B-type natriuretic peptide as a predictor of outcome in a general intensive care unit

摘要

Outcome prediction is a key issue in modern medicine. The possibility to estimate in advance and with reasonable precision the probability of a given disease to evolve in a certain direction once optimal care is delivered is crucial for both physicians and patients. The formers are expected to communicate healing possibilities, to promptly decide which intensity of care will optimize outcome and to correctly allocate resources also avoiding futile diagnostic or therapeutic procedures. For the latters and their families, the knowledge of future implications of patients’ condition is the backbone of the recovery process or of the approach to the end of life. In critical care medicine, outcome estimation is particularly important because of high costs and resource paucity. In this setting, severity scores have been developed as an aid in physiology derangement evaluation, risk stratification, study comparison and performance monitoring. Since the probability of dying in the hospital is an important parameter for clinical decision-making, the possibility to derive it from severity scores has been tested and confirmed: the Simplified Acute Physiology Score (SAPS) II, one of the most commonly used intensive care unit (ICU) classification systems, has been shown to be a reliable tool in predicting in-hospital death [1]. However, its computation is relatively time-consuming and implies to consider multiple variables and their worst values in the first 24 hours of ICU stay. Hence, it is unavailable in the very first hours after admission, when the most critical decisions have to be taken. Finding a simpler and more readily-obtainable indicator of severity to assist in ICU decision-making would be of paramount importance. Ideally, it should be available in a short-time period after admission, it should be obtained through routinely-implemented procedures and its calculation should not impose additional tasks on clinical staff. B-type natriuretic peptide (BNP) is a widely recognized independent predictor of outcome in cardiac disease like heart failure [2,3] acute coronary syndromes, [4,5] pulmonary embolism [6,7] and aortic stenosis [8]. In critical illness BNP is frequently elevated on a multifactorial basis and independently from primary cardiac pathologies [9,10]. Nonetheless, BNP measurement is advocated in this setting, mainly as an aid in the differential diagnosis of respiratory failure [11]. The hypothesis that BNP could be used as a predictor of unfavorable outcome in ICU patients has been previously explored [9,12,13,14,15,16,17]. However, the evidence about this subject remains controversial with some studies confirming the association between BNP or N Terminal -pro-BNP (NT-pro-BNP) levels and in-hospital mortality [9,13,15,16,17] and others denying it [12,13,14]. Furthermore, most of the existing studies used some form of entry selection, either at the level of ICU admission or of patient eligibility. Probably, increased BNP levels found in general medical/surgical ICU patients is an aspecific final common pathway shared, through different mechanisms, by many failing organs [9] and is also part of the neuroendocrine response to severe inflammation [18,19]. We hypothesized therefore that it could be seen as an objective and easy-to-obtain marker that reflects the severity of a patient’s global physiology derangement. The primary aim of the study was to investigate the relationship between BNP and hospital mortality. The secondary aim was to investigate the association between BNP and SAPS II.