Conversion between B-type natriuretic peptide and N-terminal pro B-type natriuretic peptide in perioperative risk assessment: protocol for a prospective cohort study

INTRODUCTION: Both B-type natriuretic peptide (BNP) and N-terminal pro-BNP (NT-pro-BNP) are used to identify patients at risk of perioperative vascular events, but prognostic thresholds have been established in a large prospective cohort for NT-pro-BNP only. We designed this study to inform perioperative risk interpretation of BNP values. Our primary objective is to validate a formula to convert BNP to NT-pro-BNP concentrations before non-cardiac surgery. The secondary objective is to determine the association between BNP categories (established based on conversion from NT-pro-BNP categories) and a composite outcome of myocardial injury after non-cardiac surgery (MINS) and vascular death. METHODS AND ANALYSIS: This is a single-centre, prospective cohort study in patients undergoing non-cardiac surgery who are >65 years old, Revised Cardiac Risk Index ≥1 or >45 years old with significant cardiovascular disease. BNP and NT-pro-BNP will be measured preoperatively, and troponin measurements will be analysed on postoperative days 1, 2 and 3. MINS and vascular death will be ascertained up to 30 days after surgery. The primary analyses will compare measured NT-pro-BNP values to those predicted by an existing formula (from a non-surgical population) based on BNP concentrations and patient characteristics, and recalibrate and update the formula with additional variables. Secondary analyses will estimate the relationship between categories of measured BNP (corresponding to established NT-pro-BNP thresholds) and the composite of MINS and vascular death. The target sample size of 431 patients is based on our primary analysis (assessing the conversion formula). ETHICS AND DISSEMINATION: Ethics approval has been obtained by the Queen's University Health Sciences Research Ethics Board, and all participants will provide informed consent for participation in the study. The results will be submitted for publication in conferences and in a peer-reviewed journal, and will inform perioperative vascular risk interpretation of preoperative BNP. TRIAL REGISTRATION NUMBER: NCT05352698.