adversely affect clinical outcomes. There is unequivocal evidence that more severe acid-base disorders are associated with a greater risk for mortality.  A greater understanding ofthe changes in renal physiology and related neurohormonal responses that occur with aging can help guide the clinician toward a more timely and appropriate response to a given disease process.

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Estas son partes del trabajo que Ud puede consultar para leer completo en:

J. OF THE NATIONAL MEDICAL ASSOCIATION VOL. 96, NO. 7, JULY 2004

A1C Versus Glucose Testing: A Comparison: Perspective

                                                    David B. Sacks,         
                                                                              Diabetes Care. 2011;34(2)

Introduction

Diabetes was originally identified by the presence of glucose in the urine. Almost 2,500 years ago it was noticed that ants were attracted to the urine of some individuals. In the 18th and 19th centuries the sweet taste of urine was used for diagnosis before chemical methods became available to detect sugars in the urine. Tests to measure glucose in the blood were developed over 100 years ago, and hyperglycemia subsequently became the sole criterion recommended for the diagnosis of diabetes. Initial diagnostic criteria relied on the response to an oral glucose challenge, while later measurement of blood glucose in an individual who was fasting also became acceptable. The most widely accepted glucose-based criteria for diagnosis are fasting plasma glucose (FPG) ≥126 mg/dL or a 2-h plasma glucose ≥200 mg/dL during an oral glucose tolerance test (OGTT) on more than one occasion.^[1,2] In a patient with classic symptoms of diabetes, a single random plasma glucose ≥200 mg/dL is considered diagnostic.^[1] Before 2010 virtually all diabetes societies recommended blood glucose analysis as the exclusive method to diagnose diabetes. Notwithstanding these guidelines, over the last few years many physicians have been using hemoglobin A1C to screen for and diagnose diabetes.^[3] Although considered the "gold standard" for diagnosis, measurement of glucose in the blood is subject to several limitations, many of which are not widely appreciated. Measurement of A1C for diagnosis is appealing but has some inherent limitations. These issues have become the focus of considerable attention with the recent publication of the Report of the International Expert Committee that recommended the use of A1C for diagnosis of diabetes,^[4] a position that has been endorsed (at the time of writing) by the American Diabetes Association (ADA),^[1] the Endocrine Society, and in a more limited fashion by American Association of Clinical Endocrinologists/American College of Endocrinology.^[5] This review will provide an overview of the factors that influence glucose and A1C testing.

Factors Contributing to Variation in Results

Before addressing glucose and A1C, it is important to consider the factors that impact the results of any blood test. While laboratory medicine journals have devoted some discussion to the sources of variability in results of blood tests, this topic has received little attention in the clinical literature. Factors that contribute to variation can conveniently be divided into three categories, namely biological, preanalytical, and analytical. Biological variation comprises both differences within a single person (termed intraindividual) and between two or more people (termed interindividual). Preanalytical issues pertain to the specimen before it is measured. Analytical differences result from the measurement procedure itself. The influence of these factors on both glucose and A1C results will be addressed in more detail below.

Glucose Measurement

FPG

Measurement of glucose in plasma of fasting subjects is widely accepted as a diagnostic criterion for diabetes.^[1,2] Advantages include inexpensive assays on automated instruments that are available in most laboratories worldwide  Nevertheless, FPG is subject to some limitations. One report that analyzed repeated measurements from 685 fasting participants without diagnosed diabetes from the Third National Health and Nutrition Examination Survey (NHANES III) revealed that only 70.4% of people with FPG ≥126 mg/dL on the first test had FPG ≥126 mg/dL when analysis was repeated ~2 weeks later.^[6] Numerous factors may contribute to this lack of reproducibility. These are elaborated below.

Biological Variation. Fasting glucose concentrations vary considerably both in a single person from day to day and also between different subjects. Intraindividual variation in a healthy person is reported to be 5.7-8.3%, whereas interindividual variation of up to 12.5% has been observed.^[6,7] Based on a CV (coefficient of variation) of 5.7%, FPG can range from 112-140 mg/dL in an individual with an FPG of 126 mg/dL. (It is important to realize that these values encompass the 95% confidence interval, and 5% of values will be outside this range.)

Preanalytical Variation. Numerous factors that occur before a sample is measured can influence results of blood tests. Examples include medications, venous stasis, posture, and sample handling. The concentration of glucose in the blood can be altered by food ingestion, prolonged fasting, or exercise.^[8] It is also important that measurements are performed in subjects in the absence of intercurrent illness, which frequently produces transient hyperglycemia.^[9] Similarly, acute stress (e.g., not being able to find parking or having to wait) can alter blood glucose concentrations.

Samples for fasting glucose analysis should be drawn after an overnight fast (no caloric ingestion for at least 8 h), during which time the subject may consume water ad lib.^[10] The requirement that the subject be fasting is a considerable practical problem as patients are usually not fasting when they visit the doctor, and it is often inconvenient to return for phlebotomy. For example, at an HMO affiliated with an academic medical center, 69% (5,752 of 8,286) of eligible participants were screened for diabetes.^[11] However, FPG was performed on only 3% (152) of these individuals. Ninety-five percent (5,452) of participants were screened by random plasma glucose measurements, a technique not consistent with ADA recommendations. In addition, blood drawn in the morning as FPG has a diurnal variation. Analysis of 12,882 participants aged 20 years or older in NHANES III who had no previously diagnosed diabetes revealed that mean FPG in the morning was considerably higher than in the afternoon.^[12] Prevalence of diabetes (FPG ≥126 mg/dL) in afternoon-examined patients was half that of participants examined in the morning. Other patient-related factors that can influence the results include food ingestion when supposed to be fasting and hypocaloric diet for a week or more prior to testing.

Glucose concentrations decrease in the test tube by 5-7% per hour due to glycolysis.^[13] Therefore, a sample with a true blood glucose value of 126 mg/dL would have a glucose concentration of ~110 mg/dL after 2 h at room temperature. Samples with increased concentrations of erythrocytes, white blood cells, or platelets have even greater rates of glycolysis. A common misconception is that sodium fluoride, an inhibitor of glycolysis, prevents glucose consumption. While fluoride does attenuate in vitro glycolysis, it has no effect on the rate of decline in glucose concentrations in the first 1 to 2 h after blood is collected, and glycolysis continues for up to 4 h in samples containing fluoride.^[14] The delay in the glucose stabilizing effect of fluoride is most likely the result of glucose metabolism proximal to the fluoride target enolase.^[15] After 4 h, fluoride maintains a stable glucose concentration for 72 h at room temperature.^[14] A recent publication showed that acidification of the blood sample inhibits glycolysis in the first 2 h after phlebotomy,^[16] but the collection tubes used in that study are not commercially available. Placing tubes in ice water immediately after collection may be the best method to stabilize glucose initially,^[2,16] but this is not a practical solution in most clinical situations. Separating cells from plasma within minutes is also effective, but impractical.

The nature of the specimen analyzed can have a large influence on the glucose concentration. Glucose can be measured in whole blood, serum, or plasma, but plasma is recommended by both the ADA and World Health Organization (WHO) for diagnosis.^[1,2] However, many laboratories measure glucose in serum, and these values may differ from those in plasma. There is a lack of consensus in the published literature, with glucose concentrations in plasma reported to be lower than,^[17] higher than,^[16,18,19] or the same as^[20] those in serum. Importantly, glucose concentrations in whole blood are 11% lower than those in plasma because erythrocytes have a lower water content than plasma.^[13] The magnitude of the difference in glucose between whole blood and plasma changes with hematocrit. Most devices (usually handheld meters) that measure glucose in capillary blood use whole blood. While the majority of these report a plasma equivalent glucose value,^[21] this result is not accurate in patients with anemia^[22] (unless the meter measures hematocrit).

The source of the blood is another variable. Although not a substantial problem in the fasting state, capillary glucose concentrations can be 20-25% higher (mean of 30 mg/dL) than venous glucose during an OGTT.^[23] This finding has practical implications for the OGTT, particularly because the WHO deems capillary blood samples acceptable for the diagnosis of diabetes.^[2]

Analytical Variation. Glucose is measured in central laboratories almost exclusively using enzymatic methods, predominantly with glucose oxidase or hexokinase.^[24] The following terms are important for understanding measurement: accuracy indicates how close a single measurement is to the "true value" and precision (or repeatability) refers to the closeness of agreement of repeated measurements under the same conditions. Precision is usually expressed as CV; methods with low CV have high precision. Numerous improvements in glucose measurement have produced low within-laboratory imprecision (CV <2.5%). Thus, the analytical variability is considerably less than the biological variability, which is up to 8.3%. Nevertheless, accuracy of measurement remains a problem. There is no program to standardize results among different instruments and different laboratories. Bias (deviation of the result from the true value) and variation among different lots of calibrators can reduce the accuracy of glucose results. (A calibrator is a material of known concentration that is used to adjust a measurement procedure.) A comparison of serum glucose measurements (target value 98.5 mg/dL) was performed among ~6,000 laboratories using 32 different instruments.^[25] Analysis revealed statistically significant differences in bias among clinical laboratory instruments, with biases ranging from -6 to +7 mg/dL (-6 to +7%) at a glucose concentration of 100 mg/dL. These considerable differences among laboratories can result in the potential misclassification of >12% of patients.^[4] Similarly, inspection of a College of American Pathologists (CAP) survey comprising >5,000 laboratories revealed that one-third of the time the results among instruments for an individual measurement could range between 141 and 162 mg/dL.^[26] This variation of 6.9% above or below the mean reveals that one-third of the time the glucose results on a single patient sample measured in two different laboratories could differ by 14%.

OGTT

The OGTT evaluates the efficiency of the body to metabolize glucose and for many years has been used as the "gold standard" for diagnosis of diabetes. An increase in postprandial glucose concentration usually occurs before fasting glucose increases. Therefore, postprandial glucose is a sensitive indicator of the risk for developing diabetes and an early marker of impaired glucose homeostasis  Published evidence suggests that an increased 2-h plasma glucose during an OGTT is a better predictor of both all-cause mortality and cardiovascular mortality or morbidity than the FPG.^[27,28] The OGTT is accepted as a diagnostic modality by the ADA, WHO/International Diabetes Federation (IDF),^[1,2] and other organizations. However, extensive patient preparation is necessary to perform an OGTT. Important conditions include, among others, ingestion of at least 150 g of dietary carbohydrate per day for 3 days prior to the test, a 10- to 16-h fast, and commencement of the test between 7:00 A.M. and 9:00 A.M..^[24] In addition, numerous conditions other than diabetes can influence the OGTT.^[24] Consistent with this, published evidence reveals a high degree of intraindividual variability in the OGTT, with a CV of 16.7%, which is considerably greater than the variability for FPG.^[6] These factors result in poor reproducibility of the OGTT, which has been documented in multiple studies.^[29,30] The lack of reproducibility, inconvenience, and cost of the OGTT led the ADA to recommend that FPG should be the preferred glucose-based diagnostic test.^[1] Note that glucose measurement in the OGTT is also subject to all the limitations described for FPG.

A1C Measurement

A1C is formed by the nonenzymatic attachment of glucose to the N-terminal valine of the β-chain of hemoglobin.^[24] The life span of erythrocytes is ~120 days, and consequently A1C reflects long-term glycemic exposure, representing the average glucose concentration over the preceding 8-12 weeks.^[31,32] Both observational studies^[33] and controlled clinical trials^[34,35] demonstrate strong correlation between A1C and retinopathy, as well as other microvascular complications of diabetes. More importantly, the A1C value predicts the risk of microvascular complications and lowering A1C concentrations (by tight glycemic control) significantly reduces the rate of progression of microvascular complications.^[34,35]

Biological Variation. Intraindividual variation of A1C in nondiabetic people is minimal^[36], with CV <1%.^[37] Variability between individuals is greater. Data derived from several investigators imply that A1C values may not be constant among all individuals despite the presence of similar blood glucose or fructosamine concentrations.^[38] Some investigators have termed this a "glycation gap" and proposed that there are differences in the rate of glycation of hemoglobin ("low and high glycators").^[39] Studies of twins with type 1 diabetes support a genetic contribution to A1C values,^[40] and heritability of the glycation gap was observed in healthy female twins.^[41] However, the glycation gap is essentially a measure of A1C adjusted for fructosamine. Importantly, measurement of fructosamine, which is glycated albumin and protein, suffers from several limitations.^[42] In addition, some authors have questioned the statistical analysis (which is not standard) used in determining the glycation gap and noted the statistical tautology that the outcome is correlated with the residual from a regression.^[43] Importantly, the postulate of a glycation gap remains unsubstantiated by data because glycation rates cannot be measured accurately in vivo. In addition, the hemoglobin glycation index (difference between observed A1C and that predicted from blood glucose) is not an independent predictor of the risk of microvascular complications,^[43] and the possible clinical significance of the glycation gap is unclear.

Accumulating evidence supports the hypothesis that race influences A1C. Initial studies in patients with diabetes reported statistically significant differences in A1C concentrations among races.^[44] While adjusted for factors that may influence glycemia, it remains possible that these differences may be due to variations in glycemic control. More compelling support was provided in NHANES III where Mexican Americans and blacks had higher average A1C values than whites.^[45,46] Similar findings were observed in adults with impaired glucose tolerance in the Diabetes Prevention Program^[47] and validated in a cross-sectional analysis of two studies.^[48] Collectively these data suggest that there are differences in A1C concentrations among racial groups. However, it is not clear that these changes have clinical significance. A1C was measured in the Atherosclerosis Risk in Communities (ARIC) study in 11,092 adults who did not have a history of diabetes or cardiovascular disease.^[49] Consistent with prior publications, blacks had mean A1C values 0.4% higher than whites. Nevertheless, race did not modify the association between the A1C value and adverse cardiovascular outcomes and death.^[49] Because follow-up revealed that blacks with biochemically defined incident diabetes were significantly less likely than whites to report having received a diagnosis of diabetes by a physician, the authors speculate that delays in diagnosis may explain the higher A1C values in blacks.

The molecular mechanism underlying the racial and ethnic differences remains to be established. Possibilities include differences in rates of glucose uptake into erythrocytes, rates of intraerythrocytic glucose metabolism, rates of glucose attachment to or release from hemoglobin or erythrocyte life span.^[50,51] Regardless of the mechanism, the variations in A1C concentrations are relatively small (≤0.4%), and no consensus has been reached on whether different cutoffs should be used for different races.

Preanalytical Variation. Most factors that alter FPG do not significantly affect A1C concentrations. Acute illness, short-term lifestyle changes (e.g., exercise), recent food ingestion, and sample handling do not significantly alter A1C values  Importantly, whole blood samples are stable for 1 week at 4°C and for at least 1 year at -70°C or colder.^[13,52]

The interpretation of A1C depends on the erythrocytes having a normal life span. Patients with hemolytic disease or other conditions with shortened erythrocyte survival have a substantial reduction in A1C.^[53] Similarly, individuals with acute blood loss have spuriously low A1C values because of an increased fraction of young erythrocytes. False increases in A1C have been reported with some methods in patients with hypertriglyceridemia, hyperbilirubinemia, uremia, chronic alcoholism, or chronic ingestion of salicylates.^[13] Because most interferences are method specific, in many cases they can be overcome by selecting an appropriate method that is not subject to the interference.

Individuals with iron deficiency anemia have increased A1C and fructosamine concentrations,^[54] both of which are reduced by therapy with iron.^[54,55] A mechanism for the higher A1C was recently identified by the demonstration that malondialdehyde, which is increased in subjects with iron deficiency anemia,^[54] augments glycation of hemoglobin.^[56] However, the magnitude of the increase in A1C is probably small. Examination of 10,535 adults without self-reported diabetes in NHANES III revealed that while 13.7% of women had iron deficiency, only 4.74% and 0.48% had A1C ≥5.5% or ≥6.5%, respectively.^[57] Iron deficiency in women was associated with a small (odds ratio 1.39) yet significant greater odds of A1C ≥5.5% but not with greater odds of A1C ≥6.5%. Iron deficiency was rare in men (<0.5%).^[57] Nevertheless, it would seem prudent to correct the iron deficiency before measuring A1C in individuals with severe iron deficiency anemia.

Analytical Variation. There are ~100 different methods used to measure A1C. The most widely used commercial methods use either antibodies (immunoassays) or cation-exchange chromatography (most commonly high-performance liquid chromatography) to separate the glycated (A1C) from the nonglycated hemoglobin.^[24] The National Glycohemoglobin Standardization Program (NGSP) has been instrumental in standardizing A1C testing among laboratories,^[58,59] particularly (but not exclusively) in the U.S. The NGSP has markedly improved the performance of A1C testing.^[58] At the time of writing, the vast majority (93%) of clinical laboratories that participate in CAP surveys use methods with between-laboratory CVs <5% (www.ngsp.org). Within laboratory CVs for some methods are as low as <0.5%. In addition, the International Federation for Clinical Chemistry (IFCC) developed a reference method using mass spectrometry (or capillary electrophoresis) for A1C measurement, which should result in international harmonization as it facilitates traceability to a metrologically sound accuracy base. It is important to emphasize that the IFCC method is technically complex, time consuming, and expensive and is not designed for routine analysis of patient samples.

Hemoglobin variants affect some A1C measurements. The most common variants are HbS, HbE, HbC, and HbD. A1C measurement is not appropriate in subjects homozygous for HbS or HbC, with HbSC or with any other variant that alters erythrocyte survival. However, A1C can be measured accurately in individuals heterozygous for HbS, HbE, HbC, or HbD and in those with increased HbF, provided an appropriate assay is used.^[53,60] Only ~4% of the 3,378 clinical laboratories that participated in the 2010 GH2 College of American Pathologists survey (which measures A1C) use methods in which HbAS or HbAC has clinically significant interference. In addition, if the sample is analyzed by high-performance liquid chromatography method, careful inspection of the chromatogram usually reveals the aberrant peaks produced by the variant hemoglobin. The presence of a hemoglobin variant should be considered if A1C is >15% or if a large change in A1C coincides with a change in laboratory A1C method.^[53] In these situations, hemoglobin electrophoresis should be performed. It is important to emphasize that, like any other test, A1C results that are inconsistent with the clinical presentation

Perspective

Notwithstanding the use of glucose (FPG and/or the OGTT) as the "gold standard" for the diagnosis of diabetes for many years, glucose testing suffers from several deficiencies. The requirement that the subject be fasting at the time the blood is drawn is a considerable inconvenience. While our ability to measure glucose has improved, inherent biological variability can produce very large differences within and among individuals. In conjunction with lack of sample stability, which is difficult to overcome in clinical practice, these factors results in lack of reproducibility of glucose testing.

A1C, which reflects chronic blood glucose values, is routinely used in monitoring glycemic control and guiding therapy. The significant reduction in microvascular complications with lower A1C and the absence of sample lability, combined with several other advantages, have led to the recommendation by some organizations that A1C be used for screening and diagnosis of diabetes.^[1] Accumulating evidence suggests that racial differences in A1C values may be present, and the possible clinical significance of this needs to be determined. Importantly, A1C cannot be measured in certain conditions. Despite these caveats, A1C can be measured accurately in the vast majority of people. A comprehension of the factors that influence A1C values and the conditions where it should not be used will produce accurate and clinically meaningful results. The convenience of sampling at any time without regard to food ingestion makes it likely that measurement of A1C will result in the detection of many of the millions of people with diabetes who are currently undiagnosed.

References

• 1. American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care 2010;33(Suppl. 1):S62-S69
• 2. World Health Organization. Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycermia: Report of a WHO/IDF Consultation. Geneva, World Health Organization, 2006
• 3. Saudek CD, Herman WH, Sacks DB, Bergenstal RM, Edelman D, Davidson MB. A new look at screening and diagnosing diabetes mellitus. J Clin Endocrinol Metab 2008;93:2447-2453
• 4. International Expert Committee. International Expert Committee report on the role of the A1C assay in the diagnosis of diabetes. Diabetes Care 2009;32:1327-1334
• 5. American Association of Clinical Endocrinologists Board of Directors; American College of Endocrinologists Board of Trustees. American Association of Clinical Endocrinologists/American College of Endocrinology statement on the use of hemoglobin A1c for the diagnosis of diabetes. Endocr Pract 2010;16:155-156
• 6. Selvin E, Crainiceanu CM, Brancati FL, Coresh J. Short-term variability in measures of glycemia and implications for the classification of diabetes. Arch Intern Med 2007;167:1545-1551
• 7. Lacher DA, Hughes JP, Carroll MD. Estimate of biological variation of laboratory analytes based on the Third National Health and Nutrition Examination Survey. Clin Chem 2005;51:450-452
• 8. Burtis CA, Ashwood ER, Bruns DE Young DS, Bermes EW. Preanalytical variables and biological variations. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, Eds. St. Louis, Elsevier Saunders, 2006, p. 449-473
• 9. Dungan KM, Braithwaite SS, Preiser JC. Stress hyperglycaemia. Lancet 2009;373:1798-1807
• 10. American Diabetes Association. Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes Care 1997;20:1183-1197
• 11. Ealovega MW, Tabaei BP, Brandle M, Burke R, Herman WH. Opportunistic screening for diabetes in routine clinical practice. Diabetes Care 2004;27:9-12
• 12. Troisi RJ, Cowie CC, Harris MI. Diurnal variation in fasting plasma glucose: implications for diagnosis of diabetes in patients examined in the afternoon. JAMA 2000;284:3157-3159
• 13. Sacks DB, Bruns DE, Goldstein DE, Maclaren NK, McDonald JM, Parrott M. Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clin Chem 2002;48:436-472
• 14. Chan AY, Swaminathan R, Cockram CS. Effectiveness of sodium fluoride as a preservative of glucose in blood. Clin Chem 1989;35:315-317
• 15. Bruns DE, Knowler WC. Stabilization of glucose in blood samples: why it matters. Clin Chem 2009;55:850-852
• 16. Gambino R, Piscitelli J, Ackattupathil TA, et al. Acidification of blood is superior to sodium fluoride alone as an inhibitor of glycolysis. Clin Chem 2009;55:1019-1021
• 17. Ladenson JH, Tsai LM, Michael JM, Kessler G, Joist JH. Serum versus heparinized plasma for eighteen common chemistry tests: is serum the appropriate specimen? Am J Clin Pathol 1974;62:545-552
• 18. Stahl M, Jørgensen LG, Hyltoft Petersen P, Brandslund I, de Fine Olivarius N, Borch-Johnsen K. Optimization of preanalytical conditions and analysis of plasma glucose. 1. Impact of the new WHO and ADA recommendations on diagnosis of diabetes mellitus. Scand J Clin Lab Invest 2001;61:169-179
• 19. Carstensen B, Lindström J, Sundvall J, Borch-Johnsen K, Tuomilehto J; DPS Study Group Measurement of blood glucose: comparison between different types of specimens. Ann Clin Biochem 2008;45:140-148
• 20. Miles RR, Roberts RF, Putnam AR, Roberts WL. Comparison of serum and heparinized plasma samples for measurement of chemistry analytes. Clin Chem 2004;50:1704-1706
• 21. Steffes MW, Sacks DB. Measurement of circulating glucose concentrations: the time is now for consistency among methods and types of samples. Clin Chem 2005;51:1569-1570
• 22. Tang Z, Lee JH, Louie RF, Kost GJ. Effects of different hematocrit levels on glucose measurements with handheld meters for point-of-care testing. Arch Pathol Lab Med 2000;124:1135-1140
• 23. Larsson-Cohn U. Differences between capillary and venous blood glucose during oral glucose tolerance tests. Scand J Clin Lab Invest 1976;36:805-808
• 24. Burtis CA, Ashwood ER, Bruns DE Sacks DB. Carbohydrates. In Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, Eds. St. Louis, Elsevier Saunders, 2006, p. 837-902
• 25. Miller WG, Myers GL, Ashwood ER, et al. State of the art in trueness and interlaboratory harmonization for 10 analytes in general clinical chemistry. Arch Pathol Lab Med 2008;132:838-846
• 26. Gambino R. Glucose: a simple molecule that is not simple to quantify. Clin Chem 2007;53:2040-2041
• 27. de Vegt F, Dekker JM, Ruhé HG, et al. Hyperglycaemia is associated with all-cause and cardiovascular mortality in the Hoorn population: the Hoorn Study. Diabetologia 1999;42:926-931
• 28. DECODE Study Group. Glucose tolerance and mortality: comparison of WHO and American Diabetes Association diagnostic criteria. The DECODE study group. European Diabetes Epidemiology Group. Diabetes epidemiology: collaborative analysis of diagnostic criteria in Europe. Lancet 1999;354:617-621 [see comments]
• 29. Mooy JM, Grootenhuis PA, de Vries H, et al. Intra-individual variation of glucose, specific insulin and proinsulin concentrations measured by two oral glucose tolerance tests in a general Caucasian population: the Hoorn Study. Diabetologia 1996;39:298-305
• 30. Brohall G, Behre CJ, Hulthe J, Wikstrand J, Fagerberg B. Prevalence of diabetes and impaired glucose tolerance in 64-year-old Swedish women: experiences of using repeated oral glucose tolerance tests. Diabetes Care 2006;29:363-367
• 31. Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose Study Group. Translating the A1C assay into estimated average glucose values. Diabetes Care 2008;31:1473-1478
• 32. Goldstein DE, Little RR, Lorenz RA, et al. Tests of glycemia in diabetes. Diabetes Care 2004;27:1761-1773
• 33. Sabanayagam C, Liew G, Tai ES, et al. Relationship between glycated haemoglobin and microvascular complications: is there a natural cut-off point for the diagnosis of diabetes? Diabetologia 2009;52:1279-1289
• 34. The Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med 1993;329:977-986
• 35. UK Prospective Diabetes Study (UKPDS) Group. Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet 1998;352:837-853
• 36. Kilpatrick ES, Maylor PW, Keevil BG. Biological variation of glycated hemoglobin: implications for diabetes screening and monitoring. Diabetes Care 1998;21:261-264
• 37. Rohlfing C, Wiedmeyer HM, Little R, et al. Biological variation of glycohemoglobin. Clin Chem 2002;48:1116-1118
• 38. Cohen RM, Smith EP. Frequency of HbA1c discordance in estimating blood glucose control. Curr Opin Clin Nutr Metab Care 2008;11:512-517
• 39. Hempe JM, Gomez R, McCarter RJ Jr., Chalew SA. High and low hemoglobin glycation phenotypes in type 1 diabetes: a challenge for interpretation of glycemic control. J Diabetes Complications 2002;16:313-320
• 40. Snieder H, Sawtell PA, Ross L, Walker J, Spector TD, Leslie RD. HbA(1c) levels are genetically determined even in type 1 diabetes: evidence from healthy and diabetic twins. Diabetes 2001;50:2858-2863
• 41. Cohen RM, Snieder H, Lindsell CJ, et al. Evidence for independent heritability of the glycation gap (glycosylation gap) fraction of HbA1c in nondiabetic twins. Diabetes Care 2006;29:1739-1743
• 42. Windeler J, Köbberling J. The fructosamine assay in diagnosis and control of diabetes mellitus scientific evidence for its clinical usefulness? J Clin Chem Clin Biochem 1990;28:129-138
• 43. Lachin JM, Genuth S, Nathan DM, Rutledge BN. The hemoglobin glycation index is not an independent predictor of the risk of microvascular complications in the Diabetes Control and Complications Trial. Diabetes 2007;56:1913-1921
• 44. Wisdom K, Fryzek JP, Havstad SL, Anderson RM, Dreiling MC, Tilley BC. Comparison of laboratory test frequency and test results between African-Americans and Caucasians with diabetes: opportunity for improvement. Findings from a large urban health maintenance organization. Diabetes Care 1997;20:971-977
• 45. Saaddine JB, Fagot-Campagna A, Rolka D, et al. Distribution of HbA(1c) levels for children and young adults in the U.S.: Third National Health and Nutrition Examination Survey. Diabetes Care 2002;25:1326-1330
• 46. Davidson MB, Schriger DL. Effect of age and race/ethnicity on HbA1c levels in people without known diabetes mellitus: implications for the diagnosis of diabetes. Diabetes Res Clin Pract 2010;87:415-421
• 47. Herman WH, Ma Y, Uwaifo G, et al.; Diabetes Prevention Program Research Group. Differences in A1C by race and ethnicity among patients with impaired glucose tolerance in the Diabetes Prevention Program. Diabetes Care 2007;30:2453-2457
• 48. Ziemer DC, Kolm P, Weintraub WS, et al. Glucose-independent, black-white differences in hemoglobin A1c levels: a cross-sectional analysis of 2 studies. Ann Intern Med 2010;152:770-777
• 49. Selvin E, Steffes MW, Zhu H, et al. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. N Engl J Med 2010;362:800-811
• 50. Herman WH, Cohen RM. Hemoglobin A1c: teaching a new dog old tricks. Ann Intern Med 2010;152:815-817
• 51. Cohen RM, Franco RS, Khera PK, et al. Red cell life span heterogeneity in hematologically normal people is sufficient to alter HbA1c. Blood 2008;112:4284-4291
• 52. Little RR, Rohlfing CL, Tennill AL, Connolly S, Hanson S. Effects of sample storage conditions on glycated hemoglobin measurement: evaluation of five different high performance liquid chromatography methods. Diabetes Technol Ther 2007;9:36-42
• 53. Bry L, Chen PC, Sacks DB. Effects of hemoglobin variants and chemically modified derivatives on assays for glycohemoglobin. Clin Chem 2001;47:153-163 [Review]
• 54. Sundaram RC, Selvaraj N, Vijayan G, Bobby Z, Hamide A, Rattina Dasse N. Increased plasma malondialdehyde and fructosamine in iron deficiency anemia: effect of treatment. Biomed Pharmacother 2007;61:682-685
• 55. Tarim O, Küçükerdoğan A, Günay U, Eralp O, Ercan I. Effects of iron deficiency anemia on hemoglobin A1c in type 1 diabetes mellitus. Pediatr Int 1999;41:357-362
• 56. Selvaraj N, Bobby Z, Sathiyapriya V. Effect of lipid peroxides and antioxidants on glycation of hemoglobin: an in vitro study on human erythrocytes. Clin Chim Acta 2006;366:190-195
• 57. Kim C, Bullard KM, Herman WH, Beckles GL. Association between iron deficiency and A1C Levels among adults without diabetes in the National Health and Nutrition Examination Survey, 1999-2006. Diabetes Care 2010;33:780-785
• 58. Little RR, Rohlfing CL, Wiedmeyer HM, Myers GL, Sacks DB, Goldstein DE; NGSP Steering Committee. The national glycohemoglobin standardization program: a five-year progress report. Clin Chem 2001;47:1985-1992
• 59. Berg AH, Sacks DB. Haemoglobin A1c analysis in the management of patients with diabetes: from chaos to harmony. J Clin Pathol 2008;61:983-987
• 60. Little RR, Sacks DB. HbA1c: how do we measure it and what does it mean? Curr Opin Endocrinol Diabetes Obes 2009;16:113-118

Do You Report an Accurate International Normalized Ratio?

                                                                       Richard A. Marlar, PhD; Jana N. Gausman
                                                                       Laboratory Medicine. 2011;42(3):176-181.

Abstract

The current method for monitoring vitamin K antagonist (AVK) anticoagulant therapy is the international normalized ratio (INR) that provides consistency and standardization for the prothrombin time (PT) assay value. Even after the standardization of the INR, inaccuracies of this value have still been reported. To make the INR even more accurate, better local assessments of INR parameters are becoming available. These new methods use plasmas with certified INR values to locally verify and, if necessary, recalculate the international sensitivity index (ISI) for the local laboratory's reagent and instrument system. This CE Update will discuss the concepts of local verification and calibration to better define the manufacturer's assigned ISI value, thus reporting more accurate INR results.

Introduction

Our understanding of the basic science and clinical issues surrounding hemostasis has skyrocketed within the last 10 to 15 years. These advances have: 1) established better treatment for patients at risk for hemorrhage or thrombosis; 2) identified new hereditary coagulation disorders; and 3) provided mechanism(s) for clinical hemostatic diseases. With this in mind, clinicians have begun to put more demand on the coagulation laboratory. The laboratory has had to keep pace by developing new coagulation tests and better standardizing those tests already in use. The cornerstones of clinical coagulation testing are the prothrombin time and/or international normalized ratio (PT/INR) and the activated partial thromboplastin time (aPTT) for identifying and monitoring clinical coagulation disorders and therapeutics. Manufacturers have varied the sensitivities of these reagents to more easily assess this variety of clinical conditions. It now has become important for each laboratory to evaluate the commercial reagents to determine the most appropriate one for their clinical needs. The criteria for how reagents should be evaluated include: sensitivity for intended use, compatibility with instrumentation, number of assays performed each day, and cost.
In this CE Update, we discuss: 1) how to determine the INR; 2) how to locally verify and calibrate the PT reagent for more accurate INR values; and 3) the clinical use of the INR for monitoring anti-vitamin K anticoagulant therapy.

 Oral Anticoagulant Therapy Monitoring Using the PT/INR

Anticoagulant therapy is used to treat and/or prevent both arterial and venous thrombosis.^[1] Currently in the United States, IV anticoagulants (heparin and direct thrombin inhibitors [DTI]) are administered to inhibit further clot formation. The oral drug Coumadin (or warfarin) is given for long-term prevention of new thrombus formation; however, it is an indirect acting drug requiring 3 to 5 days to reach therapeutic effectiveness.^[1] Warfarin derivatives are the standard therapy worldwide.^[3] Annually, there are more than 21 million prescriptions written in the United States.^[3] Warfarin derivatives (generally known as vitamin K antagonists [AVK]) act by inhibiting the vitamin K-associated post-translational modifications of the vitamin K-dependent clotting factors.^[1] Unfortunately, warfarin has a very narrow therapeutic window and dosing responses vary between individuals of up to 10-fold and 2-3 fold within an individual caused by changes in medications, diet, or health status.^[4] Warfarin is the second most common mismanaged therapeutic drug, requiring more than 40,000 emergency room visits per year and about $40 million to $60 million in additional medical costs per year.^[4] The therapeutic window for oral anticoagulant drugs is very narrow; therefore the accuracy for monitoring these drugs' INR is essential since inadequate dosing increases thrombotic risk and excessive doses significantly increase the bleeding risk.
Monitoring AVK anticoagulant therapy using the INR is in its final phases of a slow transition in the United States compared with most European countries routinely using the INR value. The INR is a mathematically transformed or calculated value converting the PT in seconds to a standard ratio value.^[1,2] The INR theoretically eliminates the differences in sensitivity of various PT reagents. However, within individual coagulation laboratories, the INR may not eliminate all of the variables of the PT assay, requiring local adjustment to make the reagent's INR more accurate with a specific instrument within the local environment.
Sensitivity to AVK anticoagulant therapy using the INR is the most important consideration when choosing a PT reagent.^[2] A single plasma sample from an anticoagulated patient may give clinically significant different PT clotting times when tested against a variety of PT reagents; theoretically the INR value should be the same. It is important to pick a reagent with clotting times based on a scientific rationale rather than one with clotting times "familiar" to your clinicians

 Concept of the INR

The differences in PT results are dependent upon the composition of the PT reagent.^[2] The reagent is composed of thromboplastin (tissue factor and phospholipid), extracted from a variety of sources (human and rabbit are the most common). Historically, each laboratory extracted thromboplastin from the human brain, but as commercial reagents were made available the major tissue source became rabbit brain. This is still used in a number of commercial reagents today. Now manufacturers are again starting to make reagents using human thromboplastin (placenta and recombinant).^[5] The therapeutic responsiveness of the PT reagent is different depending on the source and composition of the thromboplastin.^[1]
When the PT assay was first used to monitor AVK therapy, most providers based their therapeutic decisions on PT values in the range of 1.5 to 2.5 times the control value. However, now with the production of different reagent sensitivities with new sources of thromboplastin, the 1.5 to 2.5 range is not an accurate reflection of therapeutic anticoagulation.
In 1983, the World Health Organization (WHO) adopted a method to establish consistency of the PT value for patients on AVK.^[6] This mathematical expression of the PT value is termed INR.^[2] The INR calculation is based on the international sensitivity index (ISI) value specific to each PT reagent^[1] and is valid only for stable AVK anticoagulant therapy and only up to an INR of 4.5.^[1,2] An ISI value is determined for each thromboplastin reagent by comparing the responsiveness of the PT reagent with a WHO international reference preparation (IRP).^[6,7]
Theoretically, the INR of a patient receiving AVK therapy would be the same regardless of the reagent and instrument used or in which the laboratory the sample was tested.^[1,2,6] The specific PT reagent ISI value is determined using a WHO standard protocol comparing both PT reagent and IRP values from 20 normal individuals and 60 stable AVK individuals.^[6,7] The slope of the regression calculation (orthogonal) of the 2 values is the ISI value of the unknown reagent.^[2,6] Variation in the assigned ISI calculated by the manufacturer can vary +5%. This type of error can contribute to clinically different INR results.^[6]
The INR is calculated using the assigned ISI value and the mean normal PT (MNPT) value (Figure 1).^[2] The MNPT is determined by the laboratory using 20 to 40 (40 being optimal) healthy individuals reflecting the laboratory's patient base.^[2] The mean is calculated using the geometric mean rather than the arithmetic mean.^[2,8] The geometric mean assumes a non-normally distributed set of values. Geometric mean calculation transforms the data to log values before determining the mean. The arithmetic mean assumes a normally distributed normal population. The use of the arithmetic mean instead of the geometric mean can lead to a clinically significant difference in the MNPT and INR value.

                                         INR= ( Patient PT in sec / MN PT in sec ) ^ISI

Accuracy of the Manufacturer-assigned ISI

The ISI value reported in the PT reagent package insert has been determined by the manufacturer using the WHO standard method.^[6] However, there are potential sources of error associated with this assigned ISI value When these errors are compounded, a significant difference in the reported INR value and the true INR value can be found. These types of errors must be reduced by each laboratory. A manufacturer usually reports 2 ISI values for any PT reagent.^[9,10] The first is the "generic ISI" and is determined for instruments using the same end-point detection method but not a specific instrument. This ISI must be used when the reagent of 1 manufacturer is used on an instrument made by a second manufacturer. However, the accuracy of this ISI value for the reagent-instrument system may be of clinical concern. The second reported ISI value is specific to the PT reagent and instrument combination ("instrument-specific ISI"). In several studies, the accuracy of INR results was enhanced when instrument-specific ISI was used instead of the generic ISI.^[10,11] The range of discrepancy between the manufacturer-derived ISI and the local validated ISI can vary between +15% and 30%, thus making clinically significant differences in the INR value. Therefore the ISI value should be verified, especially in laboratories using generic ISI values. If the local validated ISI value is significantly different from the reported ISI, then the ISI must be determined locally.
The definition of verification is "the confirmation through the provision of objective evidence that the specified requirements have been fulfilled" (within a pre-established set of criteria).^[2,9] Verification is usually a 1-time process completed to confirm test performance before the INR system is used for patient testing. If significant differences in the INR test system are present, then calibration is performed followed by repeating the verification process. Calibration is "a set of operations establishing, under specified conditions, the relationship between true quantitative values indicated by the measuring test system."^[9] For the INR test system, if the verification is not different from the reported ISI value, then calibration does not need to be performed. If significant differences (>15%) are found between the ISI values, then calibration of the ISI is required, followed by re-verification to ensure INR accuracy.^[9,10]
The local verification and calibration (if necessary) of the ISI is performed with FDA-approved kits that provide all of the certified plasmas, the procedure, and data calculations. This ISI verification can be performed by any technologist or supervisor in all laboratories performing patient PT/INR results. The procedure usually takes 3 days of performing PT/INR testing on the certified plasmas and about 20 to 30 minutes of calculations that can be performed either by the manufacturer of the kit or through the manufacturer's Web-based program. This local verification and calibration procedure should be included in all new reagent and/or instrument contracts, cost per test, and cost per reportable result contracts. International sensitivity index verification and calibration (if necessary) should be performed (as part of the contract) at installation of the instrument, when starting a new reagent, for lot changes, and after instrument repair or internal or external QC issues. The procedure itself is relatively straightforward and has safeguards built in to provide a more accurate local ISI with clinically correct INR values.

Verification of the ISI in the Local Laboratory

The laboratory should not accept the initial ISI value assigned by the manufacturer as the local laboratory's working parameters, and conditions may significantly affect the patient's calculated INR results. With this in mind, it becomes the laboratory's responsibility to verify the validity of the ISI
Two basic methods for local verification of ISI are available.^[9] The first is the impractical method of using the WHO standard protocol. It is not feasible since it requires fresh plasma samples, an IRP, and the ability to perform the labor-intensive tilt tube assays. The second, more practical method uses certified plasmas to determine the ISI. These plasmas are purchased from the manufacturer of the reagent system or from an independent vendor especially for the reagent system. The verification kit should be part of the validation process for new installations, new reagents, and changes in reagents lots (Table 2). The procedure for verification per the provided instructions must be followed. The verification kit should be FDA approved following the established guidelines of Clinical and Laboratory Standards Institute (CLSI).^[2,9] In brief, the procedure requires a minimum of 3 certified plasmas in the range of 1.5 INR to 4.5 INR. These plasmas can be lyophilized or frozen. The certified plasmas are evaluated exactly as patient samples. The PT and INR values are determined for each plasma tested in duplicate once per day for 3 days. The INR values obtained are compared to the assigned INR of the certified plasma. If these values compare within 15%,^[2,9] then the ISI has been verified, and the PT reagent can be used with the assigned ISI value. If the verification procedure fails (INR values >15%), then a local calibration must be performed

Local System Calibration of the ISI for the Local Laboratory

If verification fails, then the laboratory must not report patient results until the correct ISI is determined.^[9] The laboratory must establish that: 1) instrument(s) was(were) working properly; 2) reagents were reconstituted correctly; 3) MNPT was determined accurately (geometric mean); and 4) no clerical or mathematical errors were made. If these are correct, then proceed to local calibration of the ISI.
Local calibration can be accurately determined using 2 methods: 1) calculating a local ISI, or 2) generating a PT/INR calibration line on which PT values are read as the INR value.^[9] Whichever method is used, the calibration kit must be FDA approved. The certified plasmas must be compatible for the reagents and instruments used in the laboratory.^[9] As an example, if the laboratory is using recombinant human thromboplastin, the calibration kit should be certified for use with human thromboplastin. The local ISI calibration procedure is a modification of the WHO protocol.^[8,9] The PT values for each of the certified plasmas are determined using the local PT reagent and instrument. The local PT values are plotted against the assigned PT values of the certified plasma and an orthogonal regression line is calculated. The ISI calibration is considered valid if the slope has a CV of <3%.^[9] The resulting slope of the line is the correct local ISI.^[8,9] The procedure is similar to the verification method. The certified plasmas must be run in duplicate for at least 3 days to account for variation due to random error.
necessary number of certified plasmas depends on a variety of factors, such as the source of the plasma (immuno-depleted or treated individual), type of plasma (frozen or lyophilized), single donor or multiple donors, and the IRP used for the certification of the plasma.^[9] The manufacturer of the calibration kit in consultation with and approval by the FDA has determined the minimum number of certified plasmas needed. Most manufacturers will help the local laboratory determine the ISI value through either the Internet or as a "send-in" service. The manufacturer must provide detailed documentation of these ISI determination calculations for accreditation documentation. Of important note, after local calibration, the ISI must again be re-validated to confirm that the calibration and changed ISI are truly correct.
The second method to determine the local ISI is the direct INR calibration line, which is independent of the ISI value and the MNPT.^[9] A disadvantage of this method is that many laboratory information systems and/or instrument systems are not programmed for calculating the INR by this method. Using this protocol, the PT values of certified plasmas are determined using the laboratory's system, also testing for 3 days in duplicate. The PT values determined locally are plotted on the y axis against the assigned certified plasma INR values (x axis). Using orthogonal regression, the best fit line is plotted. For a valid calibration curve, the r² value of the regression line must be >0.95. The patient's INR is mathematically or graphically determined from this calibration line. Significant changes in the reagent-instrument system, such as lot changes, instrumentation repair, QC validity changes, and proficiency testing problems will all require establishing the INR calibration line and recertification.^[9]

Conclusion

The INR is an important clinical tool for monitoring AVK therapy. The introduction of the INR has added several orders of magnitude of accuracy to anticoagulant monitoring. Still, more accuracy is needed to further reduce clinical problems associated with anticoagulation. To this end, the development of local reagent accuracy through the use of local ISI verification and ISI calibration adds even greater confidence to the correct reporting of INR values. The methods for ISI verification and the local ISI calibrations are just beginning to be used in the United States. The College of American Pathologists (CAP) Laboratory Accreditation program checklist (HEM.23220) requires documentation that the ISI is validated. The local ISI verification and calibration method fulfills that requirement. The methods may appear complex and the mathematics difficult, but kit manufacturers should assist with these calculations. Local determination of the ISI will significantly increase clinical confidence in oral anticoagulant monitoring.

References

• 1. Ansell J, Hirsh J, Hylek E, et al. Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th ed). Chest. 2008;133:160S-198S.
• 2. CLSI. One stage Prothrombin Time (PT) Test and Activated Partial Thromboplastin Time (APTT) Test; Approved Guideline. H47-A2. Wayne, PA: CLSI; 2008.
• 3. Wysowski DK, Nourjah P, Swartz L. Bleeding complications with warfarin use: A prevalent adverse effect resulting in regulatory action. Arch Intern Med. 2007;167:1414-1419.
• 4. Budnitz DS, Pollock DA, Weidenbach KN, et al. National surveillance of emergency department visits for outpatient adverse drug events. JAMA. 2006;296:1858-1866.
• 5. CAP. Coagulation (Limited) Survey Report (CGL-C). Chicago, IL: College of American Pathologists Proficiency Testing Program, 2009.
• 6. Poller L. International Normalized Ratios (INR): The first 20 years. J Thromb Haemost. 2004;2:849-860.
• 7. van den Besselaar AMHP, Poller L, Tripodi A. WHO Expert Committee on Biological Standardization. Forty-eighth Report. Guidelines for thromboplastins and plasma used to control oral anticoagulant therapy. WHO Technical Report Series. 1999;889:64-93.
• 8. van den Besselaar AMHP, Barrowcliffe TW, Houbouyan-Réveillard LL, et al. On behalf of the Subcommittee on Control of Anticoagulation of the Scientific and Standardization Committee of the ISTH. Guidelines on preparation, certification, and use of certified plasmas for ISI calibration and INR determination. J Thromb Haemost. 2004;2:1946-1953.
• 9. CLSI. Procedures for Validation of INR and Local Calibration of PT/INR Systems; Approved Guideline. H54-A. Wayne, PA: CLSI; 2005.
• 10. van den Besselaar AMHP, Houbouyan LL, Aillaud MF, et al. Influence of three types of automated coagulometers on the International Sensitivity Index (ISI) of rabbit, human and recombinant human tissue factor preparations: A multicenter study. Thromb Haemost. 1999;81:366-371.
• 11. Adcock DM, Johnston M. Evaluation of frozen plasma calibrants for enhanced standardization of the international normalized ratio (INR): A multi-center study. Thromb Haemost. 2002;87:74-79.

La anemia se asocia con rápido deterioro de la función renal en pacientes con insuficiencia cardíaca

                                                                           Dres.Bansal N, Tighiouart H, Sarnak MJ
                                                                  American Journal of Cardiology 99(8):1137-1142, Abr 2007

Introducción

Este trabajo evaluó si la presencia de anemia se asocia con deterioro de la función renal en pacientes con insuficiencia cardíaca (IC), con base en estudios previos que indicaron que este trastorno puede ser un factor de riesgo importante en sujetos con alteraciones de la función renal.
Se  analizaron los datos de Studies of Left Ventricular Dysfunction (SOLVD), un estudio aleatorizado que evaluó el uso de inhibidores de la enzima convertidora de angiotensina (IECA) en pacientes con disminución de la fracción de eyección.

Métodos

El SOLVD fue un estudio aleatorizado, a doble ciego, controlado con placebo, que reclutó entre 1986 y 1991 a 6797 sujetos y evaluó si el enalapril, un IECA, reducía la mortalidad en pacientes con fracción de eyección menor o igual a 35%. Los pacientes se dividieron en 2 grupos: tratamiento (IC sintomática, n = 2569) y prevención (IC asintomática, n = 4228). En este análisis se incluyeron ambos grupos.
La creatinina sérica basal se midió en 6 635 pacientes y el hematocrito en 6563 participantes. La primera se midió al inicio, a las 2 y 6 semanas, a los 4 meses y posteriormente cada 4 meses. La tasa de filtración glomerular (TFG) se calculó mediante la ecuación del estudio MDRD. La enfermedad renal crónica (ERC) se definió, de acuerdo con las normas de la National Kidney Foundation, como una TFG de hasta 60 ml/min/1.73 m2. La anemia se definió por un hematocrito < 36%. Finalmente, los pacientes que se incluyeron en el análisis totalizaron 6100.
Los factores basales que fueron considerados covariables incluyeron características demográficas (edad, raza y sexo), antecedentes clínicos (diabetes, hipertensión arterial y tabaquismo), mediciones de la función cardíaca (fracción de eyección, clase funcional de la New York Heart Association y la causa de disfunción ventricular izquierda), examen físico (presión arterial sistólica y peso), medicación usada (bloqueantes adrenérgicos beta, diuréticos, digoxina, antiagregantes plaquetarios y antiarrítmicos), grupo asignado (tratamiento vs. prevención) y aleatorización (enalapril vs. placebo).
El criterio de valoración principal del estudio fue un "rápido deterioro" de la función renal que se definió por el cuartilo de sujetos que presentaron una disminución más rápida de la TFG (mayor o igual a 6 ml/min/1.73 m2). Los criterios de valoración secundarios incluyeron el tiempo hasta alcanzar el doble del nivel de creatinina sérica y el tiempo hasta que se produjo un incremento de la creatinina sérica de 0.5 mg/dl o mayor. El tiempo de riesgo se calculó como el número de días transcurridos desde el inicio hasta que se produjera el primero de los siguientes eventos: 1) fecha de evaluación de la creatinina sérica cuando se alcanzaron los criterios de valoración secundarios, 2) fecha de la última evaluación de la creatinina sérica, 3) fecha de muerte o 4) fecha del último seguimiento

Resultados

Características basales

La población estudiada incluyó a 6360 sujetos. La edad promedio fue de 59 años y 14% eran mujeres. El 19% de los pacientes presentaba diabetes, 38% tenía hipertensión arterial, 31% ERC y 6% anemia. El hematocrito promedio fue 33.1% en el grupo con anemia y 43.4% en el grupo no anémico. La creatinina sérica al inicio era 1.3 mg/dl en el primer grupo y 1.2 mg/dl en el último (p < 0.001). El 41% del grupo anémico tenía ERC en comparación con el 31% de los sujetos sin anemia (p < 0.001). En la etapa basal, entre los pacientes no anémicos había mayor proporción de hombres y menor porcentaje de pacientes hipertensos o diabéticos.

Criterios de valoración principales

La mediana del período de seguimiento del estudio fue de 2 años. La pendiente de la TFG promedio fue de -3.33 ml/min/1.73 m2/año y la de la TFG mediana de -1.51 ml/min/1.73 m2/año.
El 32% de los pacientes con anemia alcanzó el criterio de valoración principal de una disminución de la TFG > 6 ml/min/1.73 m2/año, en comparación con el 25% de los pacientes sin anemia (p = 0.002). En el análisis multivariado, la anemia fue un factor de riesgo significativo para el rápido deterioro de la función renal; el riesgo para una rápida disminución de la TFG fue 30% mayor en pacientes con anemia que en aquellos no anémicos. Esta relación se modificó por el nivel de función renal (p < 0.001 para la interacción entre anemia y ERC). En sujetos con ERC, la probabilidad de una rápida disminución de la TFG fue 71% mayor en aquellos que presentaban anemia, mientras que en los pacientes sin ERC la probabilidad de un rápido descenso de la TFG fue sólo 16% mayor.

Criterios de valoración secundarios

En el 4% de los pacientes con anemia se observó un incremento al doble del nivel de creatinina en comparación con el 2% de los sujetos no anémicos (p = 0.01).
La presencia de anemia se asoció con un incremento significativo en el riesgo de duplicar la creatinina sérica (hazard ratio [HR]: 1.74). La interacción entre la función renal basal y la anemia permaneció estadísticamente significativa (p = 0.04) y esta última se asoció con un marcado incremento en el riesgo para la duplicación de los niveles séricos de creatinina en pacientes con ERC (HR: 3.54), pero sólo con una tendencia al aumento en sujetos sin esta enfermedad (HR: 1.20).
El 21% de los pacientes con anemia tuvo un incremento de 0.5 mg/dl en la creatinina sérica en comparación con el 14% de los sujetos no anémicos (p < 0.001). La presencia de anemia se asoció en forma significativa con un incremento de 0.5 mg/dl en la creatinina sérica (HR: 1.44). En sujetos con ERC, la anemia se asoció con un significativo incremento del riesgo (HR: 1.84), mientras que los pacientes sin ERC tuvieron un ligero aumento en el riesgo (HR: 1.18).

Análisis de sensibilidad

Cuando se utilizó la definición de la Organización Mundial de la Salud para el criterio de valoración principal de una disminución de la pendiente > 6 ml/min/1.73 m2/año, la presencia de anemia se asoció con un odds ratio de 1.20. Para el criterio de valoración secundario de duplicar el nivel de creatinina, la presencia de anemia se asoció con un HR de 1.67, mientras que para incrementar en 0.5 mg/dl el nivel de creatinina estuvo asociada con un HR de 1.44

Discusión

Este estudio demostró que la anemia se asocia con una progresión más rápida de enfermedad renal en pacientes con IC y que el nivel de función renal basal modifica este riesgo.
Estudios previos evaluaron la anemia como riesgo en la progresión de la enfermedad renal. Un estudio separado del SOLVD, cuyo objetivo fue evaluar el efecto del deterioro en la función renal sobre los criterios de valoración, demostró que un menor nivel de hematocrito se relacionó con una mayor probabilidad de reducción en la TFG > 15 ml/min/1.73 m2/año.
Entre las explicaciones por las cuales la anemia promueve un deterioro más rápido de la función renal se puede citar la hipoxia que provoca una provisión inadecuada de oxígeno a las células tubulares renales y causa isquemia crónica y eventual pérdida de nefrones. Además, la hipoxia incrementa la actividad de los fibroblastos intersticiales del riñón y conduce a aumento de la fibrosis intersticial y daño renal. Otras teorías sugieren que la hipoxia causada por la anemia puede activar el sistema simpático y el sistema renina-angiotensina-aldosterona, con efectos deletéreos sobre el corazón y los riñones.
La anemia puede no estar asociada en forma causal con la progresión de la enfermedad renal sino más bien reflejar la gravedad de la IC. Es decir, los pacientes con IC grave pueden ser más susceptibles a la progresión de esta enfermedad y tienen menores niveles de hematocrito.

Experiencia de colegas de República Oriental del Uruguay.
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Sciuto J, Castro M, Castillo V, Gallo JC, Barindelli A, Lic NC La Ruina L, Lic NC Da Fonseca F

              Laboratorio de Emergencia, Centro de Tratamiento Intensivo, Hospital de Clínicas, UDELAR-Uruguay.

INTRODUCCION E IMPORTANCIA DEL TEMA

El aumento de la necesidad de estudios al pie de la cama en pacientes críticos ha determinado en los últimos tiempos un enorme incremento de la utilización de los analizadores multiparamétricos. Los mismos aportan información de fundamental interés a partir de un volúmen mínimo de sangre, lo que ha transformado a ésta tecnología en un recurso de amplia utilización e interés creciente. Asimismo  la inmediatez e importancia de los analitos aportados por un equipo multiparamétrico  requiere de una calidad absoluta en los valores obtenidos, razón por la cual resulta imprescindible asegurar las condiciones preanalíticas de las muestras analizadas. En nuestro medio está muy difundido el uso de la solución de heparina sódica para la preparación de las muestras a medir por el analizador multiparamétrico. La heparina  es un carbohidrato complejo perteneciente a la familia de los glicosaminglicanos y debe su efecto anticoagulante a la presencia de una secuencia de pentasacáridos sulfatados que se unen ávidamente a la Antitrombina III. Esta es una proteína del plasma que actúa inhibiendo la acción de diversos factores dela cascada de la coagulación: XIa, Xa, IXa y IIa (trombina). La desventaja mayor es el riesgo de dilución excesiva de la muestra con la solución de anticoagulante.
La presencia del espacio muerto de la jeringa, (sector donde se inserta la aguja) y hasta donde llega el émbolo para expulsar el resto de líquido, suele dejar inevitablemente una cantidad no especificada de anticoagulante, que puede ser de 100 microlitros o más, según el tamaño y el tipo de jeringa. Si la cantidad obtenida de sangre resulta menor a 2 ml (caso de los neonatos), la proporción óptima con el anticoagulante se pierde. Sumado a  eso, un defecto en la maniobra de expulsión de la heparina líquida, lleva a una dilución mayor de 5%con una concentración final de heparina mayor a 50 UI/ml. De esta manera, los efectos observables en los analitos, podrían deberse a :1) la presencia de la heparina per- se, y 2)  el efecto de dilución de la sangre.
El uso de jeringas con heparinato de litio tamponado con calcio liofilizado evitaría todos estos errores y es el procedimiento recomendado por las normas CLSI.
En nuestro medio (Hospital de Clínicas, UDELAR) empleamos para la realización de las gasometrías arteriales y venosas, jeringas heparinizadas de forma manual con heparina sódica y de acuerdo a un protocolo establecido para su preparación . Nos  hemos propuesto investigar la correlación de los valores de Na+, K+, Ca iónico y Cl-  aportadas por muestras extraídas en las jeringas preparadas de forma manual con heparina sódica y aquellas aportadas por las muestras extraídas con jeringa de heparina tamponada con calcio y liofilizada (BD A-Line, Becton-Dickinson) , para establecer una recomendación respecto a las condiciones preanalíticas a instituir en nuestro medio.

OBJETIVOS:

Comparar los valores del ionograma (Na+, K+, Ca+ iónico y Cl-) aportados por muestras de sangre venosa extraída con jeringa de heparina sódica de preparación manual con aquellos obtenidos con jeringa de heparina de heparina litio tamponada con calcio y liofilizada (BD A-Line, Becton-Dickinson) .

MATERIAL Y METODOS.

Población : Se obtuvieron un total de 182 muestras correspondientes a 91 individuos (2 muestras por paciente) para la realización de gasometrías venosas , de pacientes internados en el Centro de Tratamiento Intensivo (CTI) del Hospital Universitario, Hospital de Clínicas (HC), a quienes se realiza el procedimiento diariamente dentro de su rutina habitual. Procedimiento; Se procedió de la manera habitual dentro del protocolo de extracción. Muestra 1) se preparó con jeringa descartable con solución de heparina sódica 25.000 UI/ 5ml siguiendo el método habitual que consiste en obtener dicha solución directamente de la ampolla y descartar 3 veces eliminando todo el exceso de líquido antes de realizar la punción . A continuación se obtuvo  la Muestra 2) de sangre venosa con la jeringa de heparina tamponada con calcio y liofilizada (BD A-Line, Becton-Dickinson). Ambas muestras se procesaron de manera inmediata a su recolección en el analizador Multiperfil ABL 735 Flex (Radiometer), CV% Na= 0,47, K+ = 0,67, Ca+ = 1,47 y Cl - = 0,57%) a través del mismo operador.  Se procedió a la recolección de los datos obtenidos a través de una planilla de Excel creada para los propósitos del presente estudio .Análisis Estadístico: Las variables en estudio son ambas cuantitativas y fueron analizadas con mediana, recorrido intercuartílico, mínimo y máximo, se estudia a priori el supuesto de ajuste a la distribución normal de cada una de ellas llevado a cabo a través del test de Kolmogorov - Smirnov. Los gráficos empleados fueron diagrama de dispersión (scatter plot) y el gráfico de Bland - Altman. Se empleó el test no paramétrico de Wilcoxon de comparación de medias de grupos pareados. Para estudiar la correlación entre dos variables numéricas con previa verificación de distribución normal se empleó el coeficiente de correlación de Spearman. El test t de Student para contrastar los coeficientes de la recta de regresión fue realizado junto a los intervalos de confianza al 95% (IC_95%). Los software informáticos utilizados fueron Microsoft Excel y SPSS versión 18.0; se consideró significativo un valor p < 0,05. 

RESULTADOS

                                      Na (Sodio)

Se estudiaron 91 pacientes, empleándose los materiales preanalíticos correspondientes a jeringa artesanal de preparación manual con heparina sódica y  jeringa comercial de heparina de litio  tamponada con calcio y liofilizada. El estudio se llevó a cabo entre los pacientes internados en el Centro de Tratamiento Intensivo del Hospital de Clínicas en el período correspondiente al mes de setiembre de 2010.                                                                                                                      
La descriptiva de ambos métodos se indica en la tabla número 1; y a través del test de Kolgomorov-Smirnov (p=0,003  para jeringa comercial y p=0,008 para jeringa artesanal) rechazamos la hipótesis de distribución normal de ambas distribuciones.

Tabla 1. Estadística descriptiva de la variable Sodio (Na) en los 91 pacientes estudiados según los métodos jeringa artesanal y jeringa comercial, Hospital de Clínicas Manuel Quintela, setiembre 2010. 

A través del test de Spearman encontramos asociación estadística entre ambos métodos  (r_o= 0,993, p< 0,0001).
En el gráfico número 1 se indica el diagrama de dispersión de Bland-Altman donde observamos que existe un buen nivel de acuerdo entre ambos métodos. A través del gráfico número 2 (scatter plot) observamos que existe un ajuste adecuado entre ambas rectas (la de regresión de los puntos observados y la esperada). La recta de regresión observada es; y = 0,969 + x, y a través del estadístico t de Student verificamos que el intercepto de la recta de regresión no difiere significativamente de 0 (p=0,535) ni su coeficiente angular del valor 1 (p=1), objetivando que ambos métodos presentan un fuerte grado de correlación y acuerdo.

Gráfico 1. Diagrama de Bland - Altman de la variable Sodio (Na) en los 91 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas "Manuel Quintela", setiembre 2010.

Gráfico 2. Scatter Plot y rectas de regresión: observada y esperada bajo el supuesto de ajuste perfecto de ambos métodos, para la variable Sodio (Na) en los 91 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas "Manuel Quintela", setiembre 2010.

                Recta de regresión observada (y = 0,969 + x)

                Recta de regresión esperada (y = x)

En la tabla número 2 se presentan los coeficientes de la recta de regresión junto con sus valores p e IC_{95% .}

Tabla 2. Coeficientes de la recta de regresión e IC_95% para los mismos, variable Sodio (n=91), según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas "Manuel Quintela", setiembre 

CONCLUSIONES

Ambos jeringas poseen un alto grado de acuerdo y buena correlación para la medición del sodio, por lo cual pueden ser utilizadas indistintamente para el procesamiento del mismo mediante la utilización del analizador multiparamétrico ABL 735 Flex (Radiometer). 

                                                                 K (Potasio)

 La descriptiva de ambos métodos se indica en la tabla número 1; y a través del test de Kolgomorov-Smirnov (p=0,04  para jeringa comercial y p=0,103 para jeringa artesanal) rechazamos la hipótesis de distribución normal de ambas distribuciones.

Tabla 1. Estadística descriptiva de la variable Potasio (K) en los 91 pacientes estudiados según los métodos jeringa artesanal y jeringa comercial, Hospital de Clínicas "Manuel Quintela", setiembre 2010. 

Existe asociación entre ambos métodos a través del test de Spearman (r_o= 0,964, p< 0,0001).  A través del gráfico número 1 se indica el diagrama de dispersión de Bland-Altman donde observamos que existe un buen nivel de acuerdo entre ambos métodos. A través del gráfico número 2 (scatter plot) observamos que existe un ajuste adecuado entre ambas rectas (la de regresión de los puntos observados y la esperada).La recta de regresión observada es; y = 0,199 + 0,943 x.

Gráfico 1. Diagrama de Bland - Altman de la variable Potasio (K) en los 91 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas "Manuel Quintela", setiembre 2010.

 Promedio de las diferencias                   
Promedio de las diferencias ± 2 desviaciones estándar.

Gráfico 2. Scatter Plot y rectas de regresión: observada y esperada bajo el supuesto de ajuste perfecto de ambos métodos, para la variable Potasio (K) en los 91 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas " Manuel Quintela", setiembre 2010.

                Recta de regresión observada (y = 0,199 + 0,943x)
                Recta de regresión esperada (y = x)

 En la tabla número 2 se presentan los coeficientes de la recta de regresión junto con sus valores p e IC_95%  a través del test t de Student.

 Tabla número 2. Coeficientes de la recta de regresión e IC_95% para los mismos, variable Potasio (n=91), según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

 CONCLUSIONES

Ambas jeringas (comercial y de preparación manual) poseen un alto grado de acuerdo y correlación para la medición del ión K+, razón por la cual pueden ser empleadas de manera indistinta para su procesamiento en las condiciones habituales en el CTI del Hospital de Clínicas, mediante el analizador multiperfil ABL 735 Flex (Radiometer).

                                                         Ca (Calcio)

 La descriptiva de ambos métodos se indica en la tabla número 1; y a través del test de Kolgomorov-Smirnov (p=0,047  para jeringa comercial y p=0,006 para jeringa artesanal) rechazamos la hipótesis de distribución normal de ambas distribuciones.

Tabla  1. Estadística descriptiva de la variable Calcio (Ca) en los 90 pacientes estudiados según los métodos jeringa artesanal y jeringa comercial, Hospital de Clínicas "Manuel Quintela", setiembre 2010.

Encontramos asociación entre ambos métodos a través del test de Spearman (r_o= 0,691, p< 0,0001). En el gráfico número 1 se indica el diagrama de dispersión de Bland-Altman donde observamos que existe un buen nivel de acuerdo entre ambos métodos. A través del gráfico número 2 (scatter plot) observamos que existe un ajuste adecuado entre ambas rectas (la de regresión de los puntos observados y la esperada). La recta de regresión observada es; y = 0,074 + 0,857 x, sin embargo a través del estadístico t de Student verificamos que el intercepto de la recta de regresión no difiere significativamente de 0 (p=0,472) ni su coeficiente angular del valor 1 (p=0,098), objetivando que ambos métodos presentan un grado de correlación y de acuerdo estadístico. A pesar de lo previamente expuesto se verificaron hallazgos indicadores de un eventual sesgo entre las mediciones de ambos preparados en estudio, que ameritó un análisis estadístico adicional.

Gráfico  1. Diagrama de Bland - Altman de la variable Calcio (Ca) en los 91 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

                     Promedio de las diferencias. 
                    Promedio de las diferencias ± 2 desviaciones estándar.

Gráfico  2. Scatter Plot y rectas de regresión: observada y esperada bajo el supuesto de ajuste perfecto de ambos métodos, para la variable Calcio (Ca) en los 90 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

                Recta de regresión observada (y = 0,074 + 0,857x)
                Recta de regresión esperada (y = x)

En la tabla número 2 se presentan los coeficientes de la recta de regresión junto con sus valores p e IC_95%  a través del test t de Student encontrando un ajuste estadísticamente significativo y adecuado con un alto nivel de acuerdo entre ambos métodos en estudio.

Tabla número 2. Coeficientes de la recta de regresión e IC_95% para los mismos, variable Calcio (n=90), según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

Cuando se categorizó la variable calcemia (tabla 3) según los valores de referencia: < a 1,14 mEq/l = hipocalcemia, entre 1,14 - 1,30 = normocalcemia y >  1,30= hipercalcemia, se encontraron elevadas discrepancias según la jeringa empleada para su medición. En la tabla numero 3 se muestra la distribución de esa variable según la jeringa  utilizada. Posteriormente se realizó el test kappa de acuerdo entre dos métodos encontrando un coeficiente de acuerdo (Kappa) significativamente distinto que cero pero dado su valor (0,199) lo catalogamos de bajo acuerdo (< 0,20). Por último se estudió los posibles puntos de corte para el diagnóstico de hipocalcemia encontrando que la jeringa artesanal posee un punto de corte óptimo en el valor 1,02 mEq/l, lo cual refleja una diferencia importante respecto al valor de referencia de 1,14 mEq/l. Cuando se comparan los valores de calcio iónico aportados por la jeringa artesanal con respecto a los medidos con la jeringa  comercial, encontramos un elevado número de falsos positivos para hipocalcemia (68,2 %). En nuestro estudio no hemos encontrado hipercalcemias, por lo que no podemos establecer si ese comportamiento se repite en valores por encima de los rangos de referencia. Asumimos que en caso de verificarse el mismo comportamiento en los rangos elevados de calcio iónico, se podría correr el riesgo de subestimar una hipercalcemia, de acuerdo con el sesgo a la izquierda que determina valores inferiores a los verdaderos cuando se emplea la jeringa de heparina sódica.

Tabla 3. Cuadro de doble entrada entre los resultados de ambas pruebas, según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.  

* Valor del test Kappa: 0,199 (p=0,002).

Conclusiones

Es un hecho conocido que los valores de calcio iónico cuando se utilizan preparados con heparina sódica para su medición presentan dos fuentes de error importantes : 1) El asociado a la dilución a la que el calcio es particularmente sensible dada su pequeña concentración en plasma (1,1-1,3 mEq / l) y 2) El debido a la capacidad de la heparina de atrapar calcio, con lo cual la disminución del calcio es directamente proporcional al aumento de concentración de heparina en la muestra.
Como era de esperarse ambas jeringas (heparina sódica y heparinato de litio tamponado con calcio y liofilizado)  poseen un alto grado de desacuerdo en la medición del calcio iónico y los preparados preanalíticos (jeringa comercial y jeringa de heparina sódica) muestran amplias diferencias en los valores obtenidos para el mismo, con un sesgo marcado hacia valores inferiores por parte de la jeringa de heparina sódica.
Se hace necesario en éstos casos disponer de la jeringa comercial de heparina de litio tamponada con calcio y liofilizada para la medición del calcio iónico teniendo en cuenta la importancia de obtener valores exactos por su importancia para el diagnóstico y seguimiento en pacientes críticos.

                                                                   Cl (Cloro)

 La descriptiva de ambos métodos se indica en la tabla número 1; y a través del test de Kolgomorov-Smirnov (p=0,037  para jeringa comercial y p=0,003 para jeringa artesanal) rechazamos la hipótesis de distribución normal de ambas distribuciones.

Tabla 1. Estadística descriptiva de la variable Calcio (Ca) en los 90 pacientes estudiados según los métodos jeringa artesanal y jeringa comercial, Hospital de Clínicas Manuel Quintela, setiembre 2010.

Encontramos asociación entre ambos métodos a través del test de Spearman (r_o= 0,990, p< 0,0001). A través del gráfico número 1 se indica el diagrama de dispersión de Bland-Altman donde observamos que existe un buen nivel de acuerdo entre ambos métodos.            A través del gráfico número 2 (scatter plot) observamos que existe un ajuste adecuado entre ambas rectas (la de regresión de los puntos observados y la esperada).                   La recta de regresión observada es; y = 2,189 + 0,979 x, sin embargo a través del estadístico t de Student verificamos que el intercepto de la recta de regresión no difiere significativamente de 0 (p=0,125) ni su coeficiente angular del valor 1 (p=0,084), objetivando que ambos métodos presentan un grado de correlación y de acuerdo.

Gráfico 1. Diagrama de Bland - Altman de la variable Cloro (Cl) en los 90 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

                     Promedio de las diferencias. 
                     Promedio de las diferencias ± 2 desviaciones estándar.

Gráfico 2. Scatter Plot y rectas de regresión: observada y esperada bajo el supuesto de ajuste perfecto de ambos métodos, para la variable Cloro (Cl) en los 90 pacientes estudiados según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

                Recta de regresión observada (y = 2,189 + 0,979x)
               Recta de regresión esperada (y = x)

En la tabla número 2 se presentan los coeficientes de la recta de regresión junto con sus valores p e IC_95%  a través del test t de Student encontrando un ajuste estadísticamente significativo y adecuado con un alto nivel de acuerdo entre ambos métodos en estudio.

Tabla  2. Coeficientes de la recta de regresión e IC_95% para los mismos, variable Cloro (n=90), según los métodos jeringa comercial y jeringa artesanal, Hospital de Clínicas Manuel Quintela, setiembre 2010.

 Conclusiones

Ambos preparados preanalíticos (jeringa de heparina sódica y comercial de heparina de litio balanceada con calcio y liofilizada)  poseen un alto grado de acuerdo y correlación para la medición del cloro a través del analizador multiperfil ABL 735 Flex (Radiometer), en las condiciones habituales del CTI  del Hospital de Clínicas.

DISCUSION.

La jeringa de preparación manual con heparina sódica puede resultar aceptable para la medición del Na+, K+, y Cl- a través del analizador multiperfil ABL 735 Flex, Radiometer. Lo mismo no sucede en relación con el calcio iónico, razón por la cual recomendamos el empleo de jeringas de heparina tamponada y liofilizada para la medición del antedicho parámetro.

Referencias bibliográficas

• 1. Richard C,Dennis MD,Ronald NG et al. Effect of simple dilutions on arterial blood gas determinations. CritCareMed.Vol.13,N.12.
• 2. Multiprofile blood gas method comparison studies. Bloodgas.org. Quality assurance.
• 3. National Committee for Clinical Laboratory Standards (NCCLS). Document GP2-A4 Clinical Laboratory
• 4. Technical Procedure Manuals; Approved Guideline-Fourth Edition. Pennsylvania 19087-1898, USA. 2002
• 5. Sigaard Andersen O. Sampling and storing of blood for determination of acid base status. Scand J Clin &Lab Invest 1961; 13:196-204.
• 6. National Comitee for Clinical Laboratory Standards(NCCLS). Procedures for collection of Arterial Blood
• 7. Specimens. 4th Edition, H11- A4 NCCLS: Pennsylvania USA. 2004.
• 8. Hamilton R, Crockett A, Alpers J. Arterial blood gas analysis: potential errors due to the addition of heparin. Anaesth Intensive Care 1978; 6: 251-55.
• 9. Dake MD, Peters J, Theague R. The effect of heparin dilution on arterial blood gas analysis. Westwrn J Med 1984; 140: 792-93.
• 10. Hutchinson A, Ralston S, Dryburg F, et al. Too much heparin: possible source of error in blood gas analysis.BMJ 1983; 287:1131-32.
• 11. Gayed A, Marino E, Dolnski E. Comparision of the effects of dry and liquid heparin on neonatal arterialblood gases. Am J Perinatol 1992; 9:159-61
• 12. Shin CS, Chang CH, Kim JH. Liquid heparin anticoagulant produces more negative bias in the

determination of ionized magnesium than ionizedcalcium. Yonsei Med J 2006; 47:191-95.

• 13. Toffalette J. Use of novel preparation of heparin to eliminate interference in ionized calcium

measurements: have all problems been solved. Clin Chem 1994; 40:508-09.

• 14. Sachs CH, Rabouine PH, Chaneac M, et al. Preanalytical errors in ionized calcium measurements induced by the use of liquid heparin. Ann Clin Biochem 1991;28:167-73.

_________________________________________________________________________________

 La publicacion no implica coincidir totalmente con las conclusiones que se presentan 

Política de antibióticos en pacientes críticos

 F. Álvarez Lerma a, R. Sierra Camerino b, L. Álvarez Rocha c, Ó. Rodríguez Colomo d

a Servicio de Medicina Intensiva, Hospital del Mar, Barcelona, España

b Servicio de Medicina Intensiva, Hospital Puerta de Mar, Cádiz, España

c Servicio de Medicina Intensiva, Hospital Juan Canalejo, A Coruña, España

d Servicio de Medicina Intensiva, Hospital Clínico Universitario de Valencia, Valencia, España

                                                                                              Medicina Intensiva Vol.34 Núm. 09 – 2010

Resumen

El conjunto de normas y estrategias desarrolladas para mejorar y optimizar el empleo de los antimicrobianos recibe el nombre de política de antibióticos. Los pacientes críticos ingresados en servicios de medicina intensiva presentan unas características especiales (gravedad, agentes patógenos, alteración de órganos o sistemas) que justifican el empleo de los antibióticos de forma diferencial al de otros pacientes hospitalizados. La influencia y el impacto de los antibióticos se observa en los pacientes que los reciben (respuesta clínica, evolución) y en el ecosistema que rodea al paciente (flora hospitalaria). Este impacto es especialmente visible en los pacientes críticos y en la flora endémica de las unidades de cuidados intensivos.
En este artículo se describe un conjunto de normas (decálogo de normas) y estrategias (desescalada terapéutica, ciclado de antibióticos, tratamiento anticipado y parámetros farmacocinéticos/farmacodinámicos) que se han aplicado y desarrollado en los pacientes críticos para optimizar el empleo de los antimicrobianos con el objetivo de conseguir la máxima efectividad y la mínima morbilidad.

Palabras clave: Política de antibióticos. Desescalada teraupética. Ciclado de antibióticos. Tratamiento anticipado.

«La prescripción de antibióticos no debe ser nunca un acto rutinario sino que debe estar precedida, en todos los casos, de actos de reflexión, antes, durante y después de su administración».

Introducción

Los antimicrobianos son fármacos utilizados con gran frecuencia en los servicios o unidades de cuidados intensivos (UCI). En la última década se ha demostrado que la administración precoz de antimicrobianos con espectro adecuado influye a corto plazo en una evolución favorable de los pacientes críticos^1,2,3,4, mientras que a largo plazo, los antimicrobianos favorecen la aparición de flora emergente y condicionan cambios en las resistencias en aquellos patógenos que forman parte del ecosistema de los hospitales^5,6. A lo largo de los años, se ha propuesto un conjunto de normas y estrategias para mejorar y optimizar su empleo^7,8,9, lo que en conjunto recibe el nombre de política de antibióticos.

Para desarrollar en un hospital un programa de política de antibióticos es necesario la participación activa de todo el personal sanitario, tanto la de aquellos dedicados al control y la vigilancia de las infecciones relacionadas con la asistencia sanitaria (antes llamadas infecciones nosocomiales) como la de los dedicados a su prevención o tratamiento. En algunas UCI existen médicos que emplean parte de su tiempo en funciones de control, vigilancia, tratamiento y prevención de las infecciones relacionadas con la asistencia sanitaria y controlan la utilización de los antibióticos, lo que ha supuesto un impulso a la consolidación de la política de antibióticos en estas áreas de alto riesgo. En colaboración con otras especialidades básicas (microbiología, farmacia, farmacología, medicina preventiva) son los responsables de diseñar las estrategias terapéuticas más adecuada a la situación de cada UCI.

En este artículo se incluye un conjunto de normas que, a juicio de los autores de este documento, son básicas para la utilización de antibióticos en pacientes críticos (tabla 1) así como aquellas estrategias que se han propuesto con la finalidad de optimizar su empleo y disminuir la morbilidad relacionada con su uso. Todo esto constituye la base de la política de antibióticos y del uso racional de los antimicrobianos en cualquier UCI. Para su elaboración no se ha seguido ninguna metodología específica, por lo que no se incluye ningún tipo de graduación de evidencia ni de recomendación.

Tabla 1. Decálogo de normas de política de antibióticos en pacientes críticos

Normas básicas del uso de antimicrobianos en pacientes críticos. Decálogo de normas

Primera norma. «Utilizar antibióticos solo cuando existe la sospecha clínica o microbiológica de una infección»

Los antibióticos solo deben utilizarse, con finalidad terapéutica, cuando existe la sospecha clínica o microbiológica de infección, aunque en los pacientes críticos puede ser difícil diferenciar entre sepsis (respuesta inflamatoria sistémica frente a la infección) y síndrome de respuesta inflamatoria sistémica frente a otros estímulos inflamatorios de naturaleza no infecciosa (traumatismo, poliartritis, pancreatitis, hemorragia, entre otras) y que, inicialmente, cursan con la misma expresividad clínica^10,11. Asimismo, no debe ser motivo de inicio de tratamiento antibiótico el aislamiento de microorganismos en algunas muestras (esputo, aspirado traqueal, heces, piel) en las que existe de forma habitual una flora endógena o el aislamiento en sangre o en muestras pulmonares, incluso en las obtenidas con métodos invasivos (catéter telescopado protegido, lavado broncoalveolar, etc.) de patógenos escasamente virulentos (Staphylococcus coagulasa negativos, Corynebacterium sp.). En todos los casos, es preciso razonar y relacionar la situación clínica del paciente con los hallazgos microbiológicos.

En los casos de sospecha clínica de infección respiratoria de vías bajas (esputo purulento, leucocitosis, fiebre), sin coexistencia de infiltrados radiológicos, en pacientes con ventilación mecánica es conveniente la realización de exploraciones complementarias para confirmar el diagnóstico de infección. En los pacientes con fiebre de foco desconocido, siempre que no haya una respuesta sistémica grave, el recambio o la retirada de catéteres puede ser suficiente para solucionar el proceso infeccioso. La administración de antibióticos, sin esperar la respuesta al cambio de los catéteres, es uno de los motivos por los que ha aumentado el consumo de glucopéptidos en las áreas de cuidados intensivos.

Una parte importante de los antimicrobianos utilizados en las UCI se prescriben como profilaxis. En estos casos se recomienda su uso de acuerdo con protocolos consensuados en el hospital y por cortos períodos de tiempo. Existen estudios que demuestran la eficacia de la administración de antibióticos locales no absorbibles en el tubo digestivo y en la orofaringe para prevenir la aparición de infecciones endógenas tardías en pacientes con ventilación mecánica^{12,13,14,15,16} o la administración de antibióticos sistémicos para prevenir la aparición de infecciones respiratorias precoces en pacientes en coma que precisan intubación de la vía aérea¹⁷. A pesar de las numerosas evidencias acumuladas, la utilización de antibióticos locales no se ha generalizado en las UCI y se ha reservado su empleo en pacientes de riesgo (trasplante hepático o pulmonar, traumáticos graves o quirúrgicos complejos)^18,19,20. En pacientes con pancreatitis aguda grave se había recomendado hasta hace poco el empleo de antibióticos para prevenir la aparición de complicaciones infecciosas²¹ sin embargo, estudios recientes, mejor diseñados, han demostrado su falta de efectividad²².

Segunda norma. «Obtener muestras de los tejidos infectados antes de iniciar un tratamiento con antibióticos»

En los pacientes críticos, la prescripción de antibióticos sin obtener muestras de los tejidos infectados y de sangre no está justificada en ninguna ocasión. Antes de administrar la primera dosis hay que hacer todo lo posible para obtener muestras para cultivos (incluidas al menos 2 muestras de sangre), siempre que no se retrase la administración del antibiótico. El aislamiento de agentes patógenos permite confirmar la infección en determinadas situaciones clínicas en las que pueden existir dudas diagnósticas (bacteriemia, neumonía, infección del tracto urinario). Por eso, el inicio de un tratamiento con antibióticos debe ir precedido, en todos los casos, de la obtención de muestras adecuadas de cada foco y se deben utilizar, en los casos necesarios, técnicas invasivas e incluso quirúrgicas. Cuando no sea posible la utilización de procedimientos seguros para la obtención de muestras en los se requiere la colaboración de otros especialistas, se deben obtener muestras consideradas menos eficaces o con menos seguridad diagnóstica, como las secreciones traqueales (aspiración traqueal simple), el exudado abdominal (drenajes, fístulas o heridas externas) o el exudado orofaríngeo, nasal o rectal. La utilización de técnicas invasivas «ciegas» (catéter telescopado, lavado broncoalveolar), sobre todo las protegidas frente a la contaminación, ha demostrado ser de utilidad para el diagnóstico de infecciones respiratorias^23,24.
Si el paciente está utilizando antibióticos, en el momento de detectarse una nueva infección deben tomarse las muestras con la máxima rapidez, sin esperar a que disminuya la acción de los antibióticos circulantes, ya que es muy posible que los patógenos causantes de la infección sean resistentes a los antibióticos que recibe. En estos casos se aconseja la obtención de las muestras en el momento previo a la administración de la siguiente dosis del antibiótico, que se corresponde con su mínima concentración plasmática.

Tercera norma. «Elegir los antibióticos empíricos utilizando protocolos terapéuticos consensuados»

Los antibióticos empíricos que se utilizan en la mayoría de los procesos infecciosos diagnosticados en pacientes críticos deben estar incluidos en los protocolos de actuación, previamente elaborados en cada UCI. En la tabla 2 se incluyen aquellos procesos infecciosos en los que es aconsejable disponer de protocolos terapéuticos empíricos en las UCI.

Tabla 2. Procesos infecciosos frente a los que es aconsejable disponer de protocolos terapéuticos específicos

Los protocolos contemplan diferentes situaciones clínicas (tratamiento de primera y segunda elección, tratamiento de rescate), incluyen algunas situaciones especiales de los pacientes (insuficiencia renal, alergia a betalactámicos, embarazo) y recomiendan los antibióticos, dosis y vías de administración más adecuados para el tratamiento de los patógenos esperados en cada zona geográfica, hospital o UCI. En los pacientes críticos, en todos los casos se empleará la vía intravenosa para asegurar, lo antes posible, una elevada concentración plasmática y tisular; se respetará la dosificación máxima recomendada, que se asocia con concentraciones plasmáticas óptimas, y se realizarán los ajustes necesarios según la función renal de los pacientes.
En la elaboración de los protocolos es aconsejable que intervengan todos los especialistas comprometidos en la prevención y el tratamiento de las infecciones (microbiólogos, farmacéuticos, farmacólogos, infectológos, preventivistas e intensivistas), aunque la responsabilidad de su aplicación, así como la realización de auditorías sobre su cumplimiento, corresponde al médico de medicina intensiva experto en enfermedades infecciosas.
La información periódica de la frecuencia de los agentes patógenos que predominan en las muestras orgánicas más significativas, así como conocer su sensibilidad a los antimicrobianos, permite modificar los protocolos terapéuticos empíricos y ajustarlos a la realidad epidemiológica de cada área. La colaboración y la comunicación con el servicio de microbiología son fundamentales para readaptar los protocolos periódicamente.

Cuarta norma. «Lograr una respuesta rápida del laboratorio de microbiología»

El conocimiento de los patógenos causantes de una determinada infección o de su sensibilidad facilita el empleo de antibióticos de manera dirigida, y evita que los tratamientos empíricos de amplio espectro se mantengan muchos días o incluso hasta el final del tratamiento. Para esto, es necesario optimizar el traslado de muestras al laboratorio, la organización de su procesamiento y la difusión de sus resultados.
El manejo de las muestras debe seguir unas normas previamente establecidas, que incluyen la técnica de extracción u obtención de cada muestra, los medios de transporte y los tiempos mínimos en que deben llegar a los laboratorios para su procesamiento²⁵. El incumplimiento de alguna de ellas puede influir en la calidad de los resultados, ya que se aumenta el riesgo de contaminación y se facilita, en algunos casos, la multiplicación in situ, lo que distorsiona el resultado de estudios cuantitativos.
En los últimos años se han incorporado nuevas técnicas de diagnóstico rápido, basadas en el diagnóstico molecular (PCR en tiempo real)^26,27,28. Es aconsejable la incorporación progresiva de estos métodos de trabajo en los laboratorios de microbiología, ya que un diagnóstico etiológico precoz favorece la utilización de los antibióticos más adecuados y específicos.
La información obtenida en los laboratorios de microbiología, incluso los resultados de la técnica más sencilla (tinción de Gram), debe llegar con rapidez a los clínicos responsables del paciente. La comunicación mediante correo electrónico ha disminuido los tiempos de respuesta, pero este sistema no está disponible en todos los hospitales. El contacto telefónico para informar de aquellos resultados de mayor relevancia así como del aislamiento de patógenos multirresistentes (identificados como marcadores de multirresistencia) es la alternativa más sencilla y eficaz.
En algunos hospitales, los médicos intensivistas responsables de la vigilancia-control de infecciones relacionadas con la asistencia sanitaria participan diariamente en reuniones con el servicio de microbiología, lo que facilita el intercambio de información y el conocimiento de los cambios en los patrones de resistencia de la flora endógena de sus UCI.

Quinta norma. «Seleccionar un tratamiento dirigido cuando se conozca la etiología de la infección»

La información obtenida en los servicios de microbiología es la base del tratamiento dirigido. El aislamiento de uno o más microorganismos en alguna de las muestras de seguridad (sangre, LCR, líquido pleural, exudados purulentos obtenidos por punción, etc.) permite readaptar el tratamiento inicial. Siempre que sea posible, se deben escoger los antibióticos con el espectro de actividad más seguro y reducido, con evidencias contrastadas de su eficacia clínica y microbiológica, de su tolerabilidad así como de una mejor relación coste-beneficio.
En la mayoría de las infecciones en las que se conoce el patógeno causante de la infección, el tratamiento puede realizarse utilizando un solo antibiótico (monoterapia). En aquellos casos de microorganismos en los que es posible la aparición rápida de resistencias durante el tratamiento o en los que se ha documentado una proporción elevada de fracasos terapéuticos con monoterapia, se recomienda el empleo de 2 o más antimicrobianos²⁹. Cuando se aíslan 2 o más agentes patógenos en una misma muestra, debe valorarse la importancia de cada uno de los microorganismos identificados (alguno de ellos puede contaminar la muestra o proceder de una colonización). Si se acepta la etiología polimicrobiana en una determinada infección, se debe intentar una cobertura global con el mínimo número de antibióticos.

Sexta norma. «Monitorizar la eficacia del tratamiento»

La utilización de antibióticos no debe ser un acto sistemático que tranquiliza al médico, sino que debe acompañarse de un conjunto de medidas activas para vigilar la eficacia de estos. Se recomienda hacer la primera valoración de la respuesta terapéutica a las 72h de iniciado el tratamiento empírico. La aparición de nuevos signos de infección o el empeoramiento de los signos iniciales debe hacer sospechar que los antibióticos que se administran no son adecuados para tratar los agentes patógenos causantes de la infección. En este caso se repetirá la obtención de muestras de sangre y de los tejidos infectados y se procederá a la administración de antibióticos de rescate utilizando otros más potentes, de mayor espectro y con cobertura para patógenos potencialmente multirresistentes. En el caso contrario, en el que se observa una disminución de los signos iniciales, se continuará el tratamiento hasta la identificación de los patógenos y su sensibilidad, en cuyo caso se procede a su ajuste, tal como se ha indicado anteriormente.
En los casos en los que el tratamiento sea adecuado (según antibiograma) y la evolución no sea favorable, es necesario comprobar que los antibióticos que se administran tienen una buena penetración en los tejidos infectados, que se dan a las dosis adecuadas o que se dan con los intervalos necesarios para asegurar una relación farmacocinética/farmacodinámica (pK/pD) adecuada^30,31.
Para hacer la valoración del tratamiento se debe atender a la respuesta clínica y microbiológica, tanto al finalizar el tratamiento como en la visita de seguimiento, que puede oscilar entre 7–60 días dependiendo de la infección tratada.

Séptima norma. «Vigilar la aparición de efectos adversos o flora emergente multirresistente»

Cada familia de antibióticos se ha asociado con efectos adversos específicos. Muchos de estos son comunes a más de una familia de antibióticos y algunos se potencian con la utilización de otros productos farmacológicos, por lo que en la mayoría de las ocasiones es difícil atribuir a un fármaco un determinado efecto adverso.
Algunos de los efectos adversos más frecuentes (toxicidad renal, toxicidad ótica, selección de cepas mutantes resistentes) se relacionan con concentraciones plasmáticas inadecuadas de los antibióticos^32,33. Los pacientes críticos, en especial los quirúrgicos complicados, los quemados y los cardiópatas descompensados, presentan con frecuencia un importante aumento del volumen de distribución corporal, lo que influye en las concentraciones plasmáticas o tisulares alcanzadas. La inestabilidad hemodinámica y el fracaso renal condicionan, asimismo, la eliminación de los antibióticos. Estas características modifican el comportamiento farmacocinético de los antibióticos y justifican la amplia variabilidad interindividual en los niveles séricos obtenidos cuando se administran las mismas dosis. Por eso, es conveniente determinar las concentraciones plasmáticas de los antibióticos, en especial la de aquellos con un margen terapéutico pequeño (diferencia entre concentraciones tóxicas y concentraciones terapéuticas), como los aminoglucósidos y la vancomicina. La incorporación de programas de farmacocinética diseñados específicamente para la monitorización de estos fármacos permite ajustar su dosificación para obtener la máxima eficacia clínica con la mínima incidencia de efectos adversos³⁴.
El consumo de antibióticos en las UCI facilita la aparición de microorganismos patógenos multirresistentes, cuya presencia puede asociarse con fracaso del tratamiento administrado en un paciente concreto y con cambios en la política de antibióticos de esa UCI^35,36,37,38. Esto justifica la realización de vigilancia epidemiológica en los pacientes con utilización prolongada de antibióticos, que incluye la obtención de muestras en el foco de infección y en las mucosas (orofaringe, tráquea, heces).

Octava norma. «Limitar la duración del tratamiento en función de la respuesta clínica o microbiológica»

No existen indicaciones precisas sobre la duración del tratamiento de las infecciones en pacientes críticos. La respuesta clínica y microbiológica al tratamiento, la etiología de la infección y las características de los pacientes (inmunodepresión, prótesis, dispositivos intravasculares) son los principales factores para tener en cuenta al decidir la duración del tratamiento. La mayoría de las infecciones presentes en los pacientes críticos precisan de tratamiento antibiótico durante el tiempo necesario para que desaparezcan los signos y los síntomas clínicos más importantes de la infección, como son fiebre, leucocitosis, inestabilidad hemodinámica, intolerancia al aporte de glucosa y shunt pulmonar. A las 48–72h de controlarse estos síntomas puede retirarse el tratamiento antimicrobiano. La duración del tratamiento en pacientes no inmunodeprimidos con sepsis por bacilos gramnegativos oscila entre 8–14 días. Cuando las infecciones están producidas por patógenos multirresistentes, en los que existen evidencias de recidivas, como P. aeruginosa, Acinetobacter spp., S. aureus resistentes a meticilina o enterobacterias productoras de betalactamasas de espectro extendido, el tratamiento debe prolongarse por lo menos hasta las 2 semanas³⁹.
La persistencia de patógenos en la vía aérea de pacientes con traqueostomía o ventilación mecánica prolongada, en ausencia de signos clínicos de infección, no debe ser motivo de prolongación del tratamiento. Las infecciones urinarias relacionadas con sonda uretral producidas por bacilos gramnegativos y cocos grampositivos suelen responder, en la mayoría de los casos, a una semana de tratamiento. Cuando la evolución clínica y los estudios microbiológicos descartan la presencia de una infección o existe la evidencia de un diagnóstico alternativo, deben retirarse los antibióticos.

Novena norma. «Responsabilizar a un médico intensivista del control, la vigilancia y el tratamiento de las infecciones»

En las UCI, la figura del médico intensivista con dedicación parcial al control y el tratamiento de infecciones así como al control de la utilización de antibióticos ha supuesto un impulso en la consolidación de la política de antibióticos en estas áreas de alto riesgo. El paso previo para esto ha sido reconocer que uno de los objetivos de cualquier servicio, incluida la UCI, es monitorizar la morbilidad que se genera con su actividad. Entre los indicadores de calidad de un servicio, reconocidos por los diferentes responsables de la sanidad pública, se incluye el conocimiento de la evolución de las infecciones relacionadas con la asistencia sanitaria así como del uso y el consumo de antibióticos.
Las funciones del médico intensivista especializado en el tratamiento de pacientes críticos con infecciones graves son las siguientes:

·                                 1) Conocer y dar a conocer la información obtenida con los sistemas de vigilancia de infección relacionada con la asistencia sanitaria. En colaboración con otros profesionales del hospital, debe participar en los estudios (prevalencia o incidencia) de vigilancia de infección relacionada con la asistencia sanitaria del hospital, pero es el responsable del seguimiento de los enfermos ingresados en UCI. La información de este servicio debe transmitirse de forma regular al comité de infecciones y a la dirección médica o asistencial del hospital pero, al mismo tiempo, debe comunicarse al resto del personal sanitario de la UCI.

·                                 2) Mantener relaciones fluidas con los servicios de microbiología y de farmacia. Si la estructura del hospital lo permite, debe participar en las reuniones del servicio de microbiología, en donde se comentan los aislamientos más significativos del hospital. En colaboración con este servicio, debe elaborar el mapa epidemiológico de la UCI en donde se informa no solo de las tasas de las principales infecciones, sino de la evolución de los principales marcadores de multirresistencia y de los patrones de sensibilidad de los agentes patógenos más frecuentes en cada medio. En colaboración con el servicio de farmacología, debe controlar la utilización de los antimicrobianos, tanto en lo que se refiere a indicaciones como a dosis y a duración del tratamiento. Es el interlocutor con estos servicios en las 2 direcciones: informa de la situación de pacientes de riesgo y recibe los datos de mayor interés con la mayor rapidez.

·                                 3) Proponer al personal de la UCI la implantación de protocolos terapéuticos y preventivos para las infecciones más frecuentes. Para esto, debe presentar en el propio servicio los protocolos terapéuticos o de prevención que se elaboran en el hospital, así como aquellos protocolos específicos de la UCI (prevención de la neumonía en pacientes ventilados y de las infecciones relacionadas con catéteres, entre otros). Siempre que sea posible, debe organizarse un grupo de trabajo en el que colaboren otros profesionales sanitarios de la UCI (enfermería, auxiliares) con la intención de colaborar conjuntamente en la recogida de información, en el control de la aplicación de los diferentes protocolos y en la revisión periódica de las técnicas y procedimientos realizados por enfermería.

Décima norma. «Corresponsabilizar a todo el personal sanitario del adecuado cumplimiento de las normas»

El cumplimiento de las normas de política de antibióticos es responsabilidad de todo el personal médico que trabaja o atiende pacientes en UCI. La realización de reuniones periódicas en las que se presenten los indicadores de consumo de antibióticos así como la evolución de las tasas de infección y de los patrones de sensibilidad de los patógenos más frecuentes permite la revisión de los protocolos de actuación y corresponsabilizar a todos los médicos para su cumplimiento. La realización de controles y auditorías en las que se investiga el cumplimiento de un determinado protocolo asistencial permite conocer el grado de seguimiento de las normas de política de antibióticos en un determinado servicio y por unos determinados profesionales.

Estrategias generales del uso de antibióticos en pacientes críticos

Con la finalidad de optimizar el uso de antibióticos en el entorno de los pacientes críticos se han propuesto diversas estrategias. Entre ellas destacan la desescalada terapéutica (de-escalation therapy), el ciclado de antibiótico (antibiotic cycling), el tratamiento anticipado (preemptive therapy) y la aplicación de parámetros pK/pD para ajustar la dosificación.

·                                 1) Desescalada terapéutica (de-escalation therapy). Consiste en la administración inicial de un amplio tratamiento empírico con la intención de cubrir los patógenos más frecuentemente relacionados con la infección por tratar, incluidos los patógenos multirresistentes, seguido de un ajuste rápido del tratamiento antibiótico una vez conocido el agente etiológico⁴⁰. El ajuste debe realizarse entre el segundo y tercer día de la instauración del tratamiento antibiótico inicial. La aplicabilidad de esta estrategia se ha evaluado principalmente en pacientes críticos con neumonía nosocomial o shock séptico^41,42,

 PRESENTADOS EN CONGRESO CALILAB 

Noviembre - 2010                Bs As - Argentina

_________________________________________________________________________________

TRABAJO 1 

ES NECESARIO TUBO CON GEL PARA LA DETERMINACION DE POTASIO EN SUERO ?

C.Rodríguez, C. Anile,  A. Furci, G. Jiménez, M. Jiménez, R. De Miguel

El potasio catión intracelular por excelencia cumple un rol imprescindible en la trasmision del impulso neuro-muscular . Sus alteraciones pueden afectar la contractibilidad muscular y de esa manera condicionar la funcion miocardica y la vida del paciente.
Se sabe que el proceso de coagulación genera lisis de glóbulos rojos y la liberación del Potasio intracelular.
El objetivo del estudio es verificar si el contacto del suero con el coagulo  afecta la concentración de Potasio en suero, para ello se comparan los resultados de Potasio obtenidos con vacutaneir donde el gel separa el suero de los glóbulos con los resultados de Potasio obtenidos con un tubo común donde el suero esta en contacto con el coagulo. Se realiza la evaluación en de un  tiempo corto, lógico y probable en el procesamiento de la muestra y en caso que el valor se vea afectado dimensionar la magnitud del cambio.
Se midio el K en suero en 560 pacientes de los cuales 369 fueron procesados en tubo comun y 191 en vacutainer.
Las muestras se midieron a tiempo 0 con un autoanalizador de química Beckman LX20 y se repitió la medición, 150 min ± 30 min después, en un analizador de gases multiparemetrico Rapilab 1265. La metodología de medición en ambos instrumentos fue electrodo especifico, en LX20 con medición  indirecta, en Rapilab 1250 medición directa.

RESULTADOS

 Comparamos las distribuciones de las mediciones obtenidas en cada uno de los tubos.
Se utiliza el test de bondad de ajuste  Kolmorof- Smirnov para dos muestras. Las distribuciones  resultaron ser iguales, con lo cual resulta lo mismo medir potasio en tubo común y en tubo vacutainer

CONCLUSIONES          

• - De acuerdo a los resultados obtenidos no se observan diferencias en los dosajes de potasio usando tubo vacutainer o tubo comun como contenedor de la sangre
• - En el caso de LX20 obtenemos un p-valor de 0.2273 y para el caso de Rapilab 1265 un p-valor de 0.2176, por lo tanto las dos distribuciones son las mismas. NO existen alteraciones en la concentración de Potasio en suero con demoras en procesamiento del orden de 150 minutos ± 30 minutos
• - No existen diferencias de consideración midiendo con metodologia de electrodos específicos directa o indirecta

___________________________________________________________________________

TRABAJO 2 

POTASIO EN SUERO O POTASIO EN SANGRE ENTERA ..... ES LO MISMO ?

C.Rodríguez, C. Anile,  A. Furci, G. Jiménez, J. Oyhamburu, R. De Miguel

El potasio catión intracelular por excelencia cumple un rol imprescindible en la trasmision del impulso neuro-muscularpar. Sus alteraciones pueden afectar la contractibilidad muscular y de esa manera condicionar la funcion miocardica y la vida del paciente.
El avance tecnologico de los ultimos lustros ha permitido que el  laboratorio pueda realizar la deteminación de Potasio en suero o sangre entera. Si bien son dos alternativas de muestras posibles existe entre ambas una diferencia sustancial ya que para la obtención del suero ha habido previamente un proceso de coagulación mientras que la muestra de sangre entera esta libre de esa posibilidad. Se sabe que el proceso de coagulación genera lisis de glóbulos rojos y la liberación del Potasio intracelular
El objetivo de este trabajo es verificar si existe diferencias en los valores de Potasio en suero y sangre entera y si la hay cuantificar la misma.

MATERIALES Y METODOS

Se procesaron 560 muestras de diferentes pacientes, de cada uno se analizaron simultáneamente  2 tipos de muestra:

-    Sangre entera, tomada con jeringa preparada con heparina diluida 1/7.

-    Suero, obtenidos 369 usando como contenedor de la sangre tubo comun y 191

      utilizando tubo vacutainer.

Las muestras se midieron con una diferencia de tiempo no mayor de 60 minutos.
Ambos tipo de muestra, suero  y de sangre entera, se midieron en un analizador de gases multiparemetrico Rapilab 1265. .
La metodología de medición fue electrodo especifico con medición directa e indirecta respectivamente.
Se evaluo la existencia de hemolisis por medición de hemoglobina libre, descartandose  las muestras con valores superiores a 1.5 gr/L. El dopaje de Hemoglobina libre se realizó en una analizador de quimica Beckman LX 20

RESULTADOS.

Se obtuvieron los siguientes resultados:

             - Potasio en suero:                    Media de 4.19 mmol/L
                                                             Mediana de 4.10 mmol/L

            - Potasio en sangre:                  Media de 3.74 mmol/L
                                                            Mediana de 3.70 mmol/L. 

* Mediante el test de bondad de ajuste de Kolmorogov para dos muestras (suero y sangre), obtenemos un p -valor 6.6393x10-18. Podemos afirmar que las dos distribuciones son distintas. También  realizamos un test para muestras apareadas y el p-valor es 1.3494x10-176, con lo que se concluye que las mediciones realizadas la media en suero es superior a las de sangre entera y la diferencia es significativa.

* La distribución acumulada (fda) para las dos variables, evidencia que mediciones en suero  son siempre superiores a las realizadas en sangre entera.

* Con el objetivo de cuantificar las diferencias entre las dos medias construimos un intervalo de confianza de nivel 95%, para la diferencia de medias. Si llamamos μ_u al valor medio de la media en suero y μ_a   al valor medio de la media en sangre, tenemos con μ_a - μ_u  con probabilidad de 0.95 se encuentra entre 0.42 y 0.46. Esta es una forma global de cuantificar la diferencia entre ambas mediciones. Ello implica que si se mide el valor del potasio en sangre puedo suponer con probabilidad alta que el valor del potasio en suero va a estar entre ese valor medido más 0.42 y  ese valor medido más 0.46.

* Se cuantificaron las diferencias entre el Potasio medido en suero y el medido en sangre para diferentes bandas forzadas de valores de Potasio. 

Los resultados fueron:;

• - Potasio menor de 3.0 mEq/L

                        - Percentilo 05 % de la diferencia:          0.135 mEq/L
                        - Percentilo 50%  de la diferencia           0.300 mEq/L
                        - Percentilo 95%  de la diferencia       0.580 mEq/L

• - Potasio entre 3.1 y 4.0 3.0 Meq/L

                        - Percentilo 05 % de la diferencia           0.100 mEq/L
                        - Percentilo 50% de la diferencia            0.350 mEq/L
                        - Percentilo 95% de la diferencia        0.722 mEq/L

• - Potasio entre 4.1 y 5.0 Meq/L

                        - Percentilo 05 % de la diferencia:          0.200 mEq/
                        - Percentilo 50% de la diferencia            0.450 mEq/L
                        - Percentilo 95% de la diferencia        0.850 mEq/L 

• - Potasio mayor de 5.0 Meq/L

                        - Percentilo 05 % de la diferencia:          0.117 mEq/L
                        - Percentilo 50%  de la diferencia           0.550 mEq/L
                        - Percentilo 95%  de la diferencia       1.050 mEq/L

CONCLUSIONES

• Los resultados muestran que los Potasio en suero y sangre entera son de magnitudes diferentes y las diferencias son estadisticamente significativas
• Con un intervalo de confianza del nivel 95 % los Potasios en suero resultan entre 0.42 mEq/L y 0.46 mEq/L mas elevados que los valores de sangre entera
• Es de resaltar que en algunas muestras los valores de las diferencias de entre los Potasio de suero y sangre entera son clinicamente muy importantes (percentilo 95)
• En un monitoreo continuo de los niveles de Potasio en un paciente es necesario utilizar siempre el mismo tipo de muestra
• Los resultados muestran que a medida que aumenta el valor de potasio aumenta la diferencia entre el K medido en suero y en sangre entera

Valor diagnóstico de la procalcitonina, la interleucina 8, la interleucina 6 y la proteína C reactiva en la detección de bacteriemia y fungemia en pacientes con cáncer

                        Eduardo Aznar-Oroval, Marina Sánchez-Yepes,  Pablo Lorente-Alegre, Mari Carmen San Juan-Gadea, Blanca Ortiz-Muñoz, Pilar Pérez-Ballestero, Isabel Picón-Roig, Joaquín Maíquez-Richart

                                                                      Enferm Infecc Microbiol Clin. 2010;28:273-7.

Introducción y objetivo

La bacteriemia es una de las causas más importantes de morbimortalidad en los pacientes con cáncer.
El objetivo del presente estudio es evaluar la utilidad diagnóstica de la procalcitonina (PCT), la interleucina 8 (IL-8), la interleucina 6 (IL-6) y la proteína C reactiva (PCR) en la detección de bacteriemia en pacientes con cáncer.

Introduction

La bacteriemia en pacientes con cáncer es una situación de extrema gravedad.
La mortalidad alcanza el 32% de los casos y su incidencia en episodios de neutropenia postquimioterapia está próxima al 24%.
Los focos más frecuentes de bacteriemia se encuentran en el tracto genitourinario, el tracto respiratorio, las heridas quirúrgicas, el tracto digestivo y los dispositivos intravasculares, aunque en un 25% de los casos el foco originario es desconocido^1,2.
La etiología de las bacteriemias de adquisición nosocomial muestra un predominio de bacterias grampositivas (65%) sobre gramnegativas (25%), mientras que las bacterias anaerobias estrictas permanecen estables (3%) y los hongos alcanzan en algunas series hasta el 9% de los aislamientos.
En las bacteriemias de origen comunitario, el predominio es de gramnegativas, al igual que en las bacteriemias asociadas a cuidados sanitarios (68 y 64%, respectivamente)^3,4,5.
La detección precoz de una infección bacteriana es de vital importancia en el paciente con cáncer, sobre todo si está recibiendo algún régimen de quimioterapia citotóxica.
Es conocido desde hace varias décadas que la intensidad y la duración de la neutropenia es un factor determinante en la aparición de infecciones⁶.
Otros factores que contribuyen al desarrollo de procesos infecciosos son la enfermedad tumoral de base, la existencia de comorbilidad asociada, el empleo de procedimientos medicoquirúrgicos invasivos y el progresivo incremento de resistencias bacterianas a los antimicrobianos^7,8.
En este sentido, sería de gran utilidad contar con indicadores sensibles y específicos que nos permitieran diferenciar pacientes con bacteriemia de aquellos que no la presentan.
Entre los marcadores más utilizados en la práctica clínica se encuentran:
• La procalcitonina (PCT), péptido sintetizado en condiciones normales por las células C de la glándula tiroides y transformado rápidamente en calcitonina, sus niveles en sangre son muy bajos.
En las infecciones, la PCT es capaz de sintetizarse en tejidos extratiroideos y sus niveles en sangre aumentan, como se demuestra tras la administración intravenosa de endotoxina bacteriana⁹.
 • La interleucina 6 (IL-6) y la interleucina (IL-8) son unas de las más importantes citocinas asociadas con la sepsis.
  Los macrófagos, los monocitos, los linfocitos y las células endoteliales las liberan en respuesta a un estímulo inflamatorio¹⁰.
  La IL-6 es una citocina multifuncional reguladora de las funciones de los linfocitos B y T y de la producción de la proteína C reactiva (PCR) como reactante de fase aguda¹¹.
  La IL-8 es una citocina inflamatoria con capacidad de activar los neutrófilos y aumentar su quimiotaxis¹².
• La PCR se sintetiza en los hepatocitos como proteína de fase aguda que aumenta en procesos inflamatorios, infecciones, traumatismos, quemaduras, infartos tisulares y neoplasias¹³.

Pacientes y métodos

Se midieron los valores de PCT, IL-8, IL-6 y PCR en 2 grupos de pacientes con cáncer que presentaron fiebre: el grupo con bacteriemia verdadera y el grupo sin bacteriemia.

Resultados

Se estudiaron 79 síndromes febriles en 79 pacientes, 43 hombres y 36 mujeres. Cuarenta y cuatro pacientes pertenecían al grupo de bacteriemia verdadera.
Se encontraron diferencias significativas al comparar los valores de PCT, IL-8 e IL-6 (p<0,001, p<0,001, p=0,002, respectivamente) entre los pacientes con bacteriemia verdadera y sin bacteriemia.
Los resultados de la PCR no mostraron diferencias significativas entre los 2 grupos estudiados (p=0,23).
El punto de corte para la PCT fue de 0,5ng/ml y mostró la mejor especificidad (91,4%), con una sensibilidad del 59,1%.

CONCLUSION

El marcador de infección que puede aportar más información en el diagnóstico de bacteriemia en pacientes con cáncer es la PCT.

Ud. Puede consultar el trabajo completo en:

Enferm Infecc Microbiol Clin. 2010;28:273-7.

Nuevos biomarcadores en la insuficiencia cardiaca: aplicaciones en el diagnóstico, pronóstico y pautas de tratamiento

                                                                                  A. Mark Richards

                                                                                   Rev Esp Cardiol.2010; 63 :635-9

Los biomarcadores son variables biológicas que aportan información sobre enfermedades concretas. En la insuficiencia cardiaca (IC), ésta puede consistir en características demográficas (edad y sexo), imagen cardiaca (ecocardiografía, radiografía, gammagrafía o resonancia magnética) o incluso la determinación de un polimorfismo genético específico. Sin embargo, generalmente se usa el término biomarcador para referirse a sustancias circulantes que pueden determinarse mediante análisis que quedan fuera de las pruebas estándar de bioquímica y hematología usadas en el manejo clínico habitual. Existe un conjunto cada vez más amplio de sustancias bioquímicas circulantes que reflejan distintos aspectos de la fisiopatología de la IC.

Los biomarcadores clave en la IC que se aplican en la práctica clínica habitual son los péptidos natriuréticos tipo B (BNP y NT-proBNP). Estas sustancias ilustran lo que los biomarcadores pueden aportar en la IC y muestran también algunos de los inconvenientes que presentan respecto a lo que sería un marcador ideal.

Criterios para la aplicación clínica de biomarcadores

En revisiones recientes^1,2 se han definido los criterios para valorar la utilidad clínica de los biomarcadores. El primero y más importante es que la determinación debe facilitar el manejo clínico y mejorar el pronóstico de los pacientes de una o más de las siguientes formas. Comparados con las pruebas existentes hasta el momento, los nuevos marcadores pueden mejorar la certeza diagnóstica. Las concentraciones del marcador pueden asociarse al riesgo de aparición o agravamiento de la IC (lo ideal es que conlleve una respuesta con un tratamiento específico). La monitorización a través de determinaciones seriadas de marcadores debe mejorar los resultados obtenidos en las variables de valoración (es decir, reducción de la descompensación aguda, reducción de la mortalidad o mejora de la calidad de vida).

En segundo lugar, el marcador debe aportar una información de la que no se pueda disponer de otro modo. Debe haber una relación clara entre la cantidad del marcador y el diagnóstico o el pronóstico. El marcador debe mejorar la certeza diagnóstica o la estratificación del riesgo clínico respecto a lo alcanzado con las pruebas ya existentes.

Por último, las cuestiones prácticas, técnicas y comerciales son pertinentes siempre. Los métodos de análisis deben ser exactos y reproducibles y estar bien fundamentados. El producto analizado en el suero o el plasma debe ser lo suficientemente estable para evitar una degradación excesiva tras la obtención de la muestra. La prueba analítica utilizada debe estar disponible y tener un coste aceptable.

De entre la multitud de biomarcadores candidatos investigados actualmente en la IC, son pocos los que llegarán a satisfacer estos criterios. Además del rendimiento exigido a la prueba, la aplicabilidad práctica y las limitaciones presupuestarias harán que los marcadores que lleguen a establecerse en el manejo clínico de la IC sean escasos. Esto no niega la importancia de la perspectiva fisiopatológica proporcionada por la investigación de muchos biomarcadores en la IC. Los biomarcadores reflejan uno o varios de los aspectos del complejo síndrome de la IC. Pueden aportar información relativa a la etiología del trastorno y —puesto que reflejan procesos patológicos que se producen en los medios subcelular, celular, del órgano o de todo el organismo— pueden identificar nuevos agentes terapéuticos.

Clasificación de los biomarcadores en la IC

Los biomarcadores de interés en la IC pueden agruparse de forma general según el conocimiento actual de su papel en la fisiopatología del trastorno (tabla 1). El subgrupo mejor conocido es el de las neurohormonas, que incluye los péptidos natriuréticos (PN) cardiacos, los componentes del sistema renina-angiotensina-aldosterona (SRAA), las catecolaminas, la arginina-vasopresina y los péptidos vasoactivos derivados del endotelio, como endotelina, adrenomedulina y urocortinas. Estas sustancias endocrinas, paracrinas o autocrinas, biológicamente activas, reflejan la respuesta sistémica o cardiaca a la lesión cardiaca aguda o crónica. Algunas de ellas tienen un carácter predominantemente compensatorio. Los PN facilitan el filtrado glomerular y la excreción de sodio, al tiempo que inhiben la vasoconstricción/retención de sodio del SRAA y ejercen un efecto tónico antitrófico que atenúa la fibrosis intersticial y la hipertrofia cardiaca.

Los animales modificados genéticamente mediante la deleción de ANP, BNP o sus receptores específicos son hipertensos y presentan hipertrofia y fibrosis cardiacas, con aumento de la mortalidad. El estímulo secretor clave para el PN es la distensión de los miocardiocitos y el aumento de las presiones intracardiacas que caracterizan el desencadenante de la secreción de PN en la IC. Este mecanismo subyace a la relación entre las concentraciones plasmáticas de PNB y el diagnóstico de IC descompensada, la gravedad de la anomalía estructural y funcional cardiaca y el pronóstico³. Los siguientes factores modifican la relación: edad, sexo, función renal, masa corporal, hipoxemia, arritmias, estado suprarrenal y tiroideo, inflamación y enfermedad multisistémica grave.

El deterioro cardiaco con reducciones asociadas del flujo sanguíneo regional y el aumento del impulso simpático renal, cardiaco y sistémico estimulan el SRAA, lo que constituye una respuesta mal adaptada «destinada» a mantener la presión arterial y la perfusión de los órganos vitales. El PN contrarresta este sistema y su activación induce vasoconstricción sistémica y retención de sodio, hipertrofia cardiaca y fibrosis intersticial. Junto con la actividad del sistema nervioso simpático y las concentraciones elevadas de catecolaminas circulantes, parece que el SRAA es un factor importante en el fomento de un remodelado ventricular adverso tras la lesión cardiaca y facilitaría la instauración del círculo vicioso de disfunción cardiaca que aumenta en espiral, con descompensación y mortalidad alta, que se observa en la IC. Las concentraciones plasmáticas de catecolaminas, la actividad de renina en plasma y la aldosterona están relacionadas con el pronóstico de la IC⁴.

La arginina-vasopresina se activa en la IC y pasa a ser regulada por parámetros hemodinámicos y por la angiotensina II, en vez de por la osmolaridad plasmática, cuando progresa la IC. Esto puede conducir a una antidiuresis inadecuada (con posible hiponatremia) y vasoconstricción periférica. La endotelina, un potente péptido vasoconstrictor endotelial, está elevada, lo que se asocia a un mal pronóstico en la IC. El bloqueo agudo de la endotelina en la IC reduce la presión arterial pulmonar y la presión de llenado ventricular y aumenta el gasto cardiaco⁵.

En cambio, la adrenomedulina (ADM), que también está elevada en la IC, con unos valores relacionados con el pronóstico, es un péptido vasodilatador de origen endotelial. En la IC experimental, la infusión de ADM se asocia a un perfil hemodinámico beneficioso. Activa la renina sin elevar las concentraciones de aldosterona y reduce las concentraciones de PN en paralelo con reducciones de las presiones auriculares izquierdas⁶.

Las concentraciones plasmáticas de urocortinas (que forman parte de la familia de los péptidos factores liberadores de corticotropina) están aumentadas en la IC. En la IC experimental, las urocortinas I, II y III inducen reducciones importantes de las presiones de llenado del corazón derecho y del ventrículo izquierdo, aumentos considerables del gasto cardiaco y una reducción del trabajo cardiaco junto con una supresión del SRAA, la endotelina y la arginina-vasopresina, y una mejoría notable de la filtración renal. El bloqueo de la urocortina exacerba las manifestaciones hemodinámicas, renales y neurohormonales de la IC experimental, lo que indica que la urocortina endógena es un factor importante que contribuye beneficiosamente en la respuesta compensatoria a la IC⁷.

Los marcadores de la inflamación y el estrés oxidativo son otro grupo de biomarcadores de la IC. La proteína C reactiva (PCR), el factor de necrosis tumoral alfa (FNTα) y otras citocinas están aumentadas en la IC y las concentraciones elevadas son un indicador de peor pronóstico^1,8,9. La actividad de la mieloperoxidasa, los isoprostanos en orina y plasma y otros marcadores de la lesión oxidativa aumentan también a medida que se incrementa la gravedad de la IC. Las alteraciones de la PCR en la enfermedad cardiovascular se conocen desde hace tiempo, mientras que las relaciones entre las citocinas y el riesgo de IC (y con el pronóstico en la IC conocida) se identificaron en los años noventa. Estas respuestas del sistema inmunitario pueden tener efectos nocivos a través de la estimulación de factores adversos neurohormonales como la endotelina 1, además de un fomento más directo de la necrosis y la apoptosis de los miocardiocitos.

El remodelado ventricular adverso (causado en parte por los efectos cardiotóxicos de la activación de neurohormonas y citocinas) evoluciona de manera paralela a los marcadores de degradación y formación de la matriz intersticial. Entre estos marcadores se encuentran las concentraciones circulantes de metaloproteinasas de matriz, los inhibidores tisulares de metaloproteinasas y los procolágenos¹⁰. El FNTα puede causar dilatación cardiaca, en parte a través de un aumento de la expresión y la actividad de las metaloproteinasas, lo cual ilustra nuevamente la compleja interrelación entre los diferentes elementos de las respuestas moleculares al deterioro cardiaco. La apoptosis y la necrosis de los miocardiocitos se reflejan en los marcadores de la lesión miocitaria, incluidas las troponinas I y T. Mejor conocidas por su papel en el diagnóstico y tratamiento de los síndromes coronarios agudos, las concentraciones de troponinas tienen un claro valor pronóstico en la IC y el desarrollo de pruebas analíticas cada vez más sensibles facilitará su uso más amplio en esta afección para estratificar el riesgo¹¹.

Continúan apareciendo nuevos marcadores derivados de aspectos diversos de la fisiopatología de la IC. El ST2 es una forma soluble del receptor de la interleucina 33 inducido mediante la distensión de los miocardiocitos. La interleucina 33 interviene en una vía antifibrótica en el corazón¹². La coenzima Q10 está reducida en la IC, y posiblemente refleja un deterioro fundamental de la respiración mitocondrial. Otros marcadores de reciente identificación son el factor de diferenciación del crecimiento 15, la osteoprotegerina, la adiponectina, la galectina 3 y la urotensina II^13-15.

De esta amplia gama de sustancias, hasta el momento sólo los péptidos de tipo B se han establecido como análisis útiles recomendados en el diagnóstico de la IC aguda^1,2. Su valor pronóstico independiente en todo el espectro clínico, que va del factor de riesgo a la IC en fase terminal, está bien establecido. Las determinaciones seriadas permiten mejorar el tratamiento de la IC tanto aguda como crónica. Los ensayos terapéuticos incluyen ahora un valor umbral del BNP como criterio de inclusión habitual.

Los valores del propéptido natriurético auricular de región media tienen una potencia diagnóstica para la IC aguda similar a la de los BNP. Los valores de proadrenomedulina de región media y de ST2 son iguales o superiores a los péptidos de tipo B como indicadores del pronóstico en la IC aguda. Está por verse si uno o varios de estos biomarcadores podrán sustituir a los BNP o se utilizarán en combinación con ellos.

Los péptidos de tipo B son los únicos biomarcadores realmente establecidos en la práctica clínica en la IC. El papel etiológico clave del SRAA y el sistema nervioso simpático en la progresión de la IC son claros, pero no se ha observado beneficio alguno con la determinación sistemática de la renina, la angiotensina II, la aldosterona o las catecolaminas plasmáticas para el diagnóstico, en la introducción del tratamiento o el seguimiento de la IC.

Los biomarcadores pueden ser útiles en la selección de casos para determinados tratamientos¹. Los subestudios realizados en los ensayos controlados y aleatorizados de los inhibidores de la enzima de conversión de angiotensina (IECA) indican que el máximo beneficio relativo se obtiene cuando la actividad de SRAA basal es elevada. En el ensayo RALES, que evaluó el empleo de espironolactona en la IC grave, el efecto beneficioso quedó limitado a los pacientes con los valores plasmáticos del procolágeno 3 más elevados^1,2. Algunas evidencias obtenidas en ensayos controlados y aleatorizados indican que la mayor elevación de los BNP identifica a los pacientes que obtienen beneficio con la introducción de carvedilol¹. En la actualidad, las dosis para el tratamiento de la IC se basan en el enfoque de «una misma talla para todos», derivado de los resultados de ensayos controlados y aleatorizados. Sin embargo, cabe pensar que en el futuro los tratamientos estarán sujetos a una prescripción más específica según las determinaciones de los biomarcadores.

Identificación de dianas terapéuticas mediante biomarcadores

El conocimiento del papel de los sistemas neurohormonales en la evolución de la IC ha sido el fundamento de los avances terapéuticos desde mediados de los años ochenta. Esto se ha basado en el estudio de las concentraciones circulantes de biomarcadores^1,2. El bloqueo del SRAA con el empleo de IECA, antagonistas de los receptores de angiotensina II y antagonistas de la aldosterona se sustenta en el conocimiento adquirido sobre los efectos adversos de este sistema en la evolución de la IC. El bloqueo beta es otro tratamiento eficaz cuyo fundamento lógico está en el conocimiento de los efectos de un estado adrenérgico inadecuado y de las catecolaminas circulantes en el balance energético cardiaco, la resistencia vascular periférica, la integridad celular y la secreción de renina en la IC. El BNP recombinante humano (neseritida) se ha introducido como tratamiento de la IC aguda descompensada. Quedan cuestiones por resolver respecto a sus efectos en la función renal y la mortalidad, pero parece claro que la neseritida reduce las presiones de llenado cardiaco y alivia la disnea en la IC aguda.

El abordaje lógico de dianas neurohormonales no siempre ha tenido éxito. En la última década, los tratamientos experimentales basados en una lógica impecable (a menudo con una evidencia preclínica convincente) no han logrado reducir la morbimortalidad en la IC^1,2. Los fármacos que reducen la emisión de impulsos simpáticos centrales, los bloqueadores del FNTα y los antagonistas de la endotelina no han resultado útiles. Los antagonistas de la arginina-vasopresina no han reducido la mortalidad. Está por estudiar si la manipulación de las concentraciones plasmáticas o tisulares de urocortina o adrenomedulina, el bloqueo de mediadores específicos de la inflamación/oxidación o la formación de enlaces cruzados del colágeno intersticial resultan útiles en la IC. Solamente el empleo de ensayos controlados, aleatorizados y de diseño riguroso permitirá responder a estas preguntas.

Multimarcadores

La combinación de dos o más biomarcadores circulantes que reflejan aspectos diferentes de la fisiopatología de la IC y tienen relación independiente con el resultado clínico puede mejorar la capacidad pronóstica. En una evaluación reciente de las concentraciones de NT-proBNP y ST2 en pacientes con IC aguda que acudieron al servicio de urgencias, se observó que la elevación simultánea de ambos biomarcadores comportaba un riesgo de mortalidad muy superior al asociado a la elevación de uno solo de ellos¹². La combinación de marcadores que reflejan predominantemente las respuestas de fase aguda frente a la lesión cardiaca con marcadores de la carga hemodinámica (distensión de los miocardiocitos) puede ser especialmente útil, puesto que podría aclarar el carácter agudo, la gravedad y el pronóstico.

Resumen

Serán pocos los biomarcadores candidatos que cumplan los criterios exigidos para una aplicación generalizada en el manejo clínico de la IC. Estos criterios son: a) análisis accesibles, estandarizados y de coste aceptable, que puedan tener una aplicación de alto volumen y una rápida rotación; b) asociación consistente de sus valores con el diagnóstico y el pronóstico en la IC, y c) facilitación de una mejora de los resultados clínicos en la IC.

La combinación de marcadores puede aportar una información que compense las limitaciones de cada prueba individual. Los nuevos marcadores pueden apuntar o no a nuevas dianas terapéuticas. Sin embargo, cada nuevo biomarcador aportará una perspectiva adicional respecto a la fisiopatología de la IC. Por el momento, los criterios de utilidad clínica se han cumplido únicamente para los BNP. Han transcurrido 20 años desde que se descubriera el BNP con la identificación casi inmediata de la asociación entre las concentraciones plasmáticas circulantes de BNP y el grado de disfunción cardiaca. Tras ello aparecieron miles de publicaciones relativas a la ciencia básica y a los aspectos clínicos de los péptidos de tipo B, antes de llegar a su actual aceptación y aplicación clínica. Esto es un indicador de la carga de evidencia necesaria para futuros biomarcadores candidatos. Por fortuna, el camino que va del descubrimiento a la prueba de la utilidad clínica está bien establecido gracias, en gran parte, al esfuerzo mundial realizado en la investigación de los PN. La experiencia de investigación básica y clínica acumulada (incluidos los bancos existentes de muestras procedentes de cohortes de pacientes bien caracterizados) deberá facilitar una evaluación más eficiente de los nuevos biomarcadores candidatos. La exploración continua del genoma, junto con el avance de las disciplinas de la proteómica y la metabolómica, no hace prever escasez de nuevas moléculas de biomarcadores candidatas en el futuro²

Bibliografía

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Bench-to-bedside review: Significance and interpretation of elevated troponin in septic patients

                                                                                  Raphael Favory and Remi Neviere
                                                                                  Crit Care. 2006; 10(4): 224. - Review

Abstract

Because no bedside method is currently available to evaluate myocardial contractility independent of loading conditions, a biological marker that could detect myocardial dysfunction in the early stage of severe sepsis would be a helpful tool in the management of septic patients. Clinical and experimental studies have reported that plasma cardiac troponin levels are increased in sepsis and could indicate myocardial dysfunction and poor outcome. The high prevalence of elevated levels of cardiac troponins in sepsis raises the question of what mechanism results in their release into the circulation. Apart from focal ischemia, several factors may contribute to the microinjury and minimal myocardial cell damage in the setting of septic shock. A possible direct cardiac myocytotoxic effect of endotoxins, cytokines or reactive oxygen radicals induced by the infectious process and produced by activated neutrophils, macrophages and endothelial cells has been postulated. The presence of microvascular failure and regional wall motion abnormalities, which are frequently observed in positive-troponin patients, also suggest ventricular wall strain and cardiac cell necrosis. Altogether, the available studies support the contention that cardiac troponin release is a valuable marker of myocardial injury in patients with septic shock.

Introduction

In 2000, the Joint European Society of Cardiology/American College of Cardiology Committee proposed a new definition of myocardial infarction based predominantly on the detection of the cardiospecific biomarkers troponin T and troponin I in the appropriate clinical setting [1]. Given that cardiac troponin is highly sensitive for detecting even minimal myocardial-cell necrosis, these markers may become 'positive' even in the absence of thrombotic acute coronary syndromes [2]. This may occasionally be related to a spurious troponin elevation but may also be due to several non-thrombotic cardiac and systemic diseases [2-4]. Sepsis and other systemic inflammatory processes may lead to myocardial depression and cellular injury, greatly increased oxygen consumption, reduced microvascular circulation, and decreased oxygen delivery to the heart, ultimately resulting in the release of troponin into the systemic circulation [5]. The aim of this review is to go from bench to bedside to determine what evidence and interests are able to incite intensivists to evaluate the cardiac troponin plasma marker in the context of sepsis.

Limitations in cardiac assessment at the bedside

Abnormalities of cardiac function are frequent in patients with sepsis. Approximately 50% of patients with severe sepsis and septic shock may develop impairment of ventricular performance. Whereas evaluation of myocardial performance during septic shock is of critical importance to select the best therapeutic options, several factors complicate the diagnosis of sepsis-induced myocardial dysfunction in humans. Making accurate measurements of cardiac function is difficult and this is confounded by the inherent difficulty of excluding patients with true coronary insufficiency with sepsis. The available evaluation methods have their strengths and limitations, leading to an absence of consensus regarding the gold standard technique to assess cardiac function. In addition, most of the contractility indexes are affected by peripheral vasodilatation and changes in loading conditions observed in septic shock. In addition, catecholamine stress observed in sepsis stimulates the myocardium and may, therefore, mask myocardial depression. Since alteration of myocardial performance in sepsis may be related to structural abnormalities of the heart, biochemical markers could thus be useful in the diagnosis of sepsis-induced myocardial dysfunction. Recently, plasma cardiac troponin has been proposed as a biomarker that accurately detects myocardial dysfunction and provides prognosis information in septic patients.

What are troponins?

Cardiac troponins are regulatory proteins that control the calcium-mediated interaction of actin and myosin. The troponin complex consists of three subunits: troponin T, which binds to tropomyosin and facilitates contraction; troponin I, which binds to actin and inhibits actin-myosin interactions; and troponin C, which binds to calcium ions [2,6]. The amino acid sequences of the skeletal and cardiac isoforms of cardiac troponin T and troponin I are sufficiently dissimilar and, therefore, differentially detectable by monoclonal antibody based assays. Troponin C is not used clinically because both the cardiac and skeletal muscle share troponin C isoforms. Cardiac troponin I is 13 times more abundant in the heart than creatine kinase MB isoenzyme, so the signal-to-noise ratio associated with troponin I is much more favorable for the detection of minor amounts of cardiac damage. Cardiac troponin T is as abundant as troponin I in the heart [7].

Origin of cardiac troponin release

Normally, cardiac troponins T and I are not detectable in the blood of healthy persons. Release of these troponins can occur when myocytes are damaged by a variety of conditions, such as trauma, exposure to toxins, inflammation, and necrosis due to occlusion of a portion of the coronary vasculature [2-4,8]. The majority of cardiac troponin T and cardiac troponin I is bound to myofilaments, and the remainder is free in the cytosol. When myocyte damage occurs, the cytosolic pool is released first, followed by a more protracted release from stores bound to deteriorating myofilaments [9].

Abnormal values have been described in various conditions not related to acute coronary disease, like myocarditis, pulmonary embolism, acute heart failure, septic shock, and as a result of cardiotoxic drugs as well as after therapeutic procedures, such as coronary angioplasty, electrophysiological ablation, or electrical cardioversion [3]. The mechanisms of release and clearance of cardiac troponins T and I are complex and incompletely understood in these pathological conditions. Although both are structural proteins, it has been suggested that cytosolic pools of these proteins are released into the circulation after cell injury. The cytosolic pool for cardiac troponin T was estimated at 6% to 8% of total cardiac troponin and that for soluble cardiac troponin I at 2.8% of total cardiac troponin. Release of cardiac troponin T may be related to transient leakage from the cytosolic component due to loss of sarcolemmal integrity during reversible ischaemia, or from its continuous release when ischaemic injury is irreversible [3,10].

How is heart tissue damaged in sepsis?

The high prevalence of elevated serum levels of cardiac troponins in septic shock raises the question of what mechanism results in troponin release in septic shock. Proposed mechanisms include focal ischemia, and direct cardiac myocytotoxic effects of endotoxins, cytokines or reactive oxygen radicals [4,11]. In addition, activation of many intracellular pathways may cause degradation of free troponin to lower molecular weight fragments, which are released into the systemic circulation because of increased membrane permeability [9,11]. The current understanding of myocardial dysfunction in sepsis is that there is no evidence of global coronary hypoperfusion. Tools for assessing tissue and heart dysfunction have, however, evolved and enable us to reconsider the above assumption as a universal concept. In this respect, microvascular dysfunction is now considered an intrinsic aspect of sepsis sequelae. Indeed, evidence suggests that sepsis may induce perturbations in regional coronary blood flow and microvascular failure leading to myocardial ischemia [12].

Myocardial depressant substances

The phenomenon of myocardial depression can be mediated by circulating depressant substances, which until now have been incompletely characterized. Among those possible candidates, tumor necrosis factor (TNF), IL-1β and IL-6 play a central role in septic myocardial dysfunction [13]. TNF-α, alone or in association with IL-1β, has been implicated in the pathophysiology of septic myocardial dysfunction [13]. Proposed mechanisms of TNF-α-induced myocardial depression include the activation of the neutral sphingo-myelinase, and suppression of the calcium transient and nitric oxide pathways. TNF-α can also modulate tissue destruction and biosynthesis/activation of intracellular proteases [13]. For example, TNF-α may induce activation of calpains and caspases that could participate in the degradation of crucial cardiac contractile proteins, including troponins. Upon activation by calcium, active calpain is released by calpastatin and cleaves cardiac troponin I at the carboxyl terminus to produce the cardiac troponin I degradation fragment [13]. Caspases, the executioners of apoptotic cell death, also induce sarcomere disarray and are involved in the cleavage of α-actin, α-actinin and troponin T [14]. Alternatively, TNF-α may have an important role in cardiac injury through a variety of mechanisms, including second messenger pathways, arachidonate metabolism, protein kinases, oxygen free radicals, nitric oxide, transcription of a variety of cytotoxic genes, regulation of nuclear regulatory factors, ADP-ribosylation and, potentially, DNA fragmentation [13]. In this setting, histology of transgenic mice specifically overexpressing TNF-α in the heart shows hypertrophied interstitial connective tissue cells associated with focal myocyte degeneration and injury [13,15]. Transmission electron microscopy further demonstrated myofibril disarray and breakdown in TNF-α transgenic mouse heart [13,16]. Altogether, these derangements in heart tissue architecture could participate in the breakdown of sarcomeric proteins and their release in the systemic circulation.

Leukocyte and reactive oxygen species

Reactive oxygen species may play a role in the induction of several types of organ failure, including that of the heart, following the development of sepsis. Leukocyte derived superoxide and its daughter molecules are thought to be a major cause of heart injury in sepsis [17]. In addition, activated NADPH oxidase complexes and mitochondria are also potential sources of free radicals in the septic heart, which may have multiple potential sites of action [18]. Under pathophysiological conditions, dramatically elevated levels of reactive oxygen species may cause significant damage to cellular proteins and membranes as well as to nucleic acids, leading to single strand breaks and chromosomal alterations, which are all likely to induce cardiac cell death. Consistent with this hypothesis are the fascinating findings of Ammann and colleagues [19], who reported that plasma troponin levels became positive during leukocyte recovery in aplastic patients with septic shock and indicated poor outcome.

Myocardial perfusion abnormalities

Typically, global myocardial ischaemia has not been considered a critical factor of septic heart dysfunction [20,21]. Detailed analysis of existing literature may, however, lead to the contrasting conclusion that myocardial ischemia or microcirculation abnormalities are present in septic shock. Experimental studies suggest that generalized microvascular dysfunction is a prominent feature of septic shock and is probably an important factor in the heart, as elsewhere [22]. This could lead to relative ischaemia, microvascular shunting, or flow heterogeneity secondary to mechanisms such as endothelial dysfunction, leucocyte plugging of capillaries, interstitial edema and free radical production. Growing evidence suggests that reversible mismatched perfusion metabolism areas inherent to local redistributive microcirculatory adjustment are present in experimental sepsis, suggesting an ischemic component is partially responsible for heart dysfunction [23-25]. Specifically, decreased myocardial microcirculatory flow and random oxygen consumption have been experimentally demonstrated by means of positron emission tomography imaging in endotoxic shock [24].

Heart apoptosis

Despite extremely low levels of myocyte nuclear apoptosis, caspase activation has been implicated in sarcomere disarray and contractile dysfunction in various models of myocardium injury [26]. Caspase activation participates in the regulation of cardiac contractility and its inhibition might reverse depressed contractility. Many putative caspase cleavage sites in cardiac contractile and structural proteins may be identified through data bank research with caspase cleavage motifs. The existence of such cleavage sites explains the findings that exposure of myofibrillar proteins to active caspase 3 results in α-actin, α-actinin and troponin T and myosin light chain cleavage [14]. In experimental sepsis, our studies suggest that activation of caspase 3 plays an important role in endotoxin-induced cardiomyocyte dysfunction, which is related to changes in calcium myofilament response, troponin T cleavage and sarcomere disorganization [26].

What mechanisms of troponin increase are possible in clinical sepsis?

Does cardiac ischemia occur in septic patients?

Two elegant studies have shown that coronary blood flow is increased and not decreased in septic shock, even if energetic substrate extraction is altered [20,21]. Preservation of coronary flow, net myocardial lactate extraction, and increased availability of oxygen to the myocardium argue against global ischemia as a cause of septic myocardial depression. In addition, nuclear magnetic resonance studies have shown normal myocardial high energy phosphate levels. In these studies, however, myocardial ischemia is difficult to rule out. First, the results of these studies suggest evidence of myocardial hypoxia (zero or negative lactate uptake) in 15% of studied patients [21]. Second, autopsies of septic patients provide circumstantial evidence that histological changes can be related to heart ischemia. For example, in a retrospective review of autopsy findings in 71 patients, Fernandes and colleagues [27] noted abnormalities in the myocardium, including interstitial myocarditis (27%), interstitial edema (28%), and muscle-fiber necrosis (7%). These data also support an opinion that structural injury to the contractile apparatus or microcirculation of the heart may contribute, at least partly, to myocardial dysfunction in sepsis [28].

Does demand ischemia exist in septic shock?

Cardiac output is typically increased in sepsis, meaning increased work for the cardiac pump, that is, increased oxygen demand. Tachycardia can further decrease oxygen supply because diastolic time, during which myocardial perfusion occurs, is reduced. Coronary flow reserve can thus be reduced, with a potential mismatch between oxygen demand and supply causing demand ischemia. In addition, aggressive inotropic treatment to boost systemic oxygen delivery may increase the incidence of cardiovascular complications and adversely affect outcome in fluid resuscitated septic patients. It is quite possible that elaborate attempts at prolonged resuscitation could either cause or disclose ischemic myocardial damage. Increased cardiac filling pressures and increased wall stress may contribute to myocyte damage and microinjury in septic shock [2].

Could increase of cardiomyocyte permeability explain troponin leakage?

Circulating mediators such as TNF-α have been implicated in increased permeability of sarcolemmic cardiomyocyte membrane, a phenomenon that could explain troponin release without irreversible injury [9]. TNF-α may increase the permeability of endothelial monolayers to macromolecules and lower molecular weight solutes and it is likely that similar alterations in permeability also occur at the level of myocyte cell membranes, thus leading to leakage of cardiac troponin I [12]. Indeed, release of myocardial enzymes from mammalian myocardiocytes into cell supernatant has been demonstrated during limited periods of hypoxia [29]. In human volunteers, no correlation between plasma levels of TNF-α and troponin could be found in endotoxin-treated volunteers, suggesting that TNF-α alone may not be sufficient to induce increased permeability [30]. In sharp contrast, levels of TNF-α, its soluble receptor and IL-6 are significantly higher in troponin-positive septic shock patients than those of troponin-negative patients, suggesting that cytokines in combination may provoke an increase in membrane permeability and troponin release [19].

Are increased troponin levels related to ischemic cardiac tissue damage in clinical sepsis?

Many studies in sepsis have shown that continuous ECG monitoring and transthoracic echocardiography examination at diagnosis do not disclose developing ischemia and exclude myocardial infarction [19,31-37]. In troponin-positive septic shock patients, the presence of myocardial ischemia has been excluded based upon results of stress echocardiography [19,31,38]. It should be pointed out, however, that stress echocardiography cannot definitely exclude micro-embolization from non-flow limiting unstable plaques as well as local wall motion abnormalities as a cause of elevated troponins. In this specific context, even very small episodes of myocardial necrosis (< 1 g) may be associated with significant troponin increases [2].

The presence of some degree of focal cardiac necrosis in septic patients has been emphasized by recent anatomopathological findings. Indeed, troponin-positive septic shock patients tend to show more pronounced histological abnormalities than troponin-negative septic shock patients [31,37]. Specifically, contraction band necrosis, an early marker of irreversible myocyte injury, and sarcoplasmic fibril rupture are more frequent in troponin-positive septic shock patients [37]. Contraction band necrosis is believed to result from calcium overload and its presence is typically associated with focal ischemia reperfusion injury and the use of high catecholamine concentrations.

Does increased troponin level indicate cardiac dysfunction and poor outcome in clinical sepsis?

A correlation between troponin level and requirements for inotropic support has been mentioned by some authors [36,39], whereas others have shown opposite results [37,38]. In patients with increased troponin levels, evaluation of myocardial performance during septic shock has been performed by the means of left ventricular stroke work index calculation [5,39] and evaluation of systolic function by echocardiography [19,33,35,37,38,40]. Consistently, estimates of left ventricular ejection fraction and fractional area contraction correlate negatively with increased levels of cardiac troponin I in both adults and children with septic shock [35,38,41,42]. Also, serial determinations of cardiac troponin I show a negative correlation between serum concentrations of cardiac troponin I and myocardial function (echocardiography fractional area contraction less than 50%) [41]. However, a correlation between left ventricular dysfunction and increased levels of cardiac troponin I is not a universal finding in septic shock patients [43]. The reason for these contrasting results has not been reconciled. However, it should be pointed out that several factors may complicate the diagnosis of sepsis-induced myocardial dysfunction in humans and echocardiography derived parameters may not reflect actual myocardial contractility and dysfunction [41,42].

In addition to global systolic and diastolic performance evaluation, tissue velocity imaging for myocardial strain and strain rate imaging is an important development in the field of cardiac ultrasound that provides quantitative information for analysis of myocardial motion. Increased wall strain and regional wall motion abnormalities in septic shock could be part of the septic myocardial dysfunction pattern and account for cardiac myolysis. Although regional wall motion abnormalities have been observed in some positive-troponin cases [36], there is no information with respect to perturbations in tissue Doppler derived myocardial strain and strain rate in septic shock patients.

Eventually, a prognosis of sepsis depends on the severity of organ dysfunctions, in particular, cardiovascular failure. Whether an elevated troponin level represents a critical and independent parameter of outcome has been debated in many clinical studies [5,8,20,34,36,40-43]. Studies in unselected critically ill patients yield the consistent information that mortality among troponin-positive patients is higher than troponin-negative patients, irrespective of the cause of troponin increase. In studies restricted to patients with sepsis, elevated troponin levels have been shown to be related to the severity of the disease. Overall, these results are very similar in showing that troponin elevation indicates a worse myocardial function and unfavourable outome [5,19,31,34,36,37,39].

It should be pointed out, however, that the relative expected and documented ranges of troponin that can be seen in sepsis are rather difficult to depict because there is huge variability in the sensitivity of assays (Table 1). The appropriate cut-off value for each assay is unique and cannot be compared with any other. These differences are due in part to the heterogeneity of the antibodies and matrix components of the assays. They are also due to the fact that there are various fragments of troponin that circulate, and the antibodies used in the various assays detect these fragments differently [3,7,10].

Conclusion

Although the mechanisms of troponin release into plasma during sepsis are not clearly established, cardiac troponin I is an indicator of myocardial injury in septic patients and is potentially associated with myocardial depression and poor outcome. There is evidence from several small studies that elevated cardiac troponin levels in patients with sepsis indicate myocardial dysfunction and a poor prognosis. However, further studies are needed to elucidate the potential of troponins to characterize the severity and course of the septic cardiomyopathy. Cardiac troponin I, in association with markers of myocardial depression such as natriuretic peptides, seems to be an early factor of prognosis and cardiac dysfunction in patients with sepsis.

References

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The relation between the incidence of hypernatremia and mortality in patients with severe traumatic brain injury

                      Umberto Maggiore, Edoardo Picetti, Elio Antonucci, Elisabetta Parenti, Giuseppe Regolisti,
                      Mario Mergoni, Antonella Vezzani, Aderville Cabassi and Enrico Fiaccadori

                                                                              Critical Care 2009, 13:R110 (doi:10.1186/cc7953)

Abstract

Introduction

The study was aimed at verifying whether the occurrence of hypernatremia during the intensive care unit (ICU) stay increases the risk of death in patients with severe traumatic brain injury (TBI). We performed a retrospective study on a prospectively collected database including all patients consecutively admitted over a 3-year period with a diagnosis of TBI (post-resuscitation Glasgow Coma Score ≤ 8) to a general/ neurotrauma ICU of a university hospital, providing critical care services in a catchment area of about 1,200,000 inhabitants.

Methods

Demographic, clinical, and ICU laboratory data were prospectively collected; serum sodium was assessed an average of three times per day. Hypernatremia was defined as two daily values of serum sodium above 145 mmol/l. The major outcome was death in the ICU after 14 days. Cox proportionalhazards regression models were used, with time-dependent variates designed to reflect exposure over time during the ICUstay: hypernatremia, desmopressin acetate (DDAVP) administration as a surrogate marker for the presence of central diabetes insipidus, and urinary output. The same models were adjusted for potential confounding factors.

Results

We included in the study 130 TBI patients (mean age 52 years (standard deviation 23); males 74%; median Glasgow Coma Score 3 (range 3 to 8); mean Simplified Acute Physiology Score II 50 (standard deviation 15)); all were mechanically ventilated; 35 (26.9%) died within 14 days after ICU admission.
Hypernatremia was detected in 51.5% of the patients and in 15.9% of the 1,103 patient-day ICU follow-up. In most instances hypernatremia was mild (mean 150 mmol/l, interquartile rang 148 to 152). The occurrence of hypernatremia was highest (P  = 0.003) in patients with suspected central diabetes insipidus(25/130, 19.2%), a condition that was associated with increased severity of brain injury and ICU mortality. After adjustment for the baseline risk, the incidence of hypernatremia over the course of the ICU stay was significantly related with increased mortality (hazard ratio 3.00 (95% confidence interval: 1.34 to 6.51; P = 0.003)). However, DDAVP use modified this relation (P = 0.06), hypernatremia providing no additional prognostic information in the instances of suspected central diabetes insipidus.

Conclusions

Mild hypernatremia is associated with an increased risk of death in patients with severe TBI. In a proportion of the patients the association between hypernatremia and death is accounted for by the presence of central diabetes insipidus.

Hypernatremia, a water balance disorder encountered in about 6 to 9% of critically ill patients, has been associated with an increased risk of death and complications in some recent retrospective studies in general intensive care units (ICUs) [1-3]. Patients with severe traumatic brain injury (TBI) have a high risk of developing hypernatremia over the course of their ICU stay, due to the coexistence of predisposing conditions such as impaired sensorium, altered thirst, central diabetes insipidus (CDI) with polyuria, and increased insensible losses [4].Moreover, these patients often receive mannitol or hypertonic saline solutions, with the aim of reducing cerebral edema and controlling intracranial pressure [5]. In this clinical setting, it is not known, however, whether increased serum sodium (Na) is an independent risk factor for death, or is simply a surrogate marker of illness severity.
It has been shown that almost 20% of patients with subarachnoid hemorrhage develop hypernatremia, a complication bearing an increased risk of death [6]. On the other hand, in a recent series of patients from a neuro-ICU, hypernatremia was documented in only 8% of them; moreover, only the more advanced forms of this disorder (that is, serum Na exceeding 160 mmol/l) were associated with increased mortality [7]. These conflicting findings leave the question of the true clinical significance of moderate increases in serum Na (for example, between 145 and 160 mmol/l) unresolved. We therefore designed the present study in order to verify whether the occurrence of hypernatremia during the ICU stay is an independent risk factor of death in patients with severeTBI (Glasgow Coma Score ≤ 8).

We studied all adult patients consecutively admitted with a diagnosis of severe TBI from May 2004 to April 2006. The operational definition of severe TBI was a post-resuscitation Glasgow Coma Score of 8 or less at ICU admission. The ICU of the Anesthesia and Intensive Care Department is located in part of the 1,200-bed Parma University Medical School Hospital, a tertiary academic referral institution. The ICU contains 20 general intensive care beds, staffed with fulltime intensive care specialists. The unit provides all critical care services to patients admitted to the Emergency Department for head injury with or without polytrauma, as well as postoperative care for the neurosurgery services. The same ICU serves as a neurotrauma ICU for a catchment area of about 1,200,000 inhabitants.

Regarding the TBI patients admitted to the ICU, we prospectively collected data concerning demography, clinical and laboratory characteristics, prognostic factors and outcome, which were entered into an electronic database. For each patient the following data were obtained at admission: age, sex, cause of admission classified by type of trauma, premorbid functional status, acute and chronic co-morbidities, brainCT-scan data, Simplified Acute Physiology Score II score [8], Injury Severity Score [9], Glasgow Coma Score [10], hemodynamics, respiratory status and mechanical ventilation, blood gases, serum electrolytes, serum glucose, hemoglobin, leukocyte and platelet counts, renal function, and urinary output. Additional data were collected on a daily basis: serum electrolyte levels (all values, if more than one value was available), serum glucose, administered medications and fluids, including vasopressin and osmotic therapy (defined as the use of 3% or 5% saline or mannitol to treat cerebral edema or raised intracranial pressure), urinary volume, mechanical ventilation, and intracranial pressure (ICP) when available. The use of desmopressin acetate (DDAVP) was taken as a surrogate marker of suspected CDI. Finally, data concerning ICU complications, ICU mortality and inhospital mortality were also collected. All subjects received standard care for TBI according to current guidelines [11,12]. The protocol dictated that routine clinical practice would never change for the purpose of study data collection. The Ethical Committee of the Parma University Medical School approved the study and waived the need forwritten informed consent by patients' next of kin.

Some clinical parameters were assessed hourly, and other parameters were assessed every 4 hours, 6 hours, 8 hours or once daily. Serum Na was assessed an average of three timesa day. The number of determinations, however, tended to decrease with the increase in length of the ICU stay. To simplify the analysis, we created variates referring to the day of stay as the fundamental time unit.
We adopted three indexes to define the presence of serum Na disorders - daily serum Na, daily urinary output (polyuria being the marker of renal water loss), and daily administration of DDAVP. Urinary output was the least reliable of these three indexes, as it was frequently missing. Some of the patients did not have complete (that is, 24-hour) urine output recorded. This problem occurred more frequently on the day that the most severely ill patients were admitted (in fact, missing urine output was significantly and independently associated with increased mortality; data not shown). In some other cases, exact urine output recording was missing during the hospital stay because the patients received intermittent urinary catheterization.
Finally, urinary output was influenced by DDAVP medication, which the doctors administered whenever they noted an increase in urinary output (usually, an abrupt increase of urinary output to more than 250 ml/hour for 2 hours, in the absence of diuretic therapy), with the result of curbing the increased urinary output. At variance with urinary output, there were only nine missing values regarding serum Na and no missing values concerning DDAVP use. For the purpose of the analysis, the presence of hypernatremia was expressed as a time-dependent indicator variate. Hypernatremia was defined as serum Na >145 mmol/l on at least two occasions during 1 day of ICU stay. In 35% of the cases there was only a single daily determination, although this occurred for the most part during the second week of stay. The nine missing daily Na measurements were replaced by the value of the previous day of the ICU stay.
The use of DDAVP, which we took as a surrogate marker for the presence of CDI, was defined by a time-dependent indicator variate. To avoid the possibility that DDAVP could be interpreted as a marker of established brain death rather than a death predictor, the coding of the variate switched from 0 to 1 starting from the day after the first DDAVP administration. We also created time-dependent indicator variates for the presence of daily urinary output above 3 l and for the use of mannitol and hypertonic saline solutions, and created timedependent continuous variates for glucose levels and hyperglycemia (two daily serum glucose values above 10 mmol/l).

We used Stata Release 10 software (2007; StataCorp, College Station, TX, USA) for all analyses.

With the use of Cox proportional-hazards regression models, we examined the relation between 14-day ICU mortality and hypernatremia, polyuria (defined as urinary output >3 l day), and the use of DDAVP (that is, presence of CDI) over the course of the ICU stay. In order to adjust the estimates for the baseline risk of death, we used the core + CT score from the International Mission for Prognosis and Clinical Trial (IMPACT) prognostic model [13]. This score takes into account the extension of brain injury detected by CT scan at admission. Additionally, we adjusted the models for common determinants of polyuria (use of hypertonic Na solutions, intravenous mannitol, hyperglycemia), which may also be potentially associated with increased mortality in this category of patients. In the principal analyses, patients were censored at the time of discharge. In a further analysis, all patients discharged from the ICU before day 14 were considered as surviving beyond day 14, with the exception of the patient who died at day 12 after discharge from the ICU. The covariate status after discharge from the ICU was not known, thus the last covariate before discharge was carried forward until the day of censoring or death. We do not report the results of these analyses because they were virtually identical to those of the main analyses. We examined linearity of the continuous variates by the residual- based plots [14]. We tested departures from the proportional assumption using the procedure proposed by Grambsch and Therneau based on Shoenfeld residuals [15]. We used the Efron method to handle tied failures, the likelihood ratio test to compute P values, the profile likelihood for the point estimate and 95% confidence intervals [16]. We also decided to estimate the relation between hypernatremia and death after having stratified the data according to the presence of suspected CDI (that is, DDAVP use). With this aim in mind we fitted an interaction term between DDAVP use and hypernatremia in a stratified Cox regression model where DDAVP use was included as the stratum variable. To gain deeper insight into the nature of the observed relation between hypernatremia and mortality in the presence of CDI, we computed a measurement to explain variation in survival time (namely, R2), which is appropriate for use with the unstratified
Cox regression models with time-dependent covariates.vFor this purpose we used the strph2 program, which computes Rosyton's modification of O'Quingley, Xu and Stare's modification of Nagelkerke's coefficient of determination for survival models [17,18]. We also compared the models with the Bayes information criterion. The model with the smallest value of the Bayes information criterion was considered better. The Bayes information criterion is a likelihood-based measure of fit, which adds a penalty for added covariates based on sample size. It seeks to balance the competing desire of finding the best model (in terms of maximizing the likelihood) with model parsimony (only including those covariates that significantly contribute to the model). For the computation of the Bayes information criterion we considered the sample size to be equal to 130 (that is, thenumber of patients).

Results

We enrolled 130 patients with severe TBI. The characteristics of the population in our study are summarized in Table 1. All patients were mechanically ventilated, about one-half of them by tracheostomy. Only 52 patients (40%) suffered from an isolated TBI, while about one-half of the others also had thoracic trauma with lung involvement. A relevant proportion of the patients had skull fracture, brain contusion, or subarachnoid hemorrhage. Thirty-two patients had no pupillary light reflex at admission. CT scan at admission showed cerebral swelling with a midline shift in one-quarter of the patients (median shift, 10 mm) and cerebral herniation in about one-sixth of them.
Forty-one percent underwent neurosurgical emergent procedures after admission to the ICU. Only 5% of the patients were severely hypotensive at admission, but about one-half of them required vasopressor administration during their ICU stay. Of the 130 patients, 34 (26.2%) died in the ICU within 14 days after admission, after a total follow-up of 1,103 patientdays. One patient died on day 12 (that is, within 14 days after admission), when he had been already discharged from the ICU. Twenty-nine of the 34 deaths in the ICU occurred within 3 days after admission. Eleven patients were discharged from the ICU within 3 days, and another 42 patients were discharged between day 4 and day 14. The total inhospital mortality was 41/130 (31.5%).

The mean serum Na at admission was 139 mmol/l (standard deviation 3.9). Only three patients (2.3%) had serum Na above 145 mmol/l (maximum value 149 mmol/l). Altogether, 15.9% of the follow-up days were complicated by hypernatremia - occurring at least once in 51.5% of the patients for 31.0% of the duration of their stay in the ICU, even though it was mild. In fact, the highest serum Na in patients with hypernatremia was, on average, 150 mmol/l (range 146 to 164, interquartile range 148 to 152). Urinary output was missing in 153 out of the 1,103 ICU days of follow-up. Unfortunately, the data on urinary output were not randomly missing. In fact, ICU mortality in patients with at least one missing urinary output was 51.2% (21/41), in comparison with 16.8% (15/89) in the remaining patients (P < 0.001). Polyuria was detected in 34.4% (327/950) of ICU days, and occurred in 76.0% of the 108 subjects in whom urinary output was recorded. In the instances of ascertained polyuria, the mean urinary output was 4,150 ml/day - the maximum being 8,850 ml/day. Twenty-five patients (19.2%) received DDAVP at least onceover the course of their ICU stay. DDAVP, however, was administered only during 5.9% of the days of the entire followup.
Patients receiving DDAVP had a higher urinary output and serum Na than those not receiving this medication (median urinary output 3,720 vs. 2,480 ml/day, P < 0.001; median serum Na 148 vs. 142 mmol/l, P < 0.001). For each patient the probability of receiving DDAVP increased with the onset of hypernatremia (odds ratio = 3.41, P = 0.009 by conditional logistic regression). Accordingly, 29.9% (20/67) of the patients who developed hypernatremia at any time during their ICU stay received DDAVP, compared with 7.9% (5/63) of the others (odds ratio = 4.88, P = 0.003 by unconditional logistic regression).

Age (years) 51.8 (23)

Male gender 96 (74%)

Injury Severity Score 30.3 (7.7)

Simplified Acute Physiology Score II Score 49.8 (14.6)

Glasgow Coma Score 3 (3 to 8)

Motor score 1 (1 to 5)

1 78 (60.0%)

2 11 (8.5%)

3 11 (8.5%)

4 6 (4.6%)

5 24 (18.5%)

Absence of pupillary reflex

Both 21 (16.2%)

One 11 (8.5%)

Systolic arterial pressure <90 mmHg 7 (5.4%)

Tracheal intubation

Prehospital 105 (81.0%)

At admission 25 (19.2%)

Hypotension 16 (12.3%)

Diabetes 9 (6.9%)

History of heart disease 21 (16.2%)

History of arterial hypertension 24 (18.5%)

Chronic renal failure 1 (0.8%)

spO2 (pulse oxymetry) (%) 97.3 (5.7%)

Hypoxia 11 (8.5%)

Plasma HCO3 (mmol/l) 21.1 (3.4)

pCO2 (mmHg) 38.9 (7.7)

Midline shift on brain CT 32 (24.6%)

Cerebral edema on brain CT 31 (23.8%)

Cerebral herniation on brain CT 21 (16.2%)

Subarachnoid hemorrhage 62 (47.7%)

Epidural hematoma 19 (14.6%)

Presence of petechial hemorrhages 15 (11.5%)

Subdural hematoma 72 (55.4%)

Cerebral contusion 67 (51.5%)

Obliteration of the third ventricle or basal cisterns 31 (23.8%)

CT classification

I 13 (10%)

II 6 (4.6%)

III/IV 9 (6.9%)

V/VI 102 (78.5%)

Urgent neurosurgerya 54 (41.5%)

Polytrauma 78 (60.0%)

Thoracic trauma 89 (68.5%)

Abdominal trauma 25 (29.2%)

Continuous variates presented as mean (standard deviation) or median (range); categorical variates presented as number (percentage). aWithin 4 hours after intensive care unit admission.
Mannitol was administered in 49.2% (64/130) of the patients

over 27.9% (308/1,103) of the days spent in the ICU. Hypertonic saline solutions were administered in 36.1% (47/130) patients and over 14.3% (158/1,103) of the days they spent in the ICU. These interventions did not bear any apparent relation to serum Na or DDAVP administration (data not shown).
The 51 patients in whom the concomitant measurement of serum Na and ICP was available did not show any difference in ICP according to the presence of hypernatremia (median ICP 16 mmHg in both instances, P = 0.67). The average of the daily mean serum glucose was 7.7 mmol/l (range 3.3 to 17.0). Hyperglycemia occurred at least once in 37.7% (46/130) of the patients during 7.7% (85/1,103) days of stay in the ICU. There was no significant difference in mean glucose levels and in the rate of hyperglycemia according to DDAVP use or the presence of hypernatremia (data not shown).

Patients who died on days 2 and 3 of their ICU stay had the highest increase in daily average serum Na between days 1 and 2, while receiving DDAVP more often than the others. In fact, the 13 patients who died on day 2 had a mean increase of serum Na of +3.7 mmol/l, which was higher than that observed in the same period in the 103 patients still alive in the ICU on day 2 (+1.5 mmol/l; P = 0.020). The mean increase in the four patients who died on day 3 was +4.6 mmol/l; that is, greater than that observed in the 96 patients who were still alive in the ICU on day 3 (+1.4 mmol/l; P = 0.019). Accordingly, patients who died on days 2 and 3 had received DDAVP more frequently than those who remained alive in the ICU. In fact, on day 2 the proportion of DDAVP use was 3/13 (23.1%) among patients who died and was 3/103 (2.9%) among those who were still alive (P = 0.018). On day 3, this proportion of DDAVP use was 3/4 (75.0%) and 4/96 (4.2%), respectively (P = 0.001). Overall, 56% (14/25) of the patients who received DDAVP at any time during their ICU stay died, compared with 19.0% (20/105) of the others (P = 0.001). These findings were mirrored by the results of Cox proportional- hazards regression analysis. As shown in Table 2, hypernatremia was associated with a threefold increase in the hazard of ICU death even after adjustment for baseline risk (hazard ratio = 3.00 (95% confidence interval: 1.34 to 6.51; P = 0.003)). The additional adjustment for DDAVP use, however, halved the estimated relative increase in mortality (hazard ratio of hypernatremia adjusted for DDAVP use = 2.04; P = 0.092). On the other hand, after adjustment for hypernatremia, the hazard ratio associated with DDAVP use was 3.88 (P =0.005)  The R2 values of the model that included the baseline risk were 0.543, 0.596, and 0.624 for hypernatremia, for DDAVP, and for hypernatremia + DDAVP, respectively. As shown in Table 2, after stratifying the model according to DDAVP use (that is, presence of suspected CDI), hypernatremia did not bear any additional prognostic information in the presence of CDI (hazard ratio = 0.58; P = 0.57), while retaining its importance in the other instances (hazard ratio = 4.20; P = 0.004) (P = 0.060 for the test of the difference between the two hazard ratios).
Additional adjustment for the use of mannitol, hypertonic saline solution and hyperglycemia did not change the findings (data not shown). In fact the latter, which was associated with increased mortality, was evenly distributed according to the presence of hypernatremia and the use of DDAVP (data not shown).

Discussion

To our knowledge, the present study is the first that has been specifically aimed at investigating the incidence and clinical significance of hypernatremia occurring during the course of the ICU stay in a large series of patients with severe TBI. The study shows that, in the immediate post-TBI period, mild hypernatremia is associated with an increased risk of death - although, in a proportion of the patients, this association is due to the occurrence of CDI, a marker of the extension and severity of brain injury.
We acknowledge that our study has the significant weakness of using DDAVP as the major criterion for diagnosing CDI, which, at best, can be considered a surrogate index only. Agha and colleagues defined CDI in the immediate post-TBI as serum Na >145 mmol/l in the presence of both polyuria (>3.5 l/day) and diluted urine (osmolality < 300 mOsm/l) [19,20].
We could not use the same criteria for the diagnosis of CDI, in as much as data on urinary output were missing in many instances and urine osmolality was not measured. Our analyses, however, showed a CDI incidence of 19.2% (25/130); that is, well within the range of 15 to 26% documented by the previous studies on the subject [19-21]. This concordant finding suggests that in our series CDI was correctly classified. In another small series of TBI patients the incidence of CDI was much lower [22], probably owing to the exclusion of patients with incomplete data. Similarly to those studies, we found that CDI is associated with an increase in the severity of brain injury [19] and in the risk of death [21,22]. Finally, our analysis was adjusted for several factors potentially capable of confounding the relation between hypernatremia, CDI and mortality; namely, the use of hypertonic saline solution, intravenous mannitol, serum glucose levels, and the incidence of hyperglycemia (23-25].
The high incidence of CDI that both we and other workers found [19-21] is not unexpected in patients with TBI [26]. The awareness of the importance of CDI is such that a decade ago a small randomized controlled study was designed to evaluate whether or not the use of DDAVP in all brain-dead donors (by definition, in patients with the most severe degree of brain injury) could improve kidney transplant function [27,28]. Injury of the hypothalamus and pituitary generally occurs concomitantly, and is seen at autopsy in up to 60% of patients dying from head trauma [22]. Edwards and Clark reviewed a series of pathological studies of fatal head injury and reported that hemorrhage or infarction in the hypothalamus was detected in 42% of cases [29]. The petechial hemorrhage areas in the anterior hypothalamic nuclei and neurohypophysis can be caused by forces transmitted to the head on impact, by increased ICP resulting from the brain edema, by shearing stresses that produce disruption of the pituitary stalk, and by the hypothalamic-hypophyseal portal system [30].
Our results confirm the recent finding from Hadjizacharia and colleagues that CDI is an independent risk indicator of death
 In fact, in our study the presence of CDI provided additional prognostic information regarding the extension of brain injury with respect to the CT scan at admission, because the relative hazard of mortality associated with CDI was adjusted for the CT IMPACT prognostic model as assessed at ICU admission. We found that the incidence of hypernatremia (occurring in about one-half of the patients at any time duringthe ICU stay, with 16% of ICU days complicated by this sodium disorder) was more than double the incidence of CDI.
This incidence is higher than that reported by Qureshi and colleagues (19%) [6] and by Wartenberg and colleagues (22%) [31,32]. The latter two series, however, included patients with subarachnoid hemorrhage rather than with TBI; moreover, the study by Qureshi and colleagues defined hypernatremia by serum Na at admission or on day 3, and the study by Wartenberg defined hypernatremia as serum Na >150 mmol/l.
Another study from a very large database (The Traumatic Coma Data Bank) reported an occurrence of electrolyte abnormalities in patients affected by TBI as high as 59%, with a peak incidence in the first 24 to 96 hours [33]; unfortunately, the true incidence of hypernatremia cannot be inferred from the data presented in the study, as all types of electrolyte disturbanceswere pooled together.
To our knowledge, ours is the first study documenting the incidence of hypernatremia during the ICU stay in severe TBI patients. The definition of hypernatremia in our study refers to the first 14 days of ICU stay, and it is robust since it requires that at least two values of serum Na be >145 mmol/l in all patients receiving multiple daily determinations of serum sodium. The finding that the incidence of CDI was lower than that of hypernatremia suggests that only a minority of the cases of hypernatremia were due to CDI. In most cases hypernatremia was generally mild, probably because the prompt administration of DDAVP by the attending physician prevented excess water loss if CDI was present. Van Beek and colleagues recently examined the relation between serum Na and outcome using data from the IMPACT database [34]. Their analysis took into consideration only serum Na values at admission, however, not those obtained during the ICU stay.
At variance with what is observed during the ICU stay, patients with TBI show hypernatremia only rarely at admission, which in fact was detected only in 5% of the patients of the IMPACT study and in 2.3% of the patients in our study. In that setting Van Beek and colleagues defined high serum Na as Na levels above the 75th percentile, corresponding to 142 mmol/l [34]; that is, a level lower than the standard cut-off value currently used for defining hypernatremia.
Our findings indicate that in a proportion of the patients the relation between hypernatremia and mortality is accounted for by the coexistence of CDI, whereas hypernatremia by itself could represent an independent risk factor of death in those patients lacking CDI. We recognize that our criteria for assessing CDI might have identified only its full blown forms, however, possibly leaving undetected those incomplete and subtleforms that still can cause hypernatremia; this might explain the residual relation we found between hypernatremia and death.
Further studies are needed to provide support for this hypothesis.
Finally, the relation between hypernatremia and mortality has been already documented in studies mostly dealing with patients in general ICUs [1-3,35,36], and not specifically including TBI patients. Even on the basis of the more recent literature, unfortunately based on retrospective studies only [1-3], it is not however possible to definitely exclude the possibility that hypernatremia in the ICU could simply be regarded as a surrogate marker of illness severity, rather than as an independent predictor of mortality. In the case of patients with TBI the interpretation of the relation between high serum Na levels and outcome is made even more difficult by the presence of peculiar interfering factors - such as for example CDI, as previously discussed - and the use of hypertonic saline to control cerebral edema and elevated ICP [5,33,37-43]. Hypertonic saline has actually gained major interest as a treatment option in patients with elevated ICP levels due to a wide spectrum of etiologies, such as subarachnoid hemorrhage [44-47], stroke [48,49], elective brain surgery [50], as well as other clinical conditions characterized by cerebral edema [51-53]. The proposed mechanisms of hypertonic saline action are complex, involving cell volume reduction due to fluid drawing from the brain, reduced cerebral blood volume due to ameliorated blood viscosity and rheology, greater neuroprotection through the restoring of neuronal membrane potentials, neuroinflammatory pathway modulation, and so forth [54].
It is to be noted that most available data about hypertonic saline use (either as intravenous boluses or continuous infusion) in TBI patients with high ICP levels derive from small trials, case series or retrospective studies [55-59], while only few papers deal with its possible side effects. Following the recent publication of a retrospective analysis of neurocritically ill patients including severe TBI [59], some concern has been raised about the use of continuous-infusion hypertonic saline [54]. In that study, hypertonic saline use increased the risk of hypernatremia, increased the number of infection days, increased the hospital length of stay, increased the creatinine and blood urea nitrogen serum levels, along with increasing the occurrence of deep vein thrombosis - the most severe form (serum Na >160 mmol/l) being eventually associated with an increased mortality [59]. Clearly, before recommending such treatment in clinical practice [60], we strongly need randomized-control intervention studies to confirm the safety and efficacy of hypertonic saline in the care of neurocritically ill patients.

Mild hypernatremia is frequently encountered in patients with severe TBI during the ICU stay.    

References

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Conclusions

Relation between hypernatremia and ICU mortality

Clinical and demographic characteristics at intensive care unit admission

Hypernatremia during the ICU stay

Clinical characteristic of the study population, follow-up and mortality

Fourteen-day mortality

Data analysis

Generation of variates and missing values

Data collection

Materials and methods

Study population

Introduction

Update in Tuberculosis 2008

                                                                                           Wing Wai Yew and Chi Chiu Leung

American Journal of Respiratory and Critical Care Medicine Vol 179. pp. 337-343, (2009)

GENETICS AND IMMUNOLOGY OF TUBERCULOSIS

Genetic susceptibility studies in tuberculosis (TB) may increase our understanding of protective immunity against Mycobacterium tuberculosis. Cooke and coworkers performed an initial genome-wide screen on 71 affected sibling pairs in South Africa and Malawi, followed by an independent case-control study in West Africa (1). Two novel putative loci for TB susceptibility were identified in the affected sibling pair analysis: chromosome 6p21-q23 and chromosome 20q13.31-33, with the latter showing the strongest evidence for susceptibility of any locus reported to date in human TB (maximum likelihood score 2.8; P = 0.0008). The independent, multistage genetic association study in West African populations mapped this latter region in detail, finding evidence that variations in the melanocortin 3 receptor (MC3R) and cathepsin Z (CTSZ) genes possibly play a role in the pathogenesis of TB.
As polymorphisms in cytokine genes are known to affect cytokine levels, they might also influence the outcome of infections. Selvaraj and coworkers assessed such potential associations in pulmonary TB (2). They found significantly decreased frequency of the TT genotype of the IL-2 -330 polymorphism (odds ratio [OR], 0.53; P = 0.024) in patients with pulmonary TB compared with healthy controls. The frequencies of other polymorphisms were not different between the two groups. IL-12p40 levels were significantly decreased among healthy controls with the AA genotype of the IL-12B gene polymorphism, as compared with healthy controls with the AC genotype (P < 0.05). Increased levels of IL-12p40 were observed among patients with the CC genotype of IL-12B gene, compared with patients with other genotypes (P < 0.01). These data suggest the TT genotype of the IL-2 -330 polymorphism may be associated with protection against pulmonary TB in South India. Furthermore, the +1188 polymorphism of the IL-12B gene, either alone or in combination with closely linked genes, may regulate IL-12p40 production and thus affect acquired immunity to TB.
Polymorphic genes are involved in encoding proteins involved in immunologic modulation, including interferon- and components of the major histocompatibility complex. Although single polymorphisms were found to affect host susceptibility to TB when they were considered in epidemiological studies, potential interactions between multiple polymorphisms that may affect host susceptibility have not been well delineated. Chang and coworkers hypothesized that polymorphisms in some genes related to TB response might counteract or intensify the effects of polymorphisms in other genes (3). To test this hypothesis, the investigators developed a mathematical model of antigen presentation, based on experimental data for the known effects of genetic polymorphisms and simulated time courses when multiple polymorphisms were present. They found that polymorphisms in different genes could affect antigen presentation to the same extent and thus compensate for each other. Furthermore, the investigators were able to define the conditions under which such relationships could exist. These relationships might possibly explain discrepancies in the epidemiological literature regarding the association of TB with host susceptibility genes.
Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that have important physiological roles that include remodeling of the extracellular matrix, facilitating cell migration, cleaving cytokines, and activating defensins. However, excess MMP activity can lead to tissue destruction, an event that may be implicated in immunopathologic changes, such as cavitation, associated with TB (4). Soluble factors derived from M. tuberculosis in culture were also found to synergize with TNF- to increase MMP-9 secretion by primary human bronchial epithelial cells (5). Such results show that host- and pathogen-derived factors can act together in the immunopathological mechanisms associated with TB. O'Kane and coworkers have recently found that infection of monocytes by M. tuberculosis resulted in prostaglandin-dependent secretion of oncostatin M, which synergized with TNF- to drive functionally unopposed fibroblast MMP-1/3 secretion in TB (6).
Dou and coworkers investigated the immune adjuvant effects of interleukin-21 (IL-21) on DNA vaccine constructs expressing the M. tuberculosis antigen Ag85A by comparing immune responses in mice inoculated with DNA vaccine constructs expressing both Ag85A and IL-21 to those induced by DNA vaccine constructs expressing Ag85A alone or Bacillus Calmette-Guerin (BCG) (7). IL-21 was found to be a promising immune adjunct for enhancing the immunogenicity of DNA vaccines containing Ag85A.
Agger and coworkers described a cationic adjuvant formulation (CAF01) consisting of a delivery vehicle and synthetic mycobacterial cord factor as an immunomodulator (8). CAF01 primed strong and complex immune responses. Using ovalbumin as a model vaccine antigen in mice, antigen-specific cell-mediated and humoral responses using CAF01 were greater than those with currently used adjuvants.
Immune reconstitution inflammatory syndrome (IRIS) induced when patients with TB are treated with antiretroviral therapy has been attributed to dysregulated expansion of PPD-specific interferon- -secreting CD4⁺ T cells (9). Meintjes and coworkers performed longitudinal and cross-sectional studies of M. tuberculosis-specific ELISPOT responses and fluorescence activator cell sorter (FACS) analysis of blood cells from 129 patients with HIV-1-associated TB, 98 of whom received antiretroviral therapy (10). In a cross-sectional analysis, the frequency of interferon- -secreting T cells recognizing early secretory antigenic target (ESAT-6), -crystallins 1 and 2, and PPD of M. tuberculosis was higher in patients with IRIS than in patients treated for both HIV-1 and TB who did not develop IRIS (P 0.03). The biggest difference was in recognition of -crystallins. FACS analysis indicated equal proportions of CD4 and CD8 cells positive for the activation markers HLA-DR and CD-71 in both TB IRIS and non-IRIS patients. The percentage of CD4 cells positive for FOXP3 was low in both groups. Eight-week longitudinal analysis of patients with TB started on antiretroviral therapy showed dynamic changes in the numbers of antigen-specific interferon- -secreting T cells in both IRIS and non-IRIS groups, but the only significant trend was an increased response to PPD in the IRIS group (P = 0.041). Thus there is likely to be an association between Th1 cell expansion and IRIS, but the occurrence of similar expansion in the non-IRIS group brings into question whether these findings are causally related. It appears that further elucidation of the immunopathogenesis of IRIS is required.

EPIDEMIOLOGY OF TB AND NONTUBERCULOUS MYCOBACTERIAL DISEASE

In 1989, the United States embarked on an ambitious plan to eliminate TB nationwide (11). Although the incidence rates of TB have declined substantially in the United States, such disease cases represent only a tiny fraction of all TB infections. Thus, delineating national trends in infections would be of vital importance in anticipating future trends of TB. Khan and coworkers performed such a study on nationally representative cohorts of the United States noninstitutionalized civilian population participating in the 1971 to 1972 and 1990 to 2000 National Health and Nutrition Examination Surveys (12). Participants had tuberculin skin testing (TST), and the epidemiology of TB infection was compared across surveys. Logistic regression was used to identify associations between participant/household characteristics and TB infection. In 1999 to 2000, 4.2% of the United States population aged 1 year or older displayed evidence of TB infection. Among subjects aged 25 to 74, the prevalence of TB infection decreased from 14.4% in 1971 to 1972 to 5.6% in 1999 to 2000. Decline in the relative burden of infection among persons aged 25 to 74 was greater in the United States-born population (12.6-2.5%), than in the foreign-born population (35.9-21.3%). Thus, the prevalence of TB infection among the latter population is more than eight times that of the former population. This finding is most informative to healthcare policymakers in developing national TB control and elimination strategies.
Using the same United States database, Bennett and coworkers found higher prevalence of TB infection in the foreign born (18.7%), non-Hispanic blacks/African Americans (7.0%), Mexican Americans (9.4%), and individuals living in poverty (6.1%) (13). A total of 63% of the cases of latent TB infection (LTBI) were found among the foreign born. Among the United States born, after adjusting for confounders, LTBI was associated with non-Hispanic African American ethnicity, Mexican American ethnicity, and poverty. A total of 25.5% of persons with LTBI had been previously diagnosed as having LTBI or TB, and only 13.2% had been prescribed treatment. Thus, in addition to basic control measures for TB, elimination strategies should include targeted evaluation and treatment of individuals in high-prevalence groups, as well as enhanced support for global TB prevention and control.
TB contact tracing is an important component of TB control programs. Standardization of contact investigation protocols can improve efficiency. Thus, it would be relevant to develop models to select subjects for screening, especially in populations with high BCG vaccination rates (14). In a study designed for such a purpose, Aissa and coworkers developed a model for predicting the risk of TB infection among disease contacts through prospectively collecting standardized data on index TB cases and their contacts (15). The LTBI status was established using conventional TST, despite high BCG vaccination coverage. Eight independent risk factors were identified, including index characteristics of cavity and sputum smear with 100 or more acid-fast bacilli per field, and contact characteristics of age, active smoking, household contact at night, first-degree family relationship, birth in higher-incidence country, and free health care. The sensitivity, specificity, and the positive predictive value of this model with adjusted cutoffs were 0.93, 0.34, and 0.36, respectively, quite similar to those reported in other populations.
The model was also validated in a second prospective cohort of TB cases and their contacts, though of smaller size than the initial cohort (15). As a result of using the model, the number of TB contacts to be investigated could be reduced by 26%, while maintaining a false-negative rate of 8%, close to the background infection rate of the population. Thus, the study provides a standardized contact screening model that can reduce resources required, without negatively affecting TB control.
TST can produce false positive reactions when used in low-risk populations. Individuals in the U.S. Army who are deployed to areas of high TB prevalence are considered to be at high risk for TB infection, but in fact often have only limited contact with the local population. Mancuso and coworkers described the investigation of eight pseudoepidemics of TST conversions in U.S. Army populations, five of which were associated with overseas deployments (16). Initially reported risk of conversion in the outbreaks ranged from 1.3 to 15%. Repeat testing of converters (positives) found that 30 to 100% were negative on retesting. Several sources of false-positive results were identified in these pseudoepidemics, including variability in administration and reading of the test, variability in the product used for performance of the PPD, and cross-reacting immunologic response in the host arising from previous exposure to nontuberculous mycobacteria. As a result of these findings, U.S. Army forces appear, in general, to have a low risk for TB infection resulting from deployments due to limited exposure to local nationals with active TB, and universal testing in this population has a low positive predictive value.
Population-based studies in countries with low TB incidence have identified individual risk factors for clustering of patients with TB (17). However, predictors of further cluster growth have not been systematically assessed. Kik and coworkers evaluated these predictors through study of characteristics of the first two patients in TB clusters in The Netherlands (18). Assessment was restricted to cluster episodes of 2 years to only detect newly arising clusters. Those clusters comprising 2 to 4 cases and 5 or more cases were regarded as small and large episodes, respectively. Of 5,454 clustered cases, 32% were part of a cluster episode of 2 years. Of 622 cluster episodes, 54 (9%) were large and 568 (91%) were small episodes. Independent predictors for large episodes were: time interval of less than 3 months between diagnosis of the first two patients, both patients living in an urban area, and both patients originated from sub-Saharan Africa. The presence of such patient characteristics helps to provide early warning for cluster expansion and outbreak of TB and thus can prompt targeted intervention, especially intensified contact investigation.
Although diabetes mellitus has been known to be associated with risk of developing active TB, additional data on this association were considered to be desirable. Leung and coworkers assessed the effects of diabetes mellitus and diabetic control on the risk of TB after adjustment for sociodemographic and other background variables (19). Diabetes mellitus was found to be associated with a modest increase in the risk of active, culture-confirmed, and pulmonary TB, but not extrapulmonary TB (with or without pulmonary involvement), with adjusted hazard ratios (HRs) of 1.77, 1.91, 1.89, and 1.00, respectively. Diabetic subjects with hemoglobin A1c less than 7% at enrollment were not at increased risk. Among diabetic subjects, higher risks of active, culture-confirmed, and pulmonary (but not extrapulmonary) TB were observed with baseline hemoglobin A1c 7% or greater, with adjusted HRs of 3.11, 3.08, 3.63, and 0.77, respectively.
Pulmonary nontuberculous mycobacterial (PNTM) disease is increasing in prevalence, but the predisposing features have not been well described. Kim and coworkers prospectively studied 63 patients with PNTM disease, each of whom had computed tomography, echocardiography, pulmonary function testing, and flow cytometry of peripheral blood (20). In vitro cytokine production in response to mitogen and lipopolysaccharide was performed. Anthropometric measurements were compared with National Health and Nutrition Examination Survey age- and ethnicity-matched female control values extracted from the 2001 to 2002 data set. Patients were 59.9 ± 9.8 (mean ± SD) years old, and were 95% female and 68% lifetime nonsmokers. Forty-six were infected with Mycobacterium avium complex, Mycobacterium xenopi, or Mycobacterium kansasii; 17 were infected with rapidly growing mycobacteria. Female patients were significantly taller (164.7 cm vs. 161.0 cm, P < 0.001) and thinner (body mass index 21.1 vs. 28.2, P < 0.001) than matched National Health and Nutrition Examination Survey controls, and also were thinner (body mass index 21.1 vs. 26.8, P = 0.002) than patients with disseminated NTM disease. A total of 51% of patients had scoliosis, 11% pectus excavatum, and 9% mitral valve prolapse, all significantly higher percentages than in the reference population. Stimulated cytokine production was similar to healthy controls. CD4⁺, CD8⁺, B, and NK cell numbers were normal. A total of 36% of patients had mutations in the cystic fibrosis transmembrane conductance regulator gene. These findings are potentially useful in enhancing our understanding of the phenotypes and genotypes in PNTM disease.

DIAGNOSIS OF TB AND NONTUBERCULOUS MYCOBACTERIAL DISEASE

Although numerous studies have been published regarding the use of interferon- release assays (IGRAs) incorporating M. tuberculosis-specific antigens in the diagnosis of LTBI, their value in predicting the progression of latent infection to overt disease (i.e., active TB) needs to be established. Diel and coworkers compared the QuantiFERON-TB Gold Intube assay (QFT-GIT) with the TST in recently exposed close contacts of individuals with active TB (about 50% with BCG vaccination) regarding their performance in detecting development of active TB within 2 years (21). Among 601 contacts, 40.4% were TST positive and 11% QFT-GIT positive. IGRA positivity was associated with exposure time (P < 0.0001). Six contacts eventually progressed to develop disease. All six subjects were IGRA positive, and had refused preventive therapy for TB, giving a progression rate of 14.6% among those positive for QFT-GIT. The progression rate among untreated TST-positive subjects was significantly lower at 2.3% (P < 0.003). One subject who had progression to disease had a negative TST status. Thus, these data suggest that QFT-GIT screening determined more accurately LTBI than TST, and had at least equivalent sensitivity in predicting progression to TB disease. These findings may have significant health and economic implications in the enhancement of TB control.
The role of new T cell-based blood tests for diagnosis of active TB is not clear. Dosanjh and coworkers used TST, ELISPOT incorporating ESAT-6 and CFP-10, and ELISPOT(Plus) incorporating a novel antigen, Rv3879c, in evaluating 389 adults with high clinical suspicion of active TB (22). A total of 194 patients had active TB as a final diagnosis, with 79% culture-confirmed. Sensitivity for culture-positive and highly probable TB was 89% with ELISPOT(Plus), 85% with ELISPOT, 79% with 15-mm threshold TST, and 83% with stratified thresholds of 15 mm and 10 mm in vaccinated and unvaccinated patients, respectively. Thus, the ELISPOT(Plus) assay had 4% higher diagnostic sensitivity than ELISPOT, and was more sensitive than TST with a 15-mm cutoff point, but not with stratified cutoff points. The combined sensitivity of ELISPOT(Plus) and TST was 99%, conferring a negative likelihood ratio of 0.02 when both test results were negative. This approach might enable exclusion of active TB in patients with moderate to high pretest probability of disease. On the other hand, the ELISPOT(Plus), like the other tests, was not able to distinguish between active disease and latent infection. Its specificity for active disease was only 69%, even in presence of high clinical suspicion of active TB.
Higuchi and coworkers analyzed the relationship between results from QuantiFERON-TB Gold (QFT-G), a diagnostic tool for M. tuberculosis infection, and the risk of developing active TB (23). A total of 172 contacts of an infectious case of TB were evaluated for disease. Among them, 64.5% were QFT-G positive, and 22.7% had evidence of disease on chest radiograph and/or CT scan. Of these latter subjects, 89.7% were QFT-G positive. Statistically, the geometric mean of interferon- production levels of the active TB group was significantly higher than that present in the latent TB infection group (P = 0.013). A multivariate analysis showed that the combination of ESAT-6 and CFP-10 reactivity significantly enhanced the risk of TB disease among infected subjects.
Breen and coworkers performed a prospective evaluation, using a flow cytometric assay, to measure the percentage of interferon- -producing CD4⁺ lymphocytes after stimulation with M. tuberculosis PPD using bronchoalveolar lavage fluid from 250 sputum smear-negative patients with suspected TB (24). Of the individuals diagnosed with active TB, 106 of 111 (95%) had a positive immunoassay. In 139 individuals deemed not to have active TB, 105 (76%) were immunoassay negative. Of the remaining 34 subjects (24%) with a positive immunoassay, a substantial proportion had evidence of untreated TB; in 2 of these, active TB was subsequently diagnosed. Assay performance was not affected by HIV status, disease site, or BCG vaccination. In culture-positive pulmonary cases, response to PPD was more sensitive than nucleic acid amplification testing (94 vs. 73%). The use of ESAT-6 responses in 71 subjects was no better than PPD, and indeed 19% of those with culture-confirmed TB and a positive PPD immunoassay had no response to ESAT-6. Thus, these findings suggest that lung-orientated immunologic investigation is a potentially robust tool in diagnosis of sputum smear-negative active TB.
Serial monitoring of sputum microscopy for acid-fast bacilli to guide respiratory isolation of patients with suspected TB can result in expensive and unnecessary isolation, and may potentially lead to decreased vigilance in patients with compromised respiratory status. Campos and coworkers compared the performance of a single first-sputum M. tuberculosis-specific nucleic acid amplification (NAA) test to three sputum smears for assessing the need for respiratory isolation (25). In a prospective evaluation of 493 patients suspected of having TB, 46 (9.3%) had the diagnosis confirmed by culture. First-sputum NAA tests detected all TB patients who ultimately had a positive smear (n = 35), even when the first of the three specimens was smear negative. In addition, when compared with serial smears, the first-sputum NAA had a higher sensitivity (0.87; 95% confidence interval [CI], 0.74-0.95), and specificity (1.0) in detecting subjects with positive M. tuberculosis cultures, when compared with sputum smear: sensitivity (0.76; 95% CI, 0.61-0.87) and specificity (0.96; 95% CI, 0.94-0.98). Thus, a single first-sputum NAA can allow rapid and accurate identification of the subset of TB suspects who require respiratory isolation according to guidance from serial sputum smears.
The dual challenges of HIV infection and multidrug-resistant TB (MDR-TB) have posed significant problems in TB control, especially in South Africa. Conventional methods of drug susceptibility testing for M. tuberculosis require weeks to months before results are available. Barnard and coworkers assessed the performance and feasibility of implementation of a commercially available, molecular line-probe assay (GenoType MTBDRplus assay; Hain Life Sciences GmbH, Nephren, Germany) for rapid detection of rifampin and isoniazid resistance directly on 536 consecutive smear-positive sputum specimens from patients at high risk of MDR-TB in a busy routine diagnostic laboratory in Cape Town (26). Using this molecular tool, 97% of the smear-positive specimens gave interpretable results within 1 to 2 days. Sensitivity, specificity, and positive and negative predictive values were 98.9%, 99.4%, 97.9%, and 99.7%, respectively, for detection of rifampin resistance, and 94.2%, 99.7%, 99.1%, and 97.9% for detection of MDR, when conventional testing results were taken as reference standards. The molecular assay also performed well on specimens that were contaminated on conventional culture, and on smear-negative, culture-positive specimens. Thus, this highly accurate molecular tool, with its efficacy and cost effectiveness, may have the potential to revolutionize the diagnosis of MDR-TB.
A meta-analysis regarding GenoType MTBDR assays was performed by Ling and coworkers (27). It involved 14 comparisons for rifampin and 15 comparisons for isoniazid in 10 published articles. The pooled sensitivity (98.1%; 95% CI, 95.9-99.1) and specificity (98.7%; 95% CI, 97.3-99.4) for rifampin were high and consistent across all subgroups, assay versions, and specimen types. The sensitivity for isoniazid was lower (84.3%; 95% CI, 76.6-89.8), and less consistent than specificity (99.5%; 95% CI, 97.5-99.9). Furthermore, GenoType MTBDR assays have demonstrated excellent accuracy for rifampin resistance, even when used on clinical specimens.
Disseminated mycobacterial disease is an important cause of morbidity and mortality in patients with HIV infection. Nonspecific clinical presentation makes the diagnosis difficult. Santos and coworkers conducted a retrospective cohort study to compare the radiographic features of disseminated TB and nontuberculous mycobacterial disease in Brazil (28). Patients with nontuberculous mycobacterial disease had lower CD4 T-cell counts. Patients with TB had significantly more positive acid-fast smears. On chest radiograph, miliary infiltrates were only seen in patients with TB (28.1 vs. 0.0%; P = 0.01). Pleural effusion was seen more commonly in patients with TB (45.6 vs. 13.0%; P = 0.01). Abdominal adenopathy (73.1 vs. 33.3%; P = 0.003) and splenic hypoechoic nodules (38.5 vs. 0.0%; P = 0.002) were more common in patients with TB. Thus, these imaging features might help to distinguish the two types of mycobacterial diseases in HIV-infected patients with fever of unknown origin.
The diagnosis of pulmonary disease due to M. avium complex (MAC-PD) and/or its differentiation from pulmonary TB can be labor intensive and time consuming. This is largely due to the complicated criteria required, as in the American Thoracic Society guidelines (29), superimposed on the ubiquitous presence of MAC in the environment. In an attempt to overcome these difficulties, Kitada and coworkers developed an enzyme immunoassay for MAC-PD (30). This kit was aimed at detecting serum IgA antibody directed to the glycopeptidolipid core antigen specific for MAC. Among 70 patients with MAC-PD, 18 patients with MAC contamination, 37 patients with pulmonary TB, 45 patients with other lung diseases, and 76 healthy subjects, significantly higher serum IgA antibody levels were found in patients with MAC-PD than in the other groups (P < 0.0001). Setting the cutoff point at 0.7 U/ml resulted in a sensitivity and specificity of 84.3% and 100%, respectively, for diagnosing MAC-PD. Significantly higher antibody levels were also found in patients with nodular-bronchiectatic disease as compared with fibrocavitary disease (P < 0.05). There was a positive correlation between the extent of disease on chest computed tomography and the levels of antibody in patients with MAC-PD. This kit, if validated by studies involving larger patient populations in other areas, could prove useful clinically.

TREATMENT OF TB

As there is still inadequate information regarding the hepatotoxicity of pyrazinamide, Chang and coworkers compared continuation-phase regimens for treating TB that incorporated pyrazinamide, isoniazid, and/or rifampin with those containing isoniazid and rifampin to evaluate the hepatotoxicity of pyrazinamide (31). Cohort and nested case-control analyses were conducted on 3,007 patients with active TB. Cases included all patients with probable hepatotoxicity starting 12 weeks or more after treatment commencement. Hepatotoxicity was considered probable when serum alanine transaminase level exceeded three times the upper limit of normal. Treatment regimens for the 4 weeks preceding hepatotoxicity were compared with those of matched controls in comparable periods relative to the treatment commencement date. Hepatotoxicity occurred in 150 (5.0%) patients at any time, including 48 (1.6%) cases as defined above. From 12 weeks or more after starting treatment, the estimated risk of hepatotoxicity was 2.6% for regimens incorporating pyrazinamide, isoniazid, and/or rifampin, and 0.8% for standard regimens containing isoniazid and rifampin. Multivariable logistic analysis showed a significant association between hepatotoxicity and hepatitis B, previous hepatotoxicity, and treatment regimen. The adjusted odds ratio (95% CI) of hepatotoxicity for regimens incorporating pyrazinamide, isoniazid, and/or rifampin relative to standard regimens was 2.8 (1.4-5.9). Thus, adding pyrazinamide to isoniazid and rifampin increases the risk of hepatotoxicity appreciably.
MDR-TB poses an increasing challenge to TB control worldwide. In countries where drug susceptibility testing is not performed routinely, the current standardized regimens for treatment of TB may be contributing to the worsening drug resistance levels. Menzies and coworkers analyzed the association between estimated prevalence of initial or acquired MDR-TB and treatment outcome reported nationally (32). The data for these analyses came from the World Health Organization, the Joint United Nations Program on HIV/AIDS (UNAIDS), and the World Bank. Among countries using one of the two standardized initial regimens (2 mo rifampin/6 mo rifampin), failure rates averaged 5%, and relapse rates averaged 12.8% in 20 countries where the prevalence rate of initial MDR exceeded 3%, compared with an average of 1.6% (P < 0.0001) and 8.1% (P = 0.0002), respectively, in 83 countries where initial MDR prevalence rate was less than 3%. In 92 countries using a single standardized retreatment regimen, failure rates were 2.7%, 3.8%, 6.2%, and 8.1% in quartiles of increasing prevalence of acquired MDR (P < 0.0001). Thus, the currently recommended standardized initial and retreatment antituberculosis regimens should be reevaluated in countries where prevalence of initial MDR exceeds 3%, in light of poor treatment outcome of patients.
Extensively drug-resistant tuberculosis (XDR-TB) has emerged as a threat to public health globally in the recent years (33, 34). In an earlier report by Kwon and coworkers from South Korea regarding 155 patients with MDR-TB, 17% had XDR-TB (35). With the low prevalence of HIV infection in South Korea, all patients studied were not HIV-infected. The combined cure and treatment completion rate amounted to 66%. The treatment success rates did not differ significantly between patients with non-XDR MDR-TB and those with XDR-TB (66 vs. 67%). Surgical resection was performed more frequently for patients with XDR-TB than those with non-XDR MDR-TB (48 vs. 17%). Adjunctive surgical resection, body mass index 18.5 kg/m² or greater, use of more than 4 effective drugs, and negative sputum smear result were independent predictors of a favorable outcome.
Jeon and coworkers analyzed the risk factors and treatment outcomes among patients with XDR-TB at a tertiary referral hospital in South Korea (36). A total of 26 patients with XDR-TB were studied. Cumulative previous treatment duration (OR, 5.6; 95% CI, 1.0-59) and number of second-line anti-TB drugs previously received (OR, 1.3; 95% CI, 1.1-1.5) were significantly associated with the presence of XDR-TB in the crude analyses. After controlling for other factors in a multivariate model, cumulative previous treatment duration remained significantly associated with XDR-TB (OR, 5.8; 95% CI, 1.0-61). Patients with XDR-TB were more likely to produce culture-positive sputum at 6 months than patients with non-MDR-TB (risk ratio, 13). Kanamycin resistance was found to be predictive of 6-month culture positivity (risk ratio, 3.9) after adjustment for ofloxacin and streptomycin resistance.
A large cohort of patients in South Korea newly diagnosed with or retreated for MDR-TB were retrospectively studied by Kim and coworkers (37). The patients were largely HIV uninfected. Initial treatment outcomes and cumulative survival were analyzed, and predictors of treatment success and survival defined. Of 1,407 patients with MDR-TB, 5.3% had XDR-TB at treatment initiation. The default rate was quite high (32.2%). XDR-TB had lower treatment success (29.3 vs. 46.2%; P = 0.004), and higher all-cause (49.3 vs. 19.4%; P < 0.001) and TB-related mortality (41.3 vs. 11.8%; P < 0.001) than other non-XDR MDR-TB. The presence of XDR-TB significantly affected treatment success (OR, 0.23; P = 0.005), all-cause mortality (HR, 3.25; P < 0.001), and TB-related mortality (HR, 4.45; P < 0.001) on multivariate analysis. It is clear that adequate TB control policies should be implemented to prevent further development and spread of drug-resistant TB therein.
A study in Peru by Mitnick and coworkers described the management of XDR-TB and treatment outcomes among patients who were referred for individualized outpatient therapy (38). Of 651 patients tested for XDR-TB, 48 (7.4%) had the disease; the remaining 603 patients had MDR-TB. The patients with XDR-TB had undergone more treatment episodes than the other patients (mean ± SD number of regimens, 4.2 ± 1.9 vs. 3.2 ± 1.6; P < 0.001), and had isolates that were resistant to more drugs (8.4 ± 1.1 vs. 5.3 ± 1.5; P < 0.001). None of the patients with XDR-TB were coinfected with HIV. Patients with XDR-TB received daily, supervised therapy with an average of 5.3 ± 1.3 drugs, including cycloserine, an injectable drug, and a fluoroquinolone. Twenty-nine (60.4%) of these patients with XDR-TB completed treatment or were cured, as compared with 400 patients (66.3%) with MDR-TB.
Migliori and coworkers from Europe analyzed 240 MDR- and 48 XDR-TB cases (39). Among these cases, bacillary resistance to capreomycin in vitro yielded a higher proportion of failure and death than capreomycin-susceptible cases. Resistance to capreomycin was found to be independently associated with unfavorable outcome.
In an attempt to shorten the duration of current chemotherapy for TB and to treat MDR-TB (and XDR-TB) more effectively, new drugs are needed (40). Several novel interventions are currently under different phases of clinical development (41). One study demonstrated that combined substitutions of rifapentine for rifampin, and moxifloxacin for isoniazid, in the standard daily short-course regimen of rifampin, isoniazid, and pyrazinamide produced stable cure in 12 weeks or less in mouse models of TB (42). Rosenthal and coworkers further compared bactericidal activity and treatment-shortening potential between regimens consisting of isoniazid or moxifloxacin plus rifapentine and pyrazinamide administered either thrice weekly or daily using a similar model (43). After 4 weeks of treatment, daily and three-times weekly treatment with rifapentine, moxifloxacin, and pyrazinamide were significantly more active than that with rifapentine, isoniazid, and pyrazinamide. By 8 weeks of treatment, all mice receiving moxifloxacin-containing regimens were lung culture negative, whereas those mice receiving isoniazid-containing regimens continued to be lung culture positive. However, the duration of treatment necessary to achieve stable cure was 10 weeks for daily regimens and 12 weeks for thrice-weekly regimens, regardless of whether isoniazid or moxifloxacin was used. Thus, these results suggest that regimens consisting of isoniazid or moxifloxacin, plus rifapentine and pyrazinamide, may dramatically shorten the duration of treatment needed to cure TB.
Linezolid, an oxazolidinone, has been shown to have moderately potent antituberculosis activity against both drug-susceptible and drug-resistant disease (44, 45). However, the drug can produce serious toxicity, especially hematologic and neuronal, when administered for long periods. As a result, some clinicians tried dosing patients with MDR-TB at half of the usual dose of linezolid (i.e., 600 mg once daily instead of 600 mg twice daily) (46). Dietze and coworkers conducted a randomized open-label study using linezolid on patients with newly diagnosed smear-positive pulmonary TB (47). Thirty patients were assigned to receive isoniazid 300 mg once daily, linezolid 600 mg once daily, or linezolid 600 mg twice daily for 7 days. Sputum for quantitative culture was collected starting 2 days before and then daily during 7 days of study drug administration. Bactericidal activity was assessed by measuring the decline in bacillary load during the first 2 days (early bactericidal activity [EBA]) and last 5 days (extended EBA). The mean EBA of isoniazid (0.67 log₁₀ cfu/ml/d) was greater than that of linezolid twice and once daily (0.26 and 0.18 log₁₀ cfu/ml/d, respectively). The extended EBA of linezolid in the last 5 days was minimal. It was thus concluded that linezolid has moderate EBA against rapidly dividing tubercle bacilli in patients with cavitary TB but little extended EBA. The sterilizing capacity of the drug requires further delineation.
Louie and coworkers explored the use of an in vitro pharmacodynamic model and Monte Carlo simulation to derive a linezolid regimen that could optimize bacterial kill and prevent emergence of resistance in Bacillus anthracis (48). They concluded that the once-daily pharmacodynamically optimized regimen for linezolid could achieve these purposes. The lower daily dosage of the optimized regimen might decrease drug toxicity and improve patient adherence. These data may have potential therapeutic implications, especially regarding infections requiring a long duration of linezolid treatment.
R207910 is a diarylquinoline with novel activity on ATP synthase of M. tuberculosis resulting in great potency against TB in murine models (49). Lounis and coworkers assessed the impact of reducing the dose of R207910 on efficacy when R207910 was combined with a background regimen of isoniazid, rifampin, and pyrazinamide (50). Addition of 25 mg/kg or 12.5 mg/kg R207910 to the background regimen resulted in faster mycobacterial clearance and culture negativity. The difference in efficacy between the two doses was not statistically significant. The minimum bactericidal dose of R207910 when tested as combination therapy was identical to that when tested in monotherapy. Because of drug-drug interactions in human subjects, the activity of R207910 could be less than that expected from mouse studies. These data in the mouse model demonstrated that R207910 has significant activity even when exposure was reduced by 50%, and when added to a strong background regimen of isoniazid, rifampin, and pyrazinamide.
Rustomjee and coworkers performed a study regarding the early bactericidal activity and pharmacokinetics of the diarylquinoline TMC207 (R207910) in treatment of pulmonary TB (51). The study lasted 7 days. Significant bactericidal activity of TMC207 was observed from day 4 onward, and was similar in magnitude to that of isoniazid and rifampin over the same period. The pharmacokinetics of the diarylquinoline were linear across the dose range. Above all, TMC207 given at a dose of 400 mg once daily was well tolerated, without occurrence of drug-related serious adverse events.
As R207910 (TMC207), a diarylquinoline with potent antituberculosis activity, has a long half-life (more than 2 d in the mouse) (49), it might be a good candidate for combination therapy with rifapentine in TB. Veziris and coworkers evaluated the activity of once-weekly R207910 monotherapy and combinations of R207910 with isoniazid, rifapentine, moxifloxacin, and pyrazinamide in a murine model of TB (52). Eight weeks of monotherapy reduced the bacillary load by 3 to 4 log₁₀ for rifapentine, and by 5 to 6 log₁₀ for R207910 (P < 0.05). The addition of rifapentine and isoniazid or moxifloxacin did not improve the bactericidal activity of R207910 monotherapy. In contrast, the triple combination R207910 + rifapentine + pyrazinamide given once weekly during 2 months was significantly more active than R207910 monotherapy or other R207910 combinations, as well as the current standard regimen of rifampin + isoniazid + pyrazinamide given five times per week. Thus R207910 + rifapentine + pyrazinamide might constitute a potent once-weekly regimen for treatment of TB. An accompanying editorial to this study reiterated the importance of obtaining further data regarding the prevention of TB relapse and suppression of development of bacillary resistance to R207910 (53). Furthermore, as both R207910 and rifapentine are metabolized by the cytochrome P450 enzymes, induction of enzymes by rifamycin might accelerate the metabolism of the diarylquinoline resulting in attenuation of its therapeutic efficacy.
A recent study in murine TB by Tasneen and coworkers explored the possible enhancement of bactericidal activity of rifampin and/or pyrazinamide when combined with PA-824 (54). It was found that the combination of the rifamycin, PA-824, and pyrazinamide rendered all mice culture negative after 2 months of treatment, and free of relapse after 4 months of treatment, whereas some mice receiving rifampin, isoniazid, and pyrazinamide remained culture positive and 15% relapsed after completing 4 months of therapy. These results support the evaluation of regimens based on rifampin + PA-824 + pyrazinamide combination in phase II clinical trials.
Nuermberger and coworkers demonstrated that the novel combination of PA-824, moxifloxacin, and pyrazinamide cured mice more rapidly than the first-line regimen of rifampin, isoniazid, and pyrazinamide (55). If this is applicable to humans, such drug combination might potentially shorten the duration of MDR-TB.

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Urinary Adiponectin Excretion: A Novel Marker for Vascular Damage in Type 2 Diabetes

Maximilian von Eynatten; Dan Liu; Cornelia Hock; Dimitrios Oikonomou; Marcus Baumann; Bruno Allolio; Grigorios Korosoglou; Michael Morcos; Valentina Campean; Kerstin Amann; Jens Lutz; Uwe Heemann; Peter P. Nawroth; Angelika Bierhaus; Per M. Humpert

                                                                                                    Diabetes. 2009;58(9):2093-2099. 

Abstract

Objective Markers reliably identifying vascular damage and risk in diabetic patients are rare, and reports on associations of serum adiponectin with macrovascular disease have been inconsistent. In contrast to existing data on serum adiponectin, this study assesses whether urinary adiponectin excretion might represent a more consistent vascular damage marker in type 2 diabetes.
Research design and methods Adiponectin distribution in human kidney biopsies was assessed by immunohistochemistry, and urinary adiponectin isoforms were characterized by Western blot analysis. Total urinary adiponectin excretion rate was measured in 156 patients with type 2 diabetes who had a history of diabetic nephropathy and 40 healthy control subjects using enzyme-linked immunosorbent assay. Atherosclerotic burden was assessed by common carotid artery intima-media-thickness (IMT).
Results A homogenous staining of adiponectin was found on the endothelial surface of glomerular capillaries and intrarenal arterioles in nondiabetic kidneys, whereas staining was decreased in diabetic nephropathy. Low-molecular adiponectin isoforms (~30-70 kDa) were detected in urine by Western blot analysis. Urinary adiponectin was significantly increased in type 2 diabetes (7.68 ± 14.26 vs. control subjects: 2.91 ± 3.85 μg/g creatinine, P = 0.008). Among type 2 diabetic patients, adiponectinuria was associated with IMT (r = 0.479, P < 0.001) and proved to be a powerful independent predictor of IMT (β = 0.360, P < 0.001) in multivariable regression analyses. In a risk prediction model including variables of the UK Prospective Diabetes Study coronary heart disease risk engine urinary adiponectin, but not the albumin excretion rate, added significant value for the prediction of increased IMT (P = 0.007).
Conclusions Quantification of urinary adiponectin excretion appears to be an independent indicator of vascular damage potentially identifying an increased risk for vascular events.

Introduction

Cardiovascular disease (CVD) is the leading cause of mortality in patients with type 2 diabetes, and the identification of individual risk patterns is fundamental for the prevention and treatment of CVD. However, risk stratification in patients with diabetes is still vague,^[1,2] and, consequently, numbers needed to treat for prevention of a single cardiovascular event in clinical trials are ~100-200 patients per year.^[3-5]
Most of the recently described risk markers are metabolic or inflammatory molecules that do not directly indicate vascular damage. Therefore, these indirect markers show variations in risk prediction depending on the metabolic status of the study group.^[6,7] This becomes evident reviewing data on serum adiponectin; whereas low-circulating adiponectin was significantly associated with increased primary CVD risk in apparently healthy men,^[8] subsequent studies in high-risk populations, as well as patients with prevalent coronary heart disease (CHD), failed to confirm this association.^[9,10] A reason for this discrepancy between different groups of risk patients could be a reverse causality, where silent or apparent CVD might lead to compensatory rises in serum adiponectin. Consistently, it was shown in type 2 diabetic patients that adiponectin is lowest in the presence of impaired glucose regulation and early diabetes, whereas long diabetes duration is associated with a significant increase in circulating adiponectin.^[11]
Adiponectin is a 30-kDa adipocyte-derived vasoactive peptide closely linked to components of the metabolic syndrome (rev. in [12]). It has anti-inflammatory and antiatherosclerotic properties on endothelial cells by decreasing vascular inflammation, foam cell formation, and cell adhesion, which all are involved in the initiation and progression of vascular lesions.^[12] Recently, it was reported that adiponectin has a distinct role for glomerular homeostasis in an experimental model.^[13] Hence, adiponectin could be present on human renal endothelium and glomerular capillary stress in diabetes may promote shedding of adiponectin from endothelial surfaces by proteolytic cleavage, causing degradation of high-order complexes of adiponectin and subsequent appearance of the adiponectin monomer (~28 kDa), dimer (~56 kDa), and trimer (~68 kDa) in urine.
We hypothesized that adiponectin appears in urine consequently reflecting early glomerular vascular damage in type 2 diabetes rather than the metabolic changes associated with serum adiponectin. To characterize a possible diagnostic value of urinary adiponectin excretion, patients with type 2 diabetes and early diabetic nephropathy (i.e., a history of microalbuminuria) were studied, and the atherosclerotic burden of these patients was assessed by quantification of common carotid artery intima-media-thickness (IMT). Both urinary adiponectin and urinary albumin excretion rate (AER) as an established marker of micro- and macrovascular dysfunction in type 2 diabetes were evaluated for the prediction of increased IMT in comparative analyses

Study Population and Data Collection

Patients (156) with type 2 diabetes, according to the American Diabetes Association (ADA) criteria,^[14] were recruited from family practices being referred to the diabetes outpatient clinic at the University Hospital Heidelberg for specialist treatment. For eligibility, patients had to have a documented history of microalbuminuria in at least two separate urine samples [albumin creatinine ratio (ACR) >30 mg/g creatinine or AER >30 mg/24h]. Healthy control subjects (40) were recruited at the outpatient clinic of the University Hospital Wuerzburg. In the latter, manifest CVD and/or diabetes, fasting plasma glucose (FPG) level ≥7 mmol/l, acute or chronic kidney disease, present microalbuminuria, history of hypertension and/or lipid disorder, and intake of any regular medication was an exclusion criterion. Detailed patient characteristics are shown in Table 1. In all individuals, 24-h urine samples were collected on 3 consecutive days and the mean of AER and of the creatinine clearance was taken for statistical evaluation. All blood values, as well as ambulatory 24-h blood pressure values (given as mean of 24 h), were taken on day 1. The study complied with the Declaration of Helsinki, and all subjects gave written informed consent. The study was approved by the ethics committees of the Universities of Heidelberg and Wuerzbur

Adiponectin Immunohistochemistry in Human Kidneys

Immunohistochemical analyses were performed in human kidney biopsies from type 2 diabetic patients (n = 6) and tumor-distant kidney tissues from nondiabetic patients after tumornephrectomy (n = 6). Early diabetic nephropathy (n = 3) was classified as presenting with micro- or macroalbuminuria and calculated glomerular filtration rate >60 ml/min. Indication for kidney biopsy was based on progressive increase in proteinuria >1 g/24 h in two subjects and progressive increase in serum creatinine in one. Late diabetic nephropathy (n = 3) was classified by micro- or macroalbuminuria and calculated glomerular filtration rate <30 ml/min. Indication for kidney biopsy in these patients was progressive nephrotic proteinuria. In nondiabetic control subjects, tumor-distant kidney tissue was embedded in paraffin blocks and according histological samples were qualified to show normal kidney morphology by two independent experts. Utilization of noncancerous regions of resected kidneys distant from the tumor as control tissue has previously been reported.^[15,16] None of these patients had an FPG level ≥7 mmol/l or present microalbuminuria. Immunohistochemical staining was performed on 3-μm sections of formaldehyde-fixed and paraffin-embedded tissue using the avidin-biotin complex method. Tissues were deparaffinized with xylene and rehydrated through graded concentrations of ethanol. After rehydration, the sections were pretreated by microwave heating in citrate buffer (pH 6.0) for 20 min. The primary antibody against adiponectin (Adiponectin/Acrp30 biotinylated affinity purified polyclonal antibody) was obtained from R&D Systems (Minneapolis, MN) and used at a dilution of 1:25 for 2 h at room temperature, followed by incubation with horseradish peroxidase-labeled streptavidin (Vector Laboratories, Burlingame, CA) diluted 1:200 for 1 h. NovaRED (Vector) was applied for visualization. Control subjects, omitting the first antibody for each paraffin block tested, were negative

Detection and Characterization of Adiponectin Multimers in Urine by Western Blot

SDS-PAGE was performed after modification of the protocol as previously described.^[17] Urinary samples (16 μl) were mixed with SDS-sample buffer and then incubated at room temperature for 1 h. Urinary proteins were separated by 10% SDS-PAGE, and transferred to a nitrocellulose membrane. Membranes were blocked with Tris-buffered saline Tween-5% skim milk and then incubated with a goat anti-human adiponectin polyclonal antibody (1:200; R&D Systems, Wiesbaden, Germany) for 1 h at room temperature. After washing (three times for 5 min), membranes were incubated with horseradish peroxidase-conjugated donkey anti-goat antibody (1:3,200; Santa Cruz Biotechnology, Heidelberg, Germany) for 1 h at room temperature and then washed thoroughly (three times for 5 min). Signals were visualized using lumi-light Western blotting substrate (Roche Diagnostics, Mannheim, Germany) and the image was acquired by Kodak IS440CF Imaging Station. Specificity of bands was shown in a competition experiment. In competition experiments, membranes were preincubated overnight with 2 μg/ml recombinant human adiponectin (R&D Systems) as a competitor before Western blotting.

Clinical Chemistry

Blood was drawn on day 1 in a fasting state under standardized conditions and stored at -80°C until analysis. Total urinary adiponectin concentrations were measured in duplicates by a high-sensitive enzyme-linked immunosorbent assay (ELISA; BioVendor, Brno, Czech Republic) according to the manufacturer's protocol. The intra- and interassay variations were 5.4 and 9.0%, respectively. Urinary adiponectin levels (nanogram per milliliter) were adjusted for urinary creatinine excretion and expressed as micrograms per gram of creatinine for statistical analysis. In type 2 diabetic patients, presence of adiponectinuria was defined as level >mean + 2 SD (95. percentile) of the adiponectin excretion rate in healthy control subjects (→urinary adiponectin >10.61 μg/g creatinine). FPG was measured by a glucose oxidase method. Triglyceride, total cholesterol, and HDL cholesterol levels were quantified by standard laboratory methods, and LDL cholesterol levels were calculated by using the Friedewald formula. A1C was measured by high-performance liquid chromatography on a Variant II device (Bio-Rad Laboratories, Munich, Germany). Cystatin C was measured by ELISA (BioVendor, Brno, Czech Republic), and high-sensitive C-reactive protein (hsCRP) levels were determined by nephelometry (Dade Behring, Cupertino, CA). AER was assessed and performed in three consecutive 24-h urinary collections. For collection of the urine sample, a 3-l plastic container was used, and the volume of urine was measured to the nearest 50 ml. Urine aliquots were stored deep frozen at -80°C until analyses. Albumin levels were determined by turbidimetry (Siemens Healthcare Diagnostics, Eschborn, Germany). AER was expressed as milligrams per 24 h. Patients with an AER of 30-300 mg/24 h were defined to have microalbuminuria and an AER >300 mg/24 h was defined as macroalbuminuria

Assessment of Carotid Atherosclerosis

IMT was detected using high-resolution B-mode ultrasound (Voluson 730 Kretz, Tiefenbach, Austria) of the extracranial carotid arteries bilaterally under continuous detection of the heart cycle using a three-lead electrocardiogram. The whole imaging and quantification procedure was performed digitally (Voluson 730 Kretz, Tiefenbach, Austria) at the time of study entry by a single investigator blinded for clinical data. For the purpose of this study, IMTs of the far wall of the common carotid artery were detected in end-diastolic frames, ~10 mm proximal to the carotid bulb, according to a previously described scanning protocol.^[18] The measurements were performed in four points of both common carotid arteries avoiding areas of atherosclerotic plaque formation. The mean of the resulting eight single measurements was taken as mean IMT for statistical analyses in this study.

Statistical Analyses

Statistical analyses were performed using SPSS software version 15.0 (SPSS, Chicago, IL). Spearman correlation coefficients were used to describe the association between urinary adiponectin and the variables of interest. Comparison between two sets of patients was performed by independent t test or Mann-Whitney U test. Multivariable linear regression analyses evaluated the association of urinary adiponectin with IMT. The models fitted for IMT as a dependent variable, included age, sex, waist-to-hip ratio (WHR), HDL, LDL, hsCRP, A1C, AER, smoking status, mean arterial pressure (MAP), diabetes duration, serum, and urinary adiponectin concentrations. The UK Prospective Diabetes Study (UKPDS) risk engine was previously introduced as a parametric model that provides the estimates of primary coronary heart disease (CHD) risk in type 2 diabetes.^[19] In contrast to previous models for CHD, such as the Framingham risk equations, the diabetes-specific approach of the UKPDS risk engine includes A1C as continuous variable. Age as a risk factor is replaced by two diabetes-specific variables: age at diagnosis of type 2 diabetes and time since diagnosis. Furthermore, as there is evidence that diabetic dyslipidemia is qualitatively different from dyslipidemia in the general population, total and HDL cholesterol are included instead of LDL cholesterol. The complete model incorporates age at diagnosis of diabetes, diabetes duration, sex, smoking status, A1C values, systolic blood pressure, and the total and/or HDL cholesterol ratio.^[19] We plotted receiver operating characteristic (ROC) curves and the area under the curve (AUC) was analyzed to study the value of the UKPDS CHD risk engine for the prediction of carotid atherosclerosis (upper vs. lower two tertiles of IMT). Calculations were performed using online provided software (http://www.dtu.ox.ac.uk). Intertertile cutoff points of IMT were <0.82 mm (n = 52), 0.82-0.94 mm (n = 52), and >0.94 mm (n = 52). Values for the AUC as obtained by the UKPDS risk engine were compared with the AUC after additional inclusion of AER and urinary adiponectin. Statistical comparisons of the AUC ROC curves were performed using "roccomp" command provided by the statistical software Stata/SE 8.2 for Windows (Stata Corporation, College Station, TX). P < 0.05 was considered to be statistically significant.

 Results

Immunohistochemistry of Adiponectin in Human Kidneys and Determination of Urinary Adiponectin Isoforms by Western Blot

A strong staining for adiponectin was detected on the endothelium of intrarenal arteries/arterioles and on the endothelial surface of glomerular and peritubular capillaries in all nondiabetic kidneys, and representive findings are shown in Fig. 1A. In patients with early diabetic nephropathy, the homogeneous glomerular staining pattern of adiponectin was markedly decreased, whereas adiponectin staining in intrarenal arteries/arterioles remained unchanged  In type 2 diabetic kidney biopsies, adiponectin was found in tubular casts, indicating urinary excretion of the protein  In patients at advanced stages of diabetic nephropathy with overt glomerulosclerosis, glomerular staining for adiponectin was almost completely lost
Next, we studied whether adiponectin is specifically detectable in urine of patients with diabetic nephropathy and either current normoalbuminuria or microalbuminuria and healthy control subjects and whether different isoforms of adiponectin are present in these samples. In Western blot analyses of urine samples from patients with diabetic nephropathy, the strongest signals were found at ~75 kDa, most likely representing the low-molecular weight adiponectin trimer (68 kDa). An additional signal at ~25 kDa represents the adiponectin monomer (28 kDa) as previously shown for serum adiponectin.^[17] In healthy control subjects, antigens representing adiponectin dimers (56 kDa) and monomers were found; however, overall intensity of these signals was much lower compared with the diabetic patients studied

Association of Serum and Urinary Adiponectin Levels with Cardiovascular Risk Factors

Serum adiponectin was significantly lower and urinary adiponectin levels significantly higher in patients with type 2 diabetes than in control subjects (mean serum adiponectin: 7.0 ± 4.9 vs. 10.3 ± 6.6 μg/ml, P = 0.033; mean urinary adiponectin: 7.68 ± 14.26 vs. 2.91 ± 3.85 μg/g creatinine, P = 0.008; Fig. 1E). Type 2 diabetic patients were more often men, nonsmokers, and had higher age, BMI and WHR compared with control subjects. As would be expected, type 2 diabetes was associated with significantly increased values of traditional cardiovascular risk factors, such as LDL, triglycerides, systolic and diastolic blood pressure, MAP, FPG, A1C, and hsCRP values. Kidney function was not significantly different between the two groups (type 2 diabetes, creatinine clearance: 109.6 ± 40.7 vs. control subjects: 119.3 ± 41.2 ml/min, P = 0.146), whereas serum cystatin C levels and levels of albuminuria were significantly higher in patients with type 2 diabetes than in control subjects, reflecting the early functional alterations in diabetic nephropathy (mean cystatin C: 0.79 ± 0.31 vs. 0.57 ± 0.13 mg/l, P < 0.001; median AER: 43.9 [21.5-103.1] vs. <10 mg/24 h, P < 0.001;. Bivariate correlations showed significant associations between serum adiponectin and sex, age, WHR, HDL, triglycerides, FPG, creatinine clearance, and hsCRP in patients with type 2 diabetes. For urinary adiponectin, there were no significant correlations with components of the metabolic syndrome like blood lipids or WHR, yet there were significant associations with increased age, duration of diabetes, and patients treated with ACE inhibitors or angiotensin receptor blockers.
Twenty-one (13.5%) of the participants with type 2 diabetes were found to have increased urinary adiponectin but no current albuminuria This subgroup of patients did not differ significantly from patients without adiponectinuria (group 1) or current albuminuria (group 3) with respect to age, glycemic control, and renal function. However, individuals in this group had significantly increased IMT compared with patients without adiponectinuria (0.95 ± 0.10 vs. 0.84 ± 0.14 mm; P < 0.001) and patients with current albuminuria (0.95 ± 0.10 vs. 0.89 ± 0.15 mm; P < 0.05), although the latter had longer diabetes duration (13.6 [7.0-18.6] vs. 9.5 [5.8-17.3] years: P < 0.05) and increased FPG levels (8.67 ± 2.97 vs. 6.94 ± 2.67 mmol/l; P < 0.01)

Associations of Carotid Atherosclerosis with Urinary and Serum Adiponectin and Other CVD Risk Factors in Patients with Type 2 Diabetes

In bivariate correlation analysis IMT was significantly and positively associated with urinary adiponectin (r = 0.479, P < 0.001) and negatively associated with serum adiponectin levels (r = -0.202, P = 0.017). Among other cardiovascular risk factors, age (r = 0.277, P = 0.001), diabetes duration (r = 0.227, P = 0.007), systolic blood pressure (r = 0.171, P = 0.048), and LDL cholesterol (r = 0.212, P = 0.012) were significantly associated with IMT.
In multivariable linear regression analyses with IMT as dependent variable, age (β = 0.239, P = 0.012), LDL cholesterol (β = 0.231, P = 0.009), and diabetes duration (β = 0.197, P = 0.026) were independently associated with the extent of carotid atherosclerosis. Urinary adiponectin had the strongest association with IMT in this model (β = 0.360, P < 0.001). We performed subgroup analyses investigating a potential linear relationship between urinary adiponectin and IMT, and patients were divided into quartiles of increasing urinary adiponectin. A stepwise increase in urinary adiponectin was associated with increased IMT (urinary adiponectin <1.05 μg/g creatinine: IMT mean [95% CI] 0.79 (0.75-0.83) mm; urinary adiponectin 1.05-1.89 μg/g creatinine: IMT 0.85 (0.80-0.91) mm; urinary adiponectin 1.90-7.20 μg/g creatinine: IMT 0.89 (0.85-0.93) mm; urinary adiponectin >7.20 μg/g creatinine: IMT 0.98 (0.95-1.02) mm; P < 0.001 by ANOVA;.

Predictive Value of Urinary Adiponectin in Comparison with Urinary Albumin for Extent of Carotid Atherosclerosis

We performed ROC analyses in models including traditional cardiovascular risk factors adding AER and urinary adiponectin levels to quantify their power for the prediction of carotid IMT (upper vs. lower two tertiles) in patients with type 2 diabetes. Carotid IMT as well as the UKPDS CHD risk engine have previously been shown to predict CVD risk in patients with type 2 diabetes;^[19] in this study, the UKPDS CHD risk engine score and IMT were significantly correlated (r = 0.509, P < 0.001). Therefore, the risk factors represented in the UKPDS CHD risk engine (age at diabetes diagnosis, diabetes duration, sex, smoking status, systolic blood pressure, A1C, and total and HDL cholesterol) were chosen in a basis model for ROC analysis. The UKPDS CHD risk engine factors reached an AUC of 0.700 (95% CI 0.607-0.792, ). Although urinary albumin levels were significantly associated with IMT in bivariate analysis (r = 0.202, P < 0.010), further addition of AER to the basis model did not significantly alter the predictive value for carotid IMT (AUC 0.702 [95% CI 0.610-0.795], ). Inclusion of urinary adiponectin added significant predictive value for prediction of IMT compared with the basis model of the UKPDS CHD risk engine factors (AUC 0.800 [95% CI 0.724-0.872], P = 0.007,).

Discussion

This is the first study evaluating urinary adiponectin as a novel marker for vascular damage. The results of this study imply that urinary adiponectin may emerge as a pathophysiologically plausible and valuable marker for prevalent micro- and macrovascular disease in type 2 diabetes.
The American guidelines recommend an office-based assessment as the initial step in predicting CVD risk in primary prevention utilizing multifactorial statistical models.^[20] However, a certain proportion of patients will be misclassified using this traditional risk prediction, and CVD risk has particularly been underestimated in patients with diabetes.^[21] Apart from albuminuria, atherogenic dyslipidemia and to a lesser extent long-term glucose control (that are included in the UKPDS risk engine), novel biochemical risk markers were found to be of minor importance for the overall prediction of CVD risk.^[2,6,7]
In this study, urinary adiponectin was superior to AER in the prediction of increased IMT. Measurement of urinary albumin excretion is currently utilized as a screening test for the presence of diabetes-related kidney disease. Furthermore, microalbuminuria is a marker of endothelial dysfunction and predicts CVD in patients with type 2 diabetes.^[22,23] However, risk prediction by assessment of urinary albumin levels reveals some important limitations. A diabetes duration of >6 years may precede the first appearance of urinary albumin,^[24] and vascular changes start long before the first appearance of albumin in urine and even before the diagnosis of diabetes.^[25,26] Hence, closing this diagnostic gap is highly desired. In this study, 13.5% of the type 2 diabetic patients were shown to have a significant adiponectinuria without current albuminuria. Despite similar age and glycemic control, this subgroup of patients had a significantly increased IMT compared with participants without adiponectinuria or current albuminuria (Table 2). In accordance with the hypothesis, this implies that adiponectinuria could be an early marker of endothelial damage on a prealbuminuric level and that urinary adiponectin has the potential to exceed the predictive value of urinary albumin for CVD risk evaluation. However, although Table 2 shows significant differences between groups 2 and 3, the subgroup of patients with adiponectinuria only (group 2) is small and differences between the two groups will have to be studied in larger cohorts. One possible explanation for the superiority of urinary adiponectin compared with urinary albumin for prediction of increased IMT in this study could be originated from previously published experimental and clinical data. The prevalence of microalbuminuria in patients with type 2 diabetes is estimated at about 20%, and about 30% in those subjects >55 years of age.^[27] Hence, it appears that applicability of microalbuminuria for CVD risk evaluation in type 2 diabetes per se is limited. Moreover, in large prospective cohort studies, the increased risk for CVD started from urinary albumin levels well below the cutoff for micoalbuminuria,^[25] and, thus, a considerable percentage of high-risk patients will be missed by screening for albuminuria utilizing current cut off values. This has recently been supported by data in the Finnish Diabetic Nephropathy (FinnDiane) Study, in which a significant number of type 1 diabetic patients at high risk for premature death had normoalbuminuria.^[28]
The association between IMT and urinary adiponectin shown here was independent of circulating adiponectin levels. Moreover, urinary adiponectin levels did not significantly correlate with most of the traditional cardiovascular risk factors in bivariate analyses. This is an advantageous precondition to achieve significant additional value in risk prediction models. Although serum adiponectin is strongly associated with the components of the metabolic syndrome and closely linked to metabolic risk factors like WHR, HDL cholesterol, and triglycerides, urinary adiponectin seems to indicate vascular damage and is therefore associated with older age and duration of type 2 diabetes in this study.
The finding of extensive staining for adiponectin in control kidneys, lining glomerular capillaries, and intrarenal arterioles was somehow unexpected, because in rodents, adiponectin accumulation could only be detected in injured vessels.^[29] Although histological examination of tumor distant regions from resected kidney tissue, serving as "healthy" control deserves cautious interpretation our data indicate that binding of adiponectin to the glomerular endothelium could be essential for kidney homeostasis. This idea is further supported by two independent experimental studies^[13,30] in which adiponectin-deficient (Adip^-/-) mice treated with adiponectin showed a reduction of albuminuria, improvement of podocyte function, and decreased urinary and glomerular markers of oxidant stress. Thus, we speculate that the ubiquitous distribution of adiponectin in nondiabetic glomerular capillaries in this study and its subsequently increasing appearance in urine, associated with loss of glomerular adiponectin in diabetic nephropathy, might reflect earlier vascular damage than the vascular leakage detected by albuminuria. On the other hand, adiponectin was still present at the endothelial surface of intrarenal arterioles in patients with diabetic nephropathy that may be because of different functions of adiponectin in these tissues.^[13,29,30] The role of adiponectin in the human glomerulum needs to be addressed in future studies because its excretion could be a more pathophysiological marker of vascular stress and may precede the onset of microalbuminuria and renal failure in type 2 diabetes. Consistent with this hypothesis, we found a significant lower accumulation of adiponectin in glomerular capillaries of patients with type 2 diabetes. This could reflect an increased urinary loss of the adipokine and might be explained by damage to the glomerular capillary wall resulting in a significant loss of endothelial binding sites for adiponectin.
We recognize the limitations of the present study. The cross-sectional design of our study warrants cautious interpretation of the results, and further investigations in large prospective trials with defined CVD end points are necessary to substantiate these findings. As all patients of our study were selected by a previous history of microalbuminuria, future studies will have to address whether the proposed association between urinary adiponectin and atherosclerosis can be confirmed in patients at advanced stages of diabetic nephropathy, as well as in nonalbuminuric diabetic patients. Conclusions can only be drawn for the high-risk group of type 2 diabetic patients in this study. Moreover, because the number of histological samples examined in this study is low, additional studies are clearly needed to further elucidate the distribution pattern of glomerular adiponectin in different renal pathologies to substantiate the potential role of adiponectin for glomerular homeostasis in humans.
In conclusion, measurement of urinary adiponectin may emerge as a novel and easy-to-obtain method for the clinical assessment of vascular stress and CVD risk in type 2 diabetes that needs to be validated in larger prospective studies and different samples including diabetic patients without a history of microalbuminuria.

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• 28. Mäkinen VP, Forsblom C, Thorn LM, Wadén J, Gordin D, Heikkilä O, Hietala K, Kyllönen L, Kytö J, Rosengård-Bärlund M, Saraheimo M, Tolonen N, Parkkonen M, Kaski K, Ala-Korpela M, Groop PH : the FinnDiane Study Group. Metabolic phenotypes, vascular complications, and premature deaths in a population of 4,197 patients with type 1 diabetes. Diabetes 2008; 57: 2480-2487
• 29. Okamoto Y, Arita Y, Nishida M, Muraguchi M, Ouchi N, Takahashi M, Igura T, Inui Y, Kihara S, Nakamura T, Yamashita S, Miyagawa J, Funahashi T, Matsuzawa Y : An adipocyte-derived plasma protein, adiponectin, adheres to injured vascular walls. Horm Metab Res 2000; 32: 47-50
• 30. Ohashi K, Iwatani H, Kihara S, Nakagawa Y, Komura N, Fujita K, Maeda N, Nishida M, Katsube F, Shimomura I, Ito T, Funahashi T : Exacerbation of albuminuria and renal fibrosis in subtotal renal ablation model of adiponectin-knockout mice. Arterioscler Thromb Vasc Biol 2007; 27: 1910-1917

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Comparison of Two Red-cell Transfusion Strategies after Pediatric Cardiac Surgery: A Subgroup Analysis

Ariane Willems, MD; Karen Harrington, MD; Jacques Lacroix, MD; Dominique Biarent, MD; Ari R. Joffe, MD; David Wensley, MD; Thierry Ducruet, MSc; Paul C. Hébert, MD; Marisa Tucci, MD

                                                                                           Crit Care Med. 2010;38(2):649-656

Abstract

Objective: To determine the impact of a restrictive vs. a liberal transfusion strategy on new or progressive multiple organ dysfunction syndrome in children post cardiac surgery. The optimal transfusion threshold after cardiac surgery in children is unknown.
Design: Randomized, controlled trial.
Setting: Tertiary pediatric intensive care units.
Patients: Participants are a subgroup of pediatric patients post cardiac surgery from the TRIPICU (Transfusion Requirements in Pediatric Intensive Care Units) study. Exclusion criteria specific to the cardiac surgery subgroup included: age < 28 days and patients remaining cyanotic.
Intervention: Critically ill children with a hemoglobin ≤95 g/L within 7 days of pediatric intensive care unit admission were randomized to receive prestorage leukocyte-reduced red-cell transfusion if their hemoglobin dropped either < 70 g/L (restrictive) or 95 g/L (liberal).
Measurements and main results: Postoperative cardiac patients (n = 125) from seven centers were enrolled. The restrictive (n = 63) and liberal (n = 62) groups were similar at baseline in age (mean ± standard deviation = 31.4 ± 38.1 mos vs. 26.4 ± 39.1 mos), surgical procedure, severity of illness (Pediatric Risk of Mortality score = 3.4 ± 3.2 vs. 3.2 ± 3.2), multiple organ dysfunction syndrome (46% vs. 44%), mechanical ventilation (62% vs. 60%), and hemoglobin (83 vs. 80 g/L). Mean hemoglobin remained 21 g/L lower in the restrictive group after randomization. No significant difference was found in new or progressive multiple organ dysfunction syndrome (primary outcome) in the restrictive group vs. liberal group (12.7% vs. 6.5%; p=.36), pediatric intensive care unit length of stay (7.0 ± 5.0 days vs. 7.4 ± 6.4 days) or 28-day mortality (3.2% vs. 3.2%).
Conclusion: In this subgroup analysis of cardiac surgery patients, a restrictive red-cell transfusion strategy, as compared with a liberal one, was not associated with any significant difference in new or progressive multiple organ dysfunction syndrome, but this evidence is not definitive.

Introduction

The impact of blood transfusions after cardiac surgery on outcome has been studied extensively in adults but not in children.^[1-5] A recent review evaluating the effect of blood transfusion on outcome of adult cardiac surgery patients reported that red-cell transfusion is associated with increased perioperative and long-term mortality and complications. In adults with cardiovascular disease, a restrictive transfusion strategy seemed safer.^[6] Adult and pediatric cardiac diseases differ fundamentally; in children, most cardiac surgeries address congenital malformations, whereas ischemic heart disease is rare.

Red-cell transfusions are administered during the postoperative period to most children who undergo cardiac surgery, even though the hemoglobin level at which the benefits of red-cell transfusion outweigh its associated risks is unknown.^[7-10] Significant variation in transfusion practice exists and it has been reported that the hemoglobin threshold at which practitioners transfuse is higher for children with cardiac disease.^{[8, 11, 12]} The TRIPICU (Transfusion Requirements in Pediatric Intensive Care Units) study, a randomized clinical trial (RCT) comparing outcome in a general population of stable critically ill children, showed that a restrictive transfusion strategy was not inferior to a liberal one with respect to new or progressive multiple organ dysfunction syndrome (MODS).^[13] We analyzed the subgroup of TRIPICU subjects who underwent cardiac surgery

Materials and Methods

A detailed description of the TRIPICU results was reported previously.^[13] The TRIPICU study enrolled stabilized critically ill children from 19 tertiary care pediatric intensive care units (ICUs). Children aged between 3 days and 14 yrs, with at least one hemoglobin concentration of ≤95 g/L within the first 7 days after pediatric ICU admission, were considered for inclusion. Exclusion criteria are listed in Figure 1. Participants were allocated randomly to restrictive (transfusion threshold = 70 g/L) or liberal (transfusion threshold = 95 g/L) treatment arms. Only prestorage leukocyte-reduced allogeneic red-cell units were used. Transfusion strategies were applied for up to 28 days post randomization; the research protocol allowed temporary suspension during active blood loss, surgery, severe hypoxemia, or hemodynamic instability

The primary outcome was the proportion of patients who developed or had progression of MODS, as defined by Proulx et al.^[14] We also looked at markers of severity of MODS (the highest number of organ dysfunction per patient and the Pediatric Logistic Organ Dysfunction [PELOD] score), and we collected information on secondary outcomes.^{[15, 16]}

Patients

This subgroup analysis focused on patients included in the TRIPICU study who had undergone cardiac surgery or catheterization. TRIPICU study exclusion criteria specific to this subgroup were: age < 28 days and patients with cyanotic heart disease (with right to left shunt) who had a palliative intervention (procedures such as Norwood, Glenn, Fontan, or a shunt between a systemic and a pulmonary artery were considered palliative). The baseline diagnosis and/or the procedure performed were recorded. Patients were categorized according to the Risk Adjusted Classification for Congenital Heart Disease Score (RACHS-1 score), with higher scores indicating a greater risk of death.^[17] This study was exempt from Institutional Review Board approval.

Statistical Analysis

Continuous variables were compared, using Student's t test or Wilcoxon rank sum test; categorical variables were analyzed using chi-square testing. Baseline characteristics were compared, using univariate descriptive statistics followed by logistic regression, to evaluate the effect on outcomes of clinically important covariates including patient age, country, and Pediatric Risk of Mortality scores.^[18]

It was estimated that at least 626 patients would be required to complete the TRIPICU study and test a noninferiority hypothesis (p< .05; power of 0.9; margin of safety: absolute risk reduction of 10%). This subgroup analysis involves 125 patients; the statistical analyses tested both superiority and noninferiority (same p value and margin of safety). Statistical analysis of the primary outcome measure was conducted, using an "intent-to-treat" approach. In the primary analysis, we calculated 95% Confidence Intervals (CI) around the absolute risk reduction in the proportion of patients with new or progressive MODS. We also conducted a per-protocol analysis of the primary outcome in patients who met or exceeded an 80% rate of protocol adherence. Adherence was defined as the proportion of days after randomization during which at least one hemoglobin concentration was above the transfusion threshold.

All secondary analyses were conducted, using an "intent-to-treat" approach. We compared daily PELOD scores, using the worst scores after baseline, and the total number of organ dysfunctions per patient. We also compared 28-day and hospital all-causes mortality, nosocomial infections, transfusion reactions, other adverse events, duration of mechanical ventilation, and pediatric ICU and hospital length of stay. To determine whether a restrictive transfusion strategy decreased exposure to red cells, we compared the total number of transfusions per patient and the proportion of patients who received no red-cell transfusion in the two groups.

Differences were considered statistically significant when a two-sided α level was < 0.05. No adjustments were made for multiple comparisons. Data were analyzed by a biostatistician (T.D.) with SAS software (version 9.1, SAS Institute, Cary, NC) and expressed as mean ± sd.

Results

Patients and Treatment Assignment

There were 125 patients in the cardiac surgery subgroup, representing 19.6% of all the TRIPICU patients, with 63 in the restrictive group and 62 in the liberal group . The two groups seemed similar at baseline. The most common surgeries were: coarctation repair (13 patients) in RACHS-1 category 1; ventricular septum defect repair^[16] and repair of tetralogy of Fallot^[24] in category 2; repair of atrioventricular canal^[11] and mitral valve surgery^[8] in category 3; Rastelli procedure^[8] and arterial switch^[5] in category 4. One patient in the liberal group underwent invasive cardiac catheterization. Although there were more patients in risk category 3 in the restrictive group (27 vs. 15), the difference was not statistically significant (p=.06). Pediatric Risk of Mortality score as well as the frequency and severity of MODS were similar at baseline

Intervention

The hemoglobin concentration at randomization in the restrictive and liberal groups was 83 ± 9 g/L and 80 ± 9 g/L, respectively. Time between randomization and first transfusion (1.8 ± 1.8 days vs. 0.06 ± 0.3 days; p< .01) as well as hemoglobin levels before the first transfusion (71 ± 6.0 g/L vs. 82 ± 1.0 g/L; p< .01) differed significantly. After randomization, an average difference in hemoglobin concentration of 21 g/L was observed (91 ± 13 g/L in the restrictive group and 112 ± 14 g/L in the liberal group.
Seven patients in the restrictive group and one in the liberal group were suspended temporarily from the transfusion protocol. Length of suspension was comparable (1.1 ± 0.4 days in the restrictive and 1.0 day in the liberal group). During the suspension period, seven red-cell transfusions were given in the restrictive group and one in the liberal group. Including the suspension period, a total of 13 transfusions were administered in the restrictive group and 82 in the liberal group (p< .01). In the restrictive group, 52 patients (83%) received no red-cell transfusion, whereas all patients in the liberal group were transfused (p< .01).

Cointerventions including vasoactive drugs (proportion of patients receiving at least one drug), fluid balance and administration of fresh-frozen plasma, platelets and albumin were similar. There was a trend toward higher corticosteroid use in the liberal group (14% vs. 27%; p=.07).

Primary Outcome

Eight patients in the restrictive and four patients in the liberal group (12.7% and 6.5%) developed or experienced worsened MODS after randomization; the absolute risk reduction in the liberal group was 6.2% (95% CI = -7.6% to +10.4%; p=.36); the upper limit of this 95% CI (+10.4%) overrides 10%, which means that noninferiority is not statistically supported.

We performed a per-protocol analysis of the primary outcome. As planned in the research protocol, we excluded from this analysis ten patients who did not meet our predefined criteria of good adherence, one wrongly included patient who was younger than 28 days and four patients who could not be categorized according to RACHS-1.^[19] A total of 115 patients met the 80% adherence criterion. The results of the per-protocol analysis (absolute risk reduction in the liberal group: 5.56%; 95% CI = -5.08 to +16.19; p=.37) differed only slightly from those of the intention-to-treat analysis (6.2%; 95% CI = -7.6% to +10.4%, p=.36).

Secondary Analyses

No difference was found for any other MODS descriptor (number of organ dysfunctions, PELOD score. No significant difference was observed in the number of nosocomial infections, oxygenation markers, duration of mechanical ventilation, length of ICU stay, or number of red-cell tranfusion reactions; 28-day mortality after randomization was equal (2 vs. 2).

Discussion

No RCT has been published on the efficacy of red-cell transfusion after pediatric cardiac surgery. This subgroup analysis of cardiac surgery patients enrolled in the TRIPICU study was planned before the trial was initiated. We found that a restrictive red-cell transfusion strategy, as compared with a liberal one, was not associated with any significant difference in new or progressive MODS, but the power of this subgroup analysis was not optimal. There seemed to be a trend toward more organ dysfunction in patients older than 365 days in the restrictive group, but the number of patients (4 of 30 vs. 0 of 25) was too small to permit any conclusions and such a trend was not found in younger patients (4 of 33 vs. 4 of 36). Furthermore, this trend was not found when quantitative markers of severity of MODS, like the highest number of organ dysfunctions (1.4 ± 1.2 vs. 1.34 ± 1.2) and the PELOD score (6.6 ± 9.4 vs. 5.8 ± 6.4), were compared.

This subgroup analysis is presently the only available description on transfusion threshold in pediatric cardiac surgery patients. The sample size required to complete a superiority RCT with a two-sided p value of .05 and a power of 0.90 would be 1010 patients (n = 2 × 505); 770 patients must be collected (n = 2 × 385) if the power is decreased to 0.80. The sample size required to complete a noninferiority RCT with the same assumptions as in the original TRIPICU study (one-sided p value of .05, power 0.90 and margin of safety of 10%) would be 638 patients (n = 2 × 319); 490 patients would be required (n = 2 × 245) if the power is decreased to 0.80.

We found that there were no clinically important nor statistically significant differences with regard to any secondary outcomes analyzed, including mortality, duration of mechanical ventilation, or length of stay, and that trends were similar for both analytic strategies applied (intent-to-treat and per-protocol analysis). There were too few patients to make strong inferences with respect to the safety of the transfusion strategies; furthermore, subgroup analysis can be used only to generate hypotheses, not to derive final conclusions.^[20] However, we did find a statistically and clinically significant difference with regard to red-cell transfusion: The restrictive strategy resulted in a six-fold reduction in both the number of patients who received a transfusion as well as the total number of red-cell transfusions.

Most of the literature on transfusion after cardiac surgery comes from adult studies, which showed that a lower transfusion threshold does not adversely affect patient outcome.^[5] A review by Murphy and Angelini found that most adult studies evaluating the effect of hemoglobin concentration on outcome after cardiac surgery were retrospective^[6] and that red-cell transfusions were associated with increased perioperative and long-term morbidity. A meta-analysis by Hill et al showed that restrictive transfusion triggers do not adversely affect mortality, cardiac morbidity, or hospital length of stay in patients who do not have advanced coronary artery disease.^[21] Findings from adults are not directly applicable to the pediatric population because cardiovascular physiology and pathology differ substantially.

In stabilized, critically ill children having undergone cardiac surgery, it is presently unclear what degree of anemia warrants red-cell transfusion. Although a higher hemoglobin level enhances global oxygen delivery, red-cell transfusions also carry the potential for harm. Adverse effects of transfusions include systemic inflammatory stimulation and blood flow disturbance in small vessels which may contribute to MODS, immune suppression, and transfusion-related reactions, such as transfusion-associated cardiac overload, transfusion-related acute lung injury, hemolytic reactions, and allergic reactions.^{[10, 22-24]}

In the absence of clear evidence, variation in clinical practice can be expected. In two scenario-based surveys, the hemoglobin concentration that would prompt pediatric intensivists to prescribe a red-cell transfusion during postoperative care of corrective cardiac surgery ranged from 70 g/L to 130 g/L.^{[11, 12]} There is also variability in the proportion of pediatric cardiac surgery patients reported to have received a red-cell transfusion during their postoperative care, with figures in the literature ranging from 24.6% to 93%.^{[8, 9]} Practitioners use higher transfusion thresholds for pediatric cardiac surgery patients than for other critically ill children.^[8] Both hemoglobin level thresholds used in the TRIPICU study (70 g/L and 95 g/L) are significantly lower than thresholds frequently used in the postoperative care of pediatric cardiac surgery, which are frequently >100 g/L.^[25] In our subgroup analysis, a restrictive strategy reduced substantially the number of red-cell transfusions and donor exposure.

This study has some limitations. It is possible that a site-related bias exists because only those centers whose cardiac surgeons and intensivists were willing to accept a lower hemoglobin included their cardiac patients in the study. A selection bias is also possible because some children may have received transfusions during or immediately after surgery that would have raised their hemoglobin level >95 g/L, thus excluding them from this trial. The TRIPICU study excluded neonates with congenital heart disease and cyanotic patients; consequently, our subgroup analysis does not apply to these patients. Minor imbalances were observed in the two groups with regard to the RACHS-1 risk classification; a per-protocol analysis taking this into account found no significant difference. In the restrictive group, the baseline hemoglobin level at randomization was 83 g/L. Thereafter, the average lowest hemoglobin level per day was 91 g/L; this increase was a surprise given that only 17% of the patients were transfused, but may be explained by the aggressive diuretic and fluid restriction therapy that is used in the postoperative care of pediatric cardiac surgery. In spite of this increase, the difference between the lowest hemoglobin level per day in the pediatric ICU was 21 g/L (91 g/L in the restrictive group vs. 112 g/L in the liberal group), which is the same difference observed in the full TRIPICU study.^{[13, 26]} The most important limitations of our study are a lack of power and the fact that a subgroup analysis should only be used to generate hypotheses.^{[20, 27]}

This study has several strengths. It is presently the only RCT studying transfusion threshold in pediatric cardiac surgery patients. This subgroup analysis was planned a priori. To avoid selection bias, only centers agreeing to consider the inclusion of all their cardiac surgery patients enrolled this type of patient into the TRIPICU study. It can be argued that the necessity to be stabilized selected less severely ill cardiac patients; nonetheless, those included were critically ill, with 62% requiring mechanical ventilation and 78% receiving inotropic and/or vasoactive support at randomization. Adherence to the research protocol was excellent and no patients were lost to follow-up. There was no difference in any cointervention. Even though the sample size is too small to perform definitive statistical analyses, it should be emphasized that the number of organ dysfunctions, the PELOD score, and all secondary outcomes were similar in both groups.

Conclusions

The British Society of Hematology supports the acceptance of a postoperative hemoglobin level of 70 g/L in both children and adults when there is good postoperative cardiac function.^[28] The Society of Thoracic Surgeons makes a similar recommendation for all cardiac surgery patients.^[29] In this analysis of the cardiac surgery subgroup from the TRIPICU study, we found that a restrictive red-cell transfusion strategy, as compared with a liberal one, was not associated with any significant difference in new or progressive MODS, but this evidence is not definitive. A larger study is necessary to determine if a lower transfusion threshold is safe in pediatric postoperative cardiac surgery patients; transfusion thresholds for children with uncorrected cyanotic heart lesions will require specific consideration.

References

• 1. Hebert PC, Yetisir E, Martin C, et al: Is a low transfusion threshold safe in critically ill patients with cardiovascular diseases? Crit Care Med 2001; 29:227-234
• 2. Fransen E, Maessen J, Dentener M, et al: Impact of blood transfusions on inflammatory mediator release in patients undergoing cardiac surgery. Chest 1999; 116:1233-1239
• 3. Engoren MC, Habib RH, Zacharias A, et al: Effect of blood transfusion on long-term survival after cardiac operation. Ann Thorac Surg 2002; 74:1180-1186
• 4. Kuduvalli M, Oo AY, Newall N, et al: Effect of peri-operative red blood cell transfusion on 30-day and 1-year mortality following coronary artery bypass surgery. Eur J Cardiothorac Surg 2005; 27:592-598
• 5. Bracey AW, Radovancevic R, Riggs SA, et al: Lowering the hemoglobin threshold for transfusion in coronary artery bypass procedures: Effect on patient outcome. Transfusion 1999; 39:1070-1077
• 6. Murphy GJ, Angelini GD: Indications for blood transfusion in cardiac surgery. Ann Thorac Surg 2006; 82:2323-2334
• 7. Bateman ST, Lacroix J, Boven K, et al: Anemia, blood loss, and blood transfusions in North American children in the intensive care unit. Am J Respir Crit Care Med 2008; 178:26-33
• 8. Armano R, Gauvin F, Ducruet T, et al: Determinants of red blood cell transfusions in a pediatric critical care unit: A prospective, descriptive epidemiological study. Crit Care Med 2005; 33:2637-2644
• 9. Petaja J, Lundstrom U, Leijala M, et al: Bleeding and use of blood products after heart operations in infants. J Thorac Cardiovasc Surg 1995; 109:524-529
• 10. Gauvin F, Lacroix J, Robillard P, et al: Acute transfusion reactions in the pediatric intensive care unit. Transfusion 2006; 46:1899-1908
• 11. Laverdiere C, Gauvin F, Hebert PC, et al: Survey on transfusion practices of pediatric intensivists. Pediatr Crit Care Med 2002; 3:335-340
• 12. Nahum E, Ben-Ari J, Schonfeld T: Blood transfusion policy among European pediatric intensive care physicians. J Intensive Care Med 2004; 19:38-43
• 13. Lacroix J, Hebert PC, Hutchison JS, et al: Transfusion strategies for patients in pediatric intensive care units. N Engl J Med 2007; 356:1609-1619
• 14. Proulx F, Fayon M, Farrell CA, et al: Epidemiology of sepsis and multiple organ dysfunction syndrome in children. Chest 1996; 109:1033-1037
• 15. Leteurtre S, Martinot A, Duhamel A, et al: Validation of the paediatric logistic organ dysfunction (PELOD) score: Prospective, observational, multicentre study. Lancet 2003; 362:192-197
• 16. CDC definitions for nosocomial infections, 1988. Am Rev Respir Dis 1989; 139:1058-1059
• 17. Jenkins KJ, Gauvreau K, Newburger JW, et al: Consensus-based method for risk adjustment for surgery for congenital heart disease. J Thorac Cardiovasc Surg 2002; 123:110-118
• 18. Pollack MM, Ruttimann UE, Getson PR: Pediatric risk of mortality (PRISM) score. Crit Care Med 1988; 16:1110-1116
• 19. Garrett AD: Therapeutic equivalence: Fallacies and falsification. Stat Med 2003; 22:741-762
• 20. Wang R, Lagakos SW, Ware JH, et al: Statistics in medicine-reporting of subgroup analyses in clinical trials. N Engl J Med 2007; 357:2189-2194
• 21. Hill SR, Carless PA, Henry DA, et al: Transfusion thresholds and other strategies for guiding allogeneic red blood cell transfusion. Cochrane Database Syst Rev 2002(2):CD002042
• 22. Vamvakas EC: Deleterious clinical effects of transfusion immunomodulation: Proven beyond a reasonable doubt. Transfusion 2006; 46:492-494; author reply, 494-495
• 23. Hebert PC, Wells G, Blajchman MA, et al: A multicenter, randomized, controlled clinical trial of transfusion requirements in critical care. Transfusion Requirements in Critical Care Investigators, Canadian Critical Care Trials Group. N Engl J Med 1999; 340:409-417
• 24. Doctor A, Platt R, Sheram ML, et al: Hemoglobin conformation couples erythrocyte S-nitrosothiol content to O² gradients. Proc Natl Acad Sci U S A 2005; 102:5709-5714
• 25. Desmet L, Lacroix J: Transfusion in pediatrics. Crit Care Clin 2004; 20:299-311
• 26. Hebert PC: Transfusion requirements in critical care (TRICC): A multicentre, randomized, controlled clinical study. Transfusion Requirements in Critical Care Investigators and the Canadian Critical care Trials Group. Br J Anaesth 1998; 81(Suppl 1):25-33
• 27. Oxman AD, Guyatt GH: A consumer's guide to subgroup analyses. Ann Intern Med 1992; 116:78-84
• 28. Gibson BE, Todd A, Roberts I, et al: Transfusion guidelines for neonates and older children. Br J Haematol 2004; 124:433-453
• 29. Ferraris VA, Ferraris SP, Saha SP, et al: Perioperative blood transfusion and blood conservation in cardiac surgery: The Society of Thoracic Surgeons and The Society of Cardiovascular Anesthesiologists clinical practice guideline. Ann Thorac Surg 2007; 83(5 Suppl):S27-S86

Biomarkers in Heart Failure

                                                                                    Eugene Braunwald, M.D

                                                           NEJM 2008;358:2148-59 - Review

Heart failure, a major and growing public health problem, appears to result not only from cardiac overload or injury but also from a complex interplay among genetic, neurohormonal, inflammatory, and biochemical changes acting on cardiac myocytes, the cardiac interstitium, or both. An increasing number of enzymes, hormones, biologic substances, and other markers of cardiac stress and malfunction, as well as myocyte injury - collectively referred to as biomarkers - appear to have growing clinical importance. Although biomarkers include genetic variants, clinical images, physiological tests, and tissue-specimen biopsies, this review focuses on biomarkers derived from the blood or urine other than serum levels of hemoglobin, electrolytes, liver enzymes, and creatinine, which are routinely determined as part of clinical care.

Morrow and de Lemos¹ have set out three criteria a biomarker should fulfill to be useful clinically. First, accurate, repeated measurements must be available to the clinician at a reasonable cost and with short turnaround times; second, the biomarker must provide information that is not already available from a careful clinical assessment; and finally, knowing the measured level should aid in medical decision making.

Although relatively few of the biomarkers discussed in this review satisfy all three criteria, many appear to provide important information regarding the pathogenesis of heart failure or the identification of subjects at risk for heart failure or appear to be useful in risk stratification, in the diagnosis of heart failure, or in monitoring therapy. Many biomarkers may be risk factors themselves and therefore may be potential targets of therapy. Although no specific classes for biomarkers are accepted, I propose that they could be divided into six categories, as well as a seventh category of new biomarkers that have not yet been fully characterized 

Inflammation

Inflammation is important in the pathogenesis and progression of many forms of heart failure, and biomarkers of inflammation have become the subject of intense inquiry³ Interest in the presence of inflammatory mediators in patients with heart failure began in 1954, when a crude assay for C-reactive protein, a protein that appears in the serum in a variety of inflammatory conditions, became available. A study published in 1956 reported that C-reactive protein was detectable in 30 of 40 patients with chronic heart failure and that heart failure was more severe in those with higher levels of C-reactive protein.⁴ Subsequently, C-reactive protein was described as an acute-phase reactant synthesized by hepatocytes in response to the proinflammatory cytokine interleukin-6.⁵ The use of C-reactive protein as a biomarker became more common when a low-cost, high-sensitivity test for C-reactive protein was developed.⁶ Multivariate analysis indicated that increased C-reactive protein level is an independent predictor of adverse outcomes in patients with acute or chronic heart failure.⁷ In the Framingham Heart Study, for example, C-reactive protein (as well as the inflammatory cytokines interleukin-6 and tumor necrosis factor [TNF- ]) was noted to identify asymptomatic older subjects in the community who were at high risk of the future development of Further, C-reactive protein has been shown to exert direct adverse effects on the vascular endothelium by reducing nitric-oxide release and increasing endothelin-1 production, as well as by inducing expression of endothelial adhesion molecules.⁹ These findings suggest that C-reactive protein may also play a causal role in vascular disease and could therefore be a target of therapy. However, elevated levels of C-reactive protein lack specificity; for example, acute and chronic infection, cigarette smoking, acute coronary syndromes, and active inflammatory states are frequently associated with elevated levels of C-reactive protein.

In 1990, Levine et al. described elevated levels of circulating TNF- in patients with heart failure.¹⁰ TNF- and at least three interleukins (interleukins 1, 6, and 18) are considered to be proinflammatory cytokines and are produced by nucleated cells in the heart.³ The cytokine hypothesis of heart failure proposes that a precipitating event - such as ischemic cardiac injury - triggers innate stress responses, including elaboration of proinflammatory cytokines, and that the expression of these cytokines is associated with deleterious effects on left ventricular function and accelerates the progression of heart failure¹¹. Proinflammatory cytokines appear to cause myocyte apoptosis and necrosis; interleukin-6 induces a hypertrophic response in myocytes,¹¹ whereas TNF- causes left ventricular dilatation, apparently through activation of matrix metalloproteinases. Interleukin-6 and TNF- levels could be used to predict the future development of heart failure in asymptomatic elderly subjects in one study,¹² though blockade of TNF- has not resulted in clinical benefit in patients with heart failure.^3,13 heart failure

Fas (also termed APO-1) is a member of the TNF- receptor family that is expressed on a variety of cells, including myocytes. When Fas is activated by the Fas ligand it mediates apoptosis and plays an important role in the development and progression of heart failure. Elevated serum levels of a soluble form of Fas have been reported in patients with heart failure, and high levels are associated with severe disease.¹⁴ The inhibition of soluble Fas in animals reduces postinfarction ventricular remodeling and improves survival.¹⁵ Pharmacologic efforts to reduce Fas levels are still in their infancy but may represent a new direction in the treatment or prevention of heart failure. Indeed, the administration of a nonspecific immunomodulating agent - pentoxifylline¹⁶ or intravenous immunoglobulin¹⁷ - reduces plasma levels of Fas as well as C-reactive protein and is reported to improve left ventricular function in patients with ischemic or dilated cardiomyopathy.

Thus, measurements of C-reactive protein, inflammatory cytokines, Fas, and their soluble receptors appear to be useful in risk stratification of patients with heart failure and in screening to identify asymptomatic subjects at risk for heart failure. In the future, the profile of changes in inflammatory biomarkers might help to identify the specific inflammatory disturbances in any given patient and thereby might aid the selection of appropriate therapy.

Oxidative Stress

Increased oxidative stress results from an imbalance between reactive oxygen species (including the superoxide anion, hydrogen peroxide, and the hydroxyl radical) and endogenous antioxidant defense mechanisms. The imbalance can exert profoundly deleterious effects on endothelial function¹⁸ as well as on the pathogenesis and progression of heart failure.¹⁹ Oxidative stress may damage cellular proteins and cause myocyte apoptosis and necrosis. It is associated with arrhythmias and endothelial dysfunction, with the dysfunction occurring through reduction of nitric oxide synthase activity as well as the inactivation of nitric oxide.²⁰ Inflammation and immune activation, activation of the renin-angiotensin-aldosterone system and the sympathetic nervous system, and increases in circulating catecholamine levels and peroxynitrite formed from the interaction of the superoxide anion and nitric oxide all may increase oxidative stress.²¹

Since it is difficult to measure reactive oxygen species directly in humans, indirect markers of oxidative stress have been sought. These include plasma-oxidized low-density lipoproteins, malondialdehyde and myeloperoxidase (an index of leukocyte activation), urinary levels of biopyrrins (oxidative metabolites of bilirubin),²² and isoprostane levels in plasma and urine.²³ The levels of plasma myeloperoxidase²⁴ and isoprostane excretion correlate with the severity of heart failure and are independent predictors of death from heart failure, even after adjustment for baseline variables.²⁶ The urinary excretion of 8-isoprostane correlates with the plasma levels of matrix metalloproteinases, which at high levels can accelerate adverse ventricular remodeling and increase the severity of heart failure.²⁶

There is increasing evidence that xanthine oxidase, which catalyzes the production of two oxidants, hypoxanthine and xanthine, plays a pathologic role in heart failure.²⁷ Uric acid production is elevated in association with increased xanthine oxidase activity. Elevated levels of uric acid correlate with impaired hemodynamics²⁸ and independently predict an adverse prognosis in heart failure.²⁹ Although more studies are required, uric acid may prove to be a simple, useful, albeit nonspecific, clinical indicator of excess oxidative stress.

Extracellular-Matrix Remodeling

Remodeling of the ventricles plays an important role in the progression of heart failure.³⁰ The extracellular matrix provides a "skeleton" for myocytes and determines their size and shape. Normally, there is a balance between matrix metalloproteinases (proteolytic enzymes that degrade fibrillar collagen) and tissue inhibitors of metalloproteinases. An imbalance, with dominance of matrix metalloproteinases over tissue inhibitors of metalloproteinases, is associated with ventricular dilatation and remodeling. An abnormal increase in collagen synthesis may also be deleterious to cardiac function because the resultant excessive fibrosis can impair ventricular function. The propeptide procollagen type I is a serum biomarker of collagen biosynthesis. Querejeta et al.³¹ observed a positive correlation between the serum level of propeptide procollagen type I and the fractional volume of fibrous tissue determined from cardiac biopsies in patients with essential hypertension. Cicoira et al.³² reported that the level of plasma procollagen type III in patients with heart failure is an independent predictor of adverse outcomes.

Thus, elevated markers of increased extracellular-matrix breakdown on the one hand and of excessive collagen synthesis on the other are associated with impaired left ventricular function and adverse clinical outcomes in patients with heart failure. Markers of these processes appear to be important targets of therapy. However, at least 15 matrix metalloproteinases and several forms of procollagen and of tissue inhibitors of metalloproteinases have been identified.  Which of these are the most informative and appropriate for routine measurement requires clarification.³³

Neurohormones

In the early 1960s it was reported that patients with heart failure had abnormally elevated levels of plasma norepinephrine at rest and that further elevations occurred during exercise.³⁴ The urinary excretion of norepinephrine was also increased.³⁵ These findings suggested that the sympathetic nervous system is activated in patients with heart failure and that a neurohormonal disturbance might play a pathogenetic role in heart failure. Cohn et al.³⁶ subsequently demonstrated that plasma norepinephrine level was an independent predictor of mortality. Swedberg et al.³⁷ made the important observation that the renin-angiotensin-aldosterone system becomes activated in patients with heart failure as well.

Subsequently, after its discovery, attention focused on big endothelin-1, a 39-amino-acid prohormone secreted by vascular endothelial cells that is converted in the circulation into the active neurohormone endothelin-1, a peptide hormone 21 amino acids in length. Endothelin-1 is a powerful stimulant of vascular smooth-muscle contraction and proliferation and ventricular and vessel fibrosis and is a potentiator of other neurohormones.³⁸ The plasma levels of both endothelin-1 and big endothelin-1 are increased in patients with heart failure and correlate directly with pulmonary artery pressure,³⁹ disease severity, and mortality.⁴⁰ The Valsartan Heart Failure Trial (Val-HeFT) investigators compared the prognostic values of plasma neurohormones (norepinephrine, plasma renin activity, aldosterone, endothelin-1, big endothelin-1, and brain natriuretic peptide [BNP]) among 4300 patients.⁴¹ The most powerful predictors of mortality and hospitalization for heart failure, after BNP, were big endothelin-1, followed by norepinephrine, endothelin-1, plasma renin activity, and aldosterone. However, trials involving several endothelin-1-receptor antagonists have failed to show any beneficial effects on clinical outcomes.³⁸

In the Randomized Aldactone Evaluation Study (RALES) of patients with severe heart failure, Zannad et al.⁴² found that administration of the aldosterone blocker spironolactone was associated with a reduction of plasma procollagen type III and clinical benefit, but only in patients whose baseline levels of the procollagen were above the median. Administration of spironolactone in patients with acute myocardial infarction reduced myocardial collagen synthesis, as reflected by plasma procollagen type III, as well as postinfarct adverse left ventricular remodeling.⁴³ Taken together, these findings suggest that limiting the synthesis of the extracellular matrix might be an important component of the beneficial action of spironolactone in patients with severe heart failure.

Arginine vasopressin is a nonapeptide that is synthesized in the hypothalamus and stored in the posterior pituitary gland and that has antidiuretic and vasoconstrictor properties. Excess release of arginine vasopressin intensifies heart failure associated with dilutional hyponatremia, fluid accumulation, and systemic vasoconstriction. Whereas plasma levels of arginine vasopressin are elevated in patients with acute or chronic heart failure⁴⁴ and are associated with poor clinical outcomes, blockade of the vasopressin 2 receptor relieves acute symptoms but does not appear to alter the natural history of severe heart failure.⁴⁵ Thus, it is not yet clear whether the vasopressin 2 receptor should be considered to be a therapeutic target.

Although elevated levels of several neurohormones can be used to predict adverse outcomes in patients with heart failure, they are relatively unstable in plasma and may be difficult to measure on a routine basis. However, it is likely that these neurohormones are important contributors to the pathophysiological changes that occur in heart failure. Although the various neurohormones are distinct, they have common features. Norepinephrine, angiotensin II, aldosterone, endothelin-1, and arginine vasopressin are vasoconstrictors, thereby increasing ventricular afterload. The fact that blockade of the sympathetic nervous system and of the renin-angiotensin-aldosterone system are cornerstones of current pharmacologic treatment of heart failure supports the concept that several of these biomarkers are probably part of the direct causal pathway for heart failure.

Myocyte Injury

Myocyte injury results from severe ischemia, but it is also a consequence of stresses on the myocardium such as inflammation, oxidative stress, and neurohormonal activation. During the past two decades, the myofibrillar proteins - the cardiac troponins T and I - have emerged as sensitive and specific markers of myocyte injury and have improved greatly the diagnosis, risk stratification, and care of patients with acute coronary syndromes.

Modest elevations of cardiac troponin levels are also found in patients with heart failure without ischemia.⁴⁶ Horwich et al.⁴⁷ reported that cardiac troponin I was detectable ( 0.04 ng per milliliter) in approximately half of 240 patients with advanced, chronic heart failure without ischemia. After adjustment for other variables associated with poor prognosis, the presence of cardiac troponin I remained an independent predictor of death. Cardiac troponin T levels greater than 0.02 ng per milliliter in patients with chronic heart failure were associated with a hazard ratio for death of more than 4⁴⁸ In this issue of the Journal, Peacock et al.⁵⁰ report that troponin measurements are a predictor of outcome in hospitalized patients with acute decompensated heart failure. Latini et al.⁵¹ found that, with a standard assay, cardiac troponin T was detectable in 10% of patients with chronic heart failure, but with a new high-sensitivity assay, it was detectable in 92% of these patients. After adjustment for baseline variables and BNP level, the detection of troponin T by means of the high-sensitivity assay was associated with an increased risk of death. This study showed that previously nondetectable levels of cardiac troponin T can provide important additional prognostic information. As the sensitivity of cardiac troponin analysis increases further, the biomarker will probably be detectable in the entire population, and along with the natriuretic peptides it will be used routinely to assess the prognosis and response to treatment of patients with heart failure. propriate for routine measurement requires clarification.³³

Other myocardial proteins - including myosin light chain 1, heart fatty-acid binding protein, and creatine kinase MB fraction - also circulate in stable patients with severe heart failure. Like cardiac troponin T, the presence of these myocardial proteins in the serum is an accurate predictor of death or hospitalization for heart failure.⁵² Future studies should compare the predictive accuracy of troponin measured with a high-sensitivity assay and the predictive accuracy of these other biomarkers of myocyte injury to determine whether the latter add information.

Myocyte Stress

Natriuretic Peptides

The precursor of BNP and N-terminal pro-brain natriuretic peptide (NT-pro-BNP) is a pre-prohormone BNP, a 134-amino-acid peptide that is synthesized in the myocytes and cleaved to the prohormone BNP of 108 amino acids. The prohormone is released during hemodynamic stress - that is, when the ventricles are dilated, hypertrophic, or subject to increased wall tension.⁵³ Prohormone BNP is cleaved by a circulating endoprotease, termed corin, into two polypeptides: the inactive NT-pro-BNP, 76 amino acids in length, and BNP, a bioactive peptide 32 amino acids in length. BNP causes arterial vasodilation, diuresis, and natriuresis, and reduces the activities of the renin-angiotensin-aldosterone system and the sympathetic nervous system. Thus, when considered together, the actions of BNP oppose the physiological abnormalities in heart failure.

The natriuretic peptides are cleared by the kidneys, and the hypervolemia and hypertension characteristic of renal failure enhance the secretion and elevate the levels of BNP, especially the NT-pro-BNP.⁵⁴ There is also a moderate increase in the level of circulating BNP with increasing age, presumably in relation to myocardial fibrosis or renal dysfunction, which are common in the elderly.⁵⁵ Pulmonary hypertension from a variety of causes may increase the plasma level of BNP.⁵² The level varies inversely with the body-mass index.⁵⁵ All of these physiological conditions and disease states must be taken into consideration in the interpretation of natriuretic peptides in individual patients. Assays for BNP and NT-pro-BNP are commercially available, and these biomarkers of heart failure are the most widely tested; such testing is recommended in current guidelines.^55,56

Measuring levels of BNP is most useful in the evaluation of patients with dyspnea presenting to the emergency department, where point-of-care testing may provide the advantages of convenience and rapid turnaround times, thereby facilitating clinical management. Maisel et al.⁵⁷ showed in the Breathing Not Properly study that BNP levels greatly increased the accuracy of the diagnosis of heart failure in patients presenting to emergency departments with dyspnea; in these patients, a level of more than 100 pg per milliliter renders the diagnosis of heart failure unlikely, whereas a level of more than 400 pg per milliliter makes the diagnosis likely. Similar findings, albeit with different cutoff values, were reported from the ProBNP Investigation of Dyspnea in the Emergency Department (PRIDE) study.⁵⁸ The cutoff values may differ in patients with chronic heart failure as compared with patients with acute heart failure. For example, in one series of patients with established chronic symptomatic heart failure, one fifth had plasma BNP levels below 100 pg per milliliter.⁵⁹

As compared with standard care, a strategy using a single measurement of BNP or NT-pro-BNP in patients presenting with acute dyspnea was associated with a shorter hospital stay and lower cost of hospitalization.^60,61 Thus, in patients presenting to the emergency department with possible heart failure, decisions regarding hospital admission or referral to an outpatient clinic are facilitated by knowledge of natriuretic peptide levels. BNP level is also an accurate predictor of survival in patients with acute decompensated heart failure, irrespective of left ventricular ejection fraction. Fonarow et al.⁶² measured the level at hospital admission in 48,629 patients with acute decompensated heart failure in the Acute Decompensated Heart Failure (ADHERE) registry (ClinicalTrials.gov number, NCT00366639 [ClinicalTrials.gov] ). After adjustment for baseline variables, an almost linear relation between BNP level and in-hospital mortality was found.

Measurements of BNP appear to be useful in the diagnosis and risk stratification of patients with chronic heart failure^52,54 and are a better predictor of death than is plasma norepinephrine²⁵ or endothelin-1.⁶³ In the Systolic Heart Failure Treatment Supported by BNP (STARS-BNP) trial, Jourdain et al.⁶⁴ randomly assigned outpatients with New York Heart Association class II or III heart failure to receive therapy either according to current clinical guidelines (control group) or with a goal of decreasing BNP levels to less than 100 pg per milliliter. The primary end point (death from heart failure or hospital admission for heart failure) occurred in 24% of patients in whom the BNP level was lowered, as compared with 52% of the control group (P<0.001), suggesting that therapy directed by BNP level is superior to guideline-directed therapy. Logeart et al.⁶⁵ reported that, in patients hospitalized for decompensated heart failure, the predischarge level of BNP was a strong, independent predictor of postdischarge outcomes and proposed that patients with heart failure whose BNP level does not decline to below approximately 600 pg per milliliter should receive intensified treatment before discharge.