Hypothermia after cardiopulmonary bypass in man: amelioration by nitroprusside-induced vasodilation during rewarming

The incidence, time course, and magnitude of hypothermia following apparently adequate rewarming from hypothermic cardiopulmonary bypass (defined as a nasopharyngeal temperature [NPT] of 37 C) were studied in 20 adult patients (Group I). In each patient a decrease in NPT (averaging 2.6 +/- .2 C) occurred during the 80-min intraoperative postbypass period. The NPT had stabilized approximately 45 min after the end of bypass. Eight additional patients (Group II) received pharmacologic vasodilation with nitroprusside during the rewarming period. Pump flow was increased as nitroprusside was infused to maintain mean arterial pressure greater than or equal to 70 torr. Group II patients maintained NPT significantly better in the postbypass period than did Group I patients (NPT decrease of 1.5 +/- .4 C, P < 0.01, a 42 per cent improvement). As in Group I, NPT in Group II had stabilized 45 min after bypass. Ambient air temperatures between 18 and 23 C had no effect on NPT decrease. Presumed peripheral heat delivery was found to be greater in Group II. It is concluded that postbypass NPT decreases occurred in all patients, but that these decreases were significantly lessened by pharmacologic vasodilation plus deliberately increased pump flow during rewarming on bypass.