Influence of dose and duration of isoflurane anesthesia on the auditory brainstem response in the rat

OBJECTIVE: Isoflurane anesthesia can have significant effects on processing of sounds at the peripheral and central levels, manifesting in changes in auditory-evoked potentials. The current study tested whether duration of isoflurane anesthesia changes thresholds, amplitudes, and latencies of the auditory brainstem response (ABR). DESIGN: The study tested ABRs in a rat animal model under isoflurane anesthesia. Study variables were duration of isoflurane anesthesia, stimulus frequency, stimulus level, and the dose of isoflurane. Rats were anesthetized with 1.5% or 2% isoflurane. ABRs were collected from 90 to 5 dB SPL at 5-40 kHz. Three full ABR series were collected over a 105-minute period. Thresholds were assigned, and ABR wave amplitudes and latencies were measured at each stimulus frequency and level. STUDY SAMPLE: Ten Sprague-Dawley rats were tested in a repeated measures design. RESULTS: Statistical analyses revealed no significant effects of dose or duration on threshold, but a series of significant interactions between test variables for the amplitude and latency measurements. CONCLUSIONS: In the rat, dose and duration of isoflurane anesthesia induced inconsistent changes in latency and amplitude of the ABR. At 40 kHz, isoflurane dose had more powerful effects on latency and amplitude than occurred at other frequencies.