GUT MUCOSAL PERFUSION IN NEONATES UNDERGOING CARDIOPULMONARY BYPASS

We studied gut mucosal perfusion in 24 neonates requiring cardiopulmon ary bypass (CPB). Group A patients (n = 12) had obstruction to their a orta such that gut perfusion before operation was dependent on flow th rough a ductus arteriosus (DA). Group B neonates were of similar age a nd size and required a similar duration of CPB, but did not have a DA. An orogastric tonometer allowed intermittent calculations of gastric intramucosal pH (pH(i)), and rectal mucosal perfusion (''flux'') was m onitored using laser Doppler flowmetry. Measurements of arterial base deficit, and lactate and pyruvate concentrations were made intermitten tly. Before CPB, mean femoral arterial pressure (MAP) and base deficit in group A were not significantly different from those in group B. Ho wever, mean flux before CPB was significantly lower and the lactate/py ruvate (L/P) ratio was significantly higher in group A compared with g roup B. Mean pH, was below normal (<7.26) throughout the operative per iod in group A, although it remained normal (>7.33) in group B. After corrective surgery, both during warm CPB and after CPB, we found no si gnificant difference in MAP, L/P ratio or base deficit between the gro ups, but both flux and pH(i) were significantly lower in group A compa red with group B. We conclude that neonates requiring aortic arch surg ery may be at particular risk of gut mucosal hypoxia both before and a fter operation.