DETERMINANTS OF CEREBRAL PERFUSION DURING CARDIOPULMONARY BYPASS

The risk of postoperative neurologic dysfunction in patients undergoin g cardiac surgery remains high despite continued improvements in myoca rdial protective strategies. Part of this neurologic morbidity can be attributed to patients' increased age and underlying pathology, but ot her factors adversely affecting cerebral blood flow and cerebral metab olism during cardiopulmonary bypass may also contribute. Particulate m icroembolization during cardiopulmonary bypass appears to be a major c ause of postoperative neurologic dysfunction and the pH-stat method of carbon dioxide management during hypothermia may potentiate neurologi c damage by allowing a greater embolic load to be delivered to the bra in. Echocardiography and transcranial Doppler methods may contribute t o reducing the incidence of cerebral embolization by recognizing the t iming and number of microemboli. Although hypothermia confers cerebral protection, rewarming may unmask and perhaps potentiate any ischemic damage that occurred with embolization during hypothermia. Both the de gree and speed of rewarming may be important factors contributing to t he extent of ischemic damage and ultimately neurologic function. In ad dition, many other factors related to cardiopulmonary bypass can alter cerebral perfusion and metabolism, such as nonpulsatile flow, hemodil ution, pressure autoregulation, anesthetic and cerebroprotective drugs , and the neuroimmune response to bypass. In this review, the major fa ctors affecting cerebral blood flow during cardiopulmonary bypass are discussed and their relative importance evaluated with regard to posto perataive neurologic function. Copyright (C) 1996 by WB. Saunders Comp any.