ENFLURANE ANAESTHESIA CAUSES GRADED CHANGES IN THE BRAINSTEM AND EARLY CORTICAL AUDITORY EVOKED RESPONSE IN MAN

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Abstract
The effect of increasing end-tidal enflurane concentration on the auditory evoked response was studied in 6 patients. After a standard induction, anesthesia was maintained with 70% N2O in O2 and the end-tidal enflurane concentration was increased gradually from 0-1% over a period of 30 min. The averaged auditory evoked response was derived from the EEG and measurements were made of the latencies and amplitudes of waves I, III, V, Pa and Nb within the auditory evoked response. The latencies of all waves and the interpeak latencies I to V and III to V showed significant linear increases and the amplitudes of Pa and Nb showed significant linear decreases with increasing end-tidal enflurane concentration. These results could not be explained by changes in deep body temperature or end-tidal CO2 concentration. The study demonstrated a dose-related direct effect of enflurane on the brainstem and early cortical components of the auditory evoked response.