CARDIOPULMONARY BYPASS TEMPERATURE, HEMATOCRIT, AND CEREBRAL OXYGEN DELIVERY IN HUMANS

Background. The neurologic effects of warm heart operations is a subje ct of popular interest. The purpose of this study was to examine the a dequacy of cerebral oxygenation during normothermic cardiopulmonary by pass and better define the relationship between hematocrit, temperatur e, and brain oxygen delivery. Methods. Cerebral blood now, metabolic r ate, and oxygen delivery were measured in 60 patients randomized to no rmothermic (37 degrees C) or hypothermic (27 degrees C) cardiopulmonar y bypass. The nitrous oxide saturation technique of Kety and Schmidt w as used for cerebral blood now determinations. Both temperature groups underwent moderate (31%) hemodilution. Results. During normothermic c ardiopulmonary bypass, cerebral blood now increased secondary to hemod ilution and decreased cerebral vascular resistance; a normal matching of oxygen demand and delivery was maintained. During hypothermic bypas s, hemodilution and hypothermia had essentially equal, opposing effect s on cerebral vascular resistance and blood now. With hypothermia, bra in oxygen demand and delivery were both reduced but not closely couple d. Conclusions. From the standpoint of global cerebral perfusion and o xygenation, our data support the practice of ''warm'' heart operations . It clarifies the marked influence of hematocrit on cerebral blood no w and delineates the interaction of temperature and hematocrit on cere bral oxygen delivery. It also suggests that additional investigation t o better define ''temperature-appropriate'' hemodilution during cardio pulmonary bypass is indicated.