Direct current auditory evoked potentials during wakefulness, anesthesia, and emergence from anesthesia

Direct current auditory evoked potentials (DC-AEPs) are a sensitive indicat or of depth of anesthesia in animals. However, they have never been investi gated in humans. To assess the potential usefulness of DC-AEPs as an indica tor of anesthesia in humans, we performed an explorative study in which DC- AEPs were recorded during propofol and methohexital anesthesia in humans. D C-AEPs were recorded via 22 scalp electrodes in 19 volunteers randomly assi gned to receive either propofol or methohexital. DC-AEPs were evoked by bin aurally presented 2-s, 60-dB, 800-Hz tones; measurements were taken during awake baseline, anesthesia, and emergence. Statistical analysis included an alysis of variance and discriminant analysis of data acquired during these three conditions. About 500 ms after stimulus presentation, DC-AEPs could b e observed. These potentials were present only during baseline and emergenc e-not during anesthesia. Statistically significant differences were found b etween baseline and anesthesia and between anesthesia and emergence. In con clusion, similar effects, as reported in animal studies of anesthetics on t he DC-AEPs, could be observed in anesthetized humans. These results demonst rate that DC-AEPs are potentially useful in the assessment of cortical func tion during anesthesia and might qualify the method for monitoring anesthes ia in humans.