Brain natriuretic peptide and fluid volume homeostasis--studies during cardiopulmonary bypass surgery

Brain natriuretic peptide (BNP) is a recently identified cardiac ventricular hormone with diuretic, natriuretic and vasorelaxant properties. The aim of our study was to examine whether serial changes in endogenous levels of BNP were associated with fluid volume homeostasis following cardiopulmonary bypass. We studied nine patients undergoing elective cardiac surgery for the repair of cardiac abnormalities requiring cardiopulmonary bypass. Urinary levels of cyclic guanosine monophosphate (cGMP), sodium, urine output, fluid balance, and plasma levels of BNP, aldosterone, plasma renin activity (PRA) and central venous pressure (CVP) were measured before, during and after cardiopulmonary bypass. Basal pre-operative plasma BNP levels were highly elevated in all nine patients with cardiac abnormalities. During bypass, pre-operative levels of BNP, urinary cGMP and plasma aldosterone decreased significantly (p < 0.05), whereas pre-operative levels of urinary sodium and PRA were slightly reduced. During recovery following bypass levels of urinary cGMP, sodium, PRA and aldosterone returned to basal pre-operative values, whereas post-operative levels of plasma BNP were found to be three-fold below basal pre-operative levels. CVP (4.3 +/- 0.2 mmHg) during the onset of bypass increased significantly (p < 0.05) at the end of bypass (9 +/- 0.3 mmHg) followed by a modest increase post-operatively (10 +/- 0.4 mmHg). After operation only BNP had a significant correlation with urine output (r = -0.82, p < 0.02) and net fluid balance (r = -0.84, p < 0.01), whereas urinary cGMP, PRA and aldosterone all exhibited a non-significant correlation with urine output.(ABSTRACT TRUNCATED AT 250 WORDS)