A PROSPECTIVE, RANDOMIZED COMPARISON OF CEREBRAL VENOUS OXYGEN-SATURATION DURING NORMOTHERMIC AND HYPOTHERMIC CARDIOPULMONARY BYPASS

Recent reports have described cerebral venous oxygen desaturation duri ng and after rewarming from hypothermic cardiopulmonary bypass. Additi onally, patients undergoing normothermic cardiopulmonary bypass may be at higher risk for neurologic injury. This study was designed to dete rmine whether patients undergoing normothermic cardiopulmonary bypass are at increased risk for sustained cerebral desaturation. Fifty-two p atients undergoing first-time coronary artery bypass grafting were ran domized to receive normothermic (37 degrees C, n = 26) or hypothermic (27 degrees C, n = 26) cardiopulmonary bypass. The anesthetic was stan dardized and alpha-stat pH management was used. A 4F oximetric cathete r was placed in the jugular bulb and cerebral venous and radial arteri al blood were sampled. Oxygen partial pressure and saturation were mea sured at six intervals from cerebral venous blood and from radial arte rial blood. Patients receiving normothermic cardiopulmonary bypass had lesser values of oxygen partial pressure and saturation in cerebral v enous blood than patients subjected to hypothermia during the first 40 minutes of bypass. Cerebral venous desaturation (oxygen saturation in cerebral venous blood of 50% or less) was observed in 54% of patients in the normothermic group and 12% of patients in the hypothermic grou p during cardiopulmonary bypass. In the normothermic group, cerebral d esaturation occurred primarily in early bypass (14 of 26). The three e pisodes of desaturation in the hypothermic group occurred during rewar ming. During cardiopulmonary bypass, the arteriovenous oxygen content difference was greater in the normothermic group than in that in the h ypothermic group, suggesting higher oxygen consumption. Differences in glucose utilization during early cardiopulmonary bypass between the g roups was also detected. One patient in the hypothermic group had an e mbolic stroke and subsequently died. There were no other perioperative strokes or deaths in the study population. The present study demonstr ates that patients undergoing normothermic cardiopulmonary bypass are at greater risk for cerebral desaturation. Because it is a global asse ssment, cerebral venous oxygen saturation may be insensitive to focal ischemic events. It remains to be seen whether these differences in ce rebral physiologic states translate into differences in clinical outco me.