[The comparison of hypnotic potency of nitrous oxide with that of sevoflurane: evaluation by the middle latency auditory evoked response].

In 10 consented patients (ASA I-II) we quantitated the hypnotic potencies of 0.7 MAC nitrous oxide and 0.7 MAC sevoflurane by measuring auditory evoked response (AER), and compared the hypnotic potency of nitrous oxide with that of sevoflurane at the same MAC. In each patient, measurements of AER waves were performed in the following three stages, 0.7 MAC nitrous oxide, 0.7 MAC sevoflurane and 0.7 MAC nitrous oxide after induction of anesthesia. Analysis of variance was used to compare the hypnotic potencies between two inhaled anesthetics. Pa and Nb latencies with sevoflurane were longer than those with nitrous oxide, and Pa and Nb amplitudes with sevoflurane were greater than those with nitrous oxide. However, we found that there were no statistical significances in our results. In conclusion, nitrous oxide exerts as much hypnotic effect as sevoflurane.