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SummaryEphedrine, a sympathomimetic drug, may stimulate the central nervous system via its amphetamine-like effect under light general anaesthesia. We compared the effect of ephedrine on auditory-evoked potentials with that of etilefrine, a sympathomimetic drug that lacks an amphetamine-like effect, in patients undergoing abdominal surgery under general anaesthesia with 67% nitrous oxide in oxygen and epidural blockade. Ephedrine (0.08 mg.kg À1 intravenously) signi®cantly decreased the latencies of Nb and P 1 from 49.5 (4.2) [mean (SD)] and 63.9 (9.1) ms to 45.9 (4.2) and 59.0 (9.9) ms, respectively; whereas etilefrine (0.02 mg.kg À1 intravenously) caused no signi®cant changes in these potentials. In addition, the latencies of Nb and P 1 before drug administration were positively correlated with patient age. These ®ndings suggest that ephedrine can cause excitation of the central nervous system during light general anaesthesia, and that auditory-evoked potentials may be a sensitive indicator of the depth of anaesthesia.

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