STUDIES OF CARDIOPULMONARY BYPASS IN CHILDREN - IMPLICATIONS FOR THE REGULATION OF BRAIN NATRIURETIC PEPTIDE

Objective: The aim was to examine the influence of cardiopulmonary bypass on brain natriuretic peptide (BNP) and on hormones of importance in the control of sodium and water balance and blood volume. Methods: Nine patients (mean age 4 years, range 2-9) undergoing cardiac surgery were studied. Blood samples were taken before, during, and up to 24 h after bypass. Plasma levels of BNP, atrial natriuretic peptide (ANP), arginine vasopressin (AVP), plasma renin activity, aldosterone. and catecholamines were measured. Results: Preoperative concentrations of plasma BNP [573(SEM 68) pg.ml-1] and ANP [332(74) pg.ml-1] were greatly increased (p<0.05) before bypass in all patients when compared to normal levels in children [BNP=31(4) pg.ml-1; ANP=27(3) pg.ml-1, n=28]. With general anaesthetic and sternotomy, there were large reductions (p<0.05) in both plasma BNP [180(62) pg.ml-1] and plasma ANP [163(59) pg-ml-1]. During bypass, there were no further significant decreases in plasma ANP or BNP concentrations compared with preoperative levels. Postoperatively, plasma BNP gradually increased for 12 h, to 170(28) pg.ml-1, whereas plasma ANP showed a further small decrease, to 107(20) pg.ml-1. However, postoperative plasma levels of both ANP and BNP remained well below preoperative values (p<0.01). Plasma AVP increased rapidly within 15 min of the onset of bypass, reaching a peak value of 153(5) pg.ml-1 after 45 min. Off bypass, plasma AVP decreased slowly and was still almost 10-fold above preoperative levels 12 h after end of bypass [137(11) pg.ml-1]. Mean central venous pressure decreased during the onset of bypass. from 4.3(1.9) to 0.4(1.1) mm Hg (p<0.05), and increased again at the end of bypass, to 9.0(3.3) mm Hg (p<0.05); there was little further change during the postoperative period. Conclusions: The major source of plasma BNP in patients with congenital heart disease is the cardiac ventricle. The lower plasma ANP and BNP levels and the narrow band of change in central venous pressure following surgical repair of cardiac abnormalities may be a response to improved cardiac function.