BRAIN-DAMAGE FOLLOWING LOW-FLOW CARDIOPULMONARY BYPASS IN PIGS

Reduction of pump flow during cardiopulmonary bypass (CPB) reduces the formation of microemboli and trauma to the blood components, reduces both rewarming of the heart and the noncoronary collateral flow, and i mproves surgical exposure. Recent studies indicate that a reduction in pump flow, even at normothermia, does not increase the incidence of p ostoperative cerebral dysfunction. We examined the cerebral consequenc es of 2 h of normothermic CPB in pigs carried out at pump flows of eit her 70 ml/kg per min or 50 ml/kg per min, and compared the results wit h those of a nonperfused control group. We measured the regional cereb ral glucose metabolism and the regional capillary diffusion capacity s imultaneously in ten different brain regions. Brain morphology, the bl ood-brain barrier permeability to serum proteins and the regional cere bral water content were also determined in the same animals. Glucose m etabolism decreased significantly in both CPB groups (P < 0.001), and significant differences were found between the capillary diffusion cap acities of the three groups (P < 0.05), with decreases in eight out of ten brain regions examined in the 50 ml/kg per min group. The results indicate that a reduction of pump flows from 70 ml/kg per min to 50 m l/kg per min is deleterious to the brain, and that a pump flow of 70 m l/kg per min itself has an injurious effect, when normothermic CPB is carried out for 2 h without the use of vasoactive drugs to maintain th e blood pressure. Mean arterial blood pressure (MAP) rather than pump flow seemed to determine the adequacy of the cerebral perfusion.