Perioperative changes in plasma brain natriuretic peptide and N-terminal probrain natriuretic peptide in patients undergoing coronary bypass surgery under cardiopulmonary bypass

Introduction

Brain natriuretic peptide (BNP) is secreted by the cardiac ventricles in response to volume expansion and pressure overload. BNP and N-terminal (NT) proBNP are biochemical markers of left ventricular function [1]. In cardiac surgery at the present time there are few studies devoted to the evolution of natriuretic peptides into the perioperational period [2–5].

Objective

The aim of our study was to examine the release pattern of BNP and NT proBNP in the perioperative period of coronary surgery in two groups of patients: ventricular ejection fraction (VEF) > 50% and VEF < 50%. A secondary aim was to compare plasmatic levels of BNP and NT proBNP with the homodynamic parameters.

Methods

(1) Twenty-one patients undergoing coronary artery bypass grafting (CABG) by sternotomy, cardiopulmonary bypass (CPB) and moderate systemic hypothermia were divided into two groups: group I = 11 patients with normal left ventricular ejection fraction (LVEF > 50%) and group II = 10 patients with deteriorated LVEF (LVEF < 50%). Intraoperative anesthetic management was uniform for all patients. (2) Blood sampling was taken before surgical incision, after removal of the aortic cross clamp (10 min following cross-clamp removal) and after surgery: at the arrival in intensive care (T0) and 3, 6, 9, 12, 24, and 48 hours and 8 days after CPB. BNP and NT proBNP concentrations were measured by electrochemiluminescence immunoassay. (3) Hemodynamic parameters were measured at the same time with blood samples taken.

Statistics

Statistical comparisons were performed by the Mann–Whitney U test and the Wilcoxon nonparametric test. P < 0.05 was considered to indicate statistical significance.

Results

BNP and NT proBNP decreased when the aortic clamp was applied. After removal of the aortic cross clamp, BNP and NT proBNP increased gradually in the two groups. The peak of BNP ranges between 12 and 24 hours and the peak of NT proBNP ranges between 24 and 48 hours. BNP and NT proBNP increased in the same manner, in a similar exponential fashion, until 12 hours after surgery. The logarithmic model showed the same constant of time in both groups.

There is a good correlation between BNP and NT proBNP with the hemodynamic parameters of the left ventricle.

Discussion

In this cohort of uncomplicated CABG patients, BNP and NT proBNP increase in a similar exponential fashion until 12 hours after surgery. This very strong correlation between BNP and NT proBNP at all time points with baseline values implies that there is a similar process occurring in all our patients undergoing cardiac surgery. NT proBNP is more sensitive than BNP to the change of the hemodynamic parameters.

Conclusions

(1) This consistent and predictable pattern of BNP and NT proBNP release following CPB enables us to conceive a mathematical model of evolution of BNP and NT proBNP after uncomplicated cardiac surgery. The pattern may be different when there is postoperative ventricular dysfunction. (2) The strong correlation between the plasma NT proBNP concentration and the systemic vascular resistance means that the NT proBNP vasorelaxation action may be important for maintaining homeostasis after cardiac surgery.