[Power spectral analysis of EEG during simple deep hypothermia under ether anesthesia]

Power spectral analysis of electroencephalogram was performed during simple deep hypothermia under ether anesthesia, compared with that during hypothermic cardiopulmonary bypass under morphine anesthesia. In ether anesthesia group, EEG isoelectricity developed at average esophageal temperature of 27.2 degrees C which is higher than the temperature previously reported. This remarkable depression of the EEG may be due to deep ether anesthesia, because severe hypotension episodes were not associated with this and no neurological complication was noticed post-operatively. In cardiopulmonary bypass group, EEG activity persisted throughout the procedures even at the lowest esophageal temperature reached of 22.3 degrees C. In ether anesthesia group, the temperature at which EEG activity reappeared correlated with the duration of circulatory arrest. During simple deep hypothermia under ether anesthesia, the EEG is not useful to detect brain ischemia during cooling period, because EEG activity was lost in the early course of cooling, but during rewarming period the EEG demonstrated depression of cerebral function due to total circulatory arrest.