CEREBRAL BLOOD-FLOW DURING LOW-FLOW HYPOTHERMIC CARDIOPULMONARY BYPASS IN BABOONS

Background: Neurologic injury after cardiopulmonary bypass (CPB) is a frequent and devastating complication of cardiothoracic surgery. Disor dered cerebral hemodynamics during CPB has been implicated as an impor tant factor in the etiology of these injuries. Evidence of disordered cerebral hemodynamics includes reports of a progressive time-dependent decrease in cerebral blood now (CBF) during stable full-flow CPB. Low -flow hypothermic CPB has become a preferred technique for the managem ent of pediatric patients undergoing surgical repair of complex cardia c lesions. Because CBF is already substantially reduced with the onset of low-flow CPB, we determined if a similar progressive decline in CB F occurs during the low-flow state. Methods: after induction of genera l anesthesia in seven baboons, CPB was instituted. alpha-Stat manageme nt of arterial blood gases was used. Animals were cooled at a pump flo w rate of 2.5 l.min(-1).m(-2) until tympanic membrane temperature decr eased to 18 degrees C. CPB flow was then reduced to 0.5 l.min(-1).m(-2 ) and maintained constant for at least 77 min. Thereafter, CPB now was increased to 2.5 l.min(-1).m(-2) and baboons rewarmed to normal tempe rature. CPB was discontinued after return of cardiac function. CBF was measured before, during and after CPB by washout of intraarterial xen on 133. Results: Low-flow CPB resulted in a decrease in CBF to about 5 0% of the prebypass rate and about 30% of the value measured during fu ll-flow CPB. Sequential measurements of CBF at 30-min intervals during low-now CPB showed no time-dependent change in cerebral perfusion. Co nclusions: Although systemic flow is reduced to 20% of full-flow durin g low-flow CPB, CBF reduced by half is disproportionately preserved re lative to systemic flow. Furthermore, there is no time-dependent chang e in CBF under these low-flow conditions.