Hypothermia plus thiopental: prolonged electroencephalographic suppression

Duration of EEG suppression was compared to three groups of patients undergoing hypothermic cardiopulmonary bypass (CPB) at 25-30 degrees C under halothane-nitrous oxide anesthesia. Group I (n = 8) received three doses of thiopental (8 mg/kg i.v.): 1) for induction of anesthesia, 2) immediately after the institution of CPB, and 3) just after emergence from CPB. Group II (n = 5) received no thiopental. Group III (n = 4) received thiopental, 8 mg/kg administered intravenously, during CPB only. An unexpectedly prolonged duration of EEG suppression (26.1 min) was noticed in Group I patients with thiopental and hypothermia in combination, as compared with 4.8 min of suppression in Group II patients during hypothermic CPB without thiopental. To rule out a possible cumulative effect of thiopental administration, Group III patients were studied. With only a single dose of thiopental, administered during CPB, 29.3 min of EEG suppression was noticed. Mild cardiovascular depression occurred with thiopental administration during induction of anesthesia, whereas mild-to-moderate depression was associated with thiopental administration following emergence from CPB. It appears that thiopental and hypothermia, when administered in combination in modest doses during CPB, result in profound depression of cerebral electrical activity and presumably cerebral metabolism.