Validity of brain natriuretic pepide as a marker for adverse postoperative outcomes in patients undergoing cardiac surgery

We read with great interest the best evidence topic by Mitchell and Webb [1] evaluating current best available evidence to verify the validity of brain natriuretic pepide (BNP) as a marker for adverse postoperative outcomes in patients undergoing cardiac surgery. We feel that the clinical bottom line very nicely summarizes the current status of BNP as a predictor for adverse outcomes after cardiac surgery. Natriuretic peptides (NPs) have been found to be useful markers in differentiating acute dyspneic patients presenting to the emergency department and emerged as potent prognostic markers for patients with congestive heart failure (CHF). The best-established and widely used clinical application of BNP and NT-proBNP testing is for the emergent diagnosis of CHF in patients presenting with acute dyspnea. BNP and NT-proBNP, as the European Society of Cardiology recommended, are helpful in the diagnosis of HF and providing prognostic potential; as well at a low-normal concentration in untreated patients makes HF unlikely as the cause of symptoms [2]. The Food and Drug Administration (FDA) approved a cutoff value of BNP for the diagnosis of CHF as 100 pg/ml. In NT-proBNP, the optimal cutoff values for confirmatory decision limits for CHF are 450, 900 and 1800 pg/ml for ages <50 years, between 50 and 75 years, and older than 75 years of age. The exclusionary decision limit of NT-proBNP for cardiogenic acute dyspnea in all ages is <300 pg/ml [3]. BNP levels are influenced by age, gender and, to a surprisingly large extent, by body mass index. In addition, it can be elevated in a wide variety of clinical settings with or without CHF. BNP is elevated in other cardiac disease states such as the acute coronary syndromes, diastolic dysfunction, atrial fibrillation, amyloidosis, restrictive cardiomyopathy, and valvular heart disease. BNP is elevated in non-cardiac diseases such as pulmonary hypertension, chronic obstructive pulmonary disease, pulmonary embolism, and renal failure. BNP is also elevated in the setting of critical illness, such as in acute decompensated CHF and sepsis [4]. This variation across clinical settings has significant implications given the increasing frequency with which BNP testing is being performed. It is therefore important for clinicians to understand how to appropriately interpret BNP in light of the comorbidities of individual patients to maximize its clinical utility. Despite all the aforementioned potential indications for the role of BNP as a diagnostic and prognostic marker it must, however, be reiterated that currently the only reasonable practical application of BNP as a marker is limited to differentiation of acute dyspnea, monitoring of therapeutic responses, and prognosis of acute or decompensated CHF.