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Assessment of preoperative B-type natriuretic peptide in adult surgeries: is it useful?

B-type natriuretic peptide (BNP) is secreted primarily by ventricular myocytes in response to increased wall stress induced by volume expansion, pressure overload, or ischemia of the cardiac chambers. Elevated plasma BNP is a proven diagnostic and prognostic biomarker in the setting of ambulatory heart failure and acute coronary syndromes. With BNP established as clinically relevant in nonsurgical cohorts, efforts have moved to determining whether preoperative BNP can be used to improve risk stratification of surgical patients. This interest is prompted by the fact that the majority of significant postoperative complications are cardiovascular. Worldwide, about 200 million noncardiac surgeries are performed annually, with conservative estimates indicating approximately 1 million accompanying adverse postoperative cardiac events. Surgical risk models that use patients’ clinical risk factors alone miss a sizeable proportion of patients who go on to develop adverse postoperative cardiovascular events. Furthermore, the American College of Cardiology/American Heart Association’s perioperative guidelines strongly emphasize patients’ functional status when determining who warrants preoperative cardiac testing, yet surgical patients are frequently elderly and have limited preoperative physical activity levels. A preoperative biomarker test, therefore, could prove very useful for surgical risk stratification and perioperative patient care if it is easy and inexpensive to measure, is sensitive and specific for cardiac pathology and adverse postoperative cardiovascular outcomes, adds to what can be anticipated using clinical criteria or routine cardiac testing, and can be used to direct perioperative management changes to improve patient outcomes. Several metaanalyses of studies of noncardiac surgical patients have shown that elevated preoperative BNP or N-terminal proBNP (NT-proBNP) is strongly associated with adverse short and longer term postoperative major adverse cardiovascular events and mortality. Furthermore, the meta-analysis by Lurati Buse et al. in this issue of Anesthesia & Analgesia illustrates that elevated preoperative BNP is associated with all-cause mortality in both noncardiac and cardiac surgical patients, with BNP thresholds providing high negative predictive value in both surgical groups. What remains to be delineated is precisely how physicians and patients should interpret and use preoperative BNP measurements for perioperative planning to prevent adverse postoperative patient outcomes. Although there are strong associations between elevated circulating BNP and the development of adverse outcomes after surgery, a major challenge facing the use of BNP for surgical risk stratification and patient care lies in identifying useful preoperative BNP thresholds or cut-points above which a patient is deemed “at risk.” There is substantial heterogeneity in the BNP thresholds described in the studies reporting significant associations between elevated preoperative BNP and adverse postoperative outcomes. Potential reasons for this heterogeneity include variability in commercially available BNP assays as well as between study differences in the types of surgical patients assessed (i.e., differences in overall cardiovascular health of studied surgical cohorts). NT-proBNP has a longer half-life than does BNP, so its levels are elevated when compared with a BNP measurement performed on the same blood sample. Additionally, there are multiple commercially available assays for measuring both BNP (active fragment) and NT-proBNP (inactive fragment), with some between-assays variability. Cut-points identified in the literature for clinical use should therefore be considered specific to the assessed BNP assay. Also contributing to variability in reported BNP risk thresholds is the fact that BNP (or NT-proBNP) is elevated in the setting of even subtle myocardial stress or failure and becomes progressively more elevated as myocardial stress increases. Therefore, the normal range of BNP varies according to surgical population (i.e., preoperative BNP levels will differ according to the cardiac disease burden of specific surgical populations). For example, this is why aortic valve replacement patients generally have higher preoperative BNP values than do patients undergoing isolated coronary artery bypass grafting, or why vascular surgical patients (who often have coronary artery disease) generally have higher preoperative BNP values than do From the Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women’s Hospital, Boston, Massachusetts.