Preoperative B-type natriuretic peptide risk stratification: do postoperative indices add value?

Abstract

Objectives: It is unclear if there is value in measuring postoperative B-type natriuretic peptide (BNP) in patients risk-stratified using preoperative BNP. Design: Prospective observational study. Setting and subjects: Patients undergoing vascular surgery at Inkosi Albert Luthuli Hospital, Durban. Data on intraoperative risk predictors, i.e. the nature of the surgery, number of transfused red blood cell units and the duration of surgery, were collected. Preoperative and postoperative BNP, electrocardiographic and troponin I monitoring were performed. Multivariable analysis was conducted to identify independent predictors of adverse cardiac events and then tested using reclassification statistics. Outcome measures: The composite of troponin elevation within the first three postoperative days and all-cause mortality within 30 days of surgery. Results: In 149 eligible patients, the study outcome occurred in 27 patients and was independently predicted by red blood cell (RBC) transfusion [odds ratio (OR) 1.8, 95% confidence interval (CI):1.08-3.08] and postoperative ischaemia (OR 7.1, 95% CI: 2.78-18.2). Postoperative BNP was not statistically significantly associated with the outcome (OR 2.1, 95% CI: 0.81-5.45, p-value = 0.13). In patients who were risk stratified using preoperative BNP, postoperative ischaemia appropriately improved risk classification overall (a net reclassification improvement of 82.5%, p-value < 0.001). Conclusion: RBC transfusion and postoperative ischaemia, but not postoperative BNP, were independent predictors of the composite outcome of all-cause mortality or postoperative troponin elevation. Postoperative ischaemia improved overall risk classification.