• Joanna C Murrell, Harry N de Groot, Evdokia Psatha, and Ludo J Hellebrekers.
• Department of Clinical Sciences of Companion Animals, University Utrecht, Yalelaan 8, NL-3508 TD Utrecht, The Netherlands.
• Am. J. Vet. Res. 2005 Jul 1; 66 (7): 1156-61.

ObjectiveTo investigate the middle latency auditory evoked potential (MLAEP) in awake dogs and dogs anesthetized with 2 concentrations of sevoflurane.Animals10 adult Beagles.ProcedureThe MLAEP was recorded while dogs were awake and anesthetized with sevoflurane (end-tidal concentration, 2.7% or 3.5%). Three needle electrodes were inserted SC, and click stimuli were delivered biaurally. Signal acquisition, averaging, and analysis were performed by use of computer software developed in-house. Signals were recorded for 128 milliseconds, and the responses to 1,024 stimuli were averaged. Waveforms from 10 recordings in each dog were averaged, and latencies of peaks were measured. Data acquired for awake dogs and dogs anesthetized with high and low sevoflurane concentrations were compared statistically.ResultsSevoflurane anesthesia attenuated the MLAEP so that only peaks P0, Na, and Pa could be identified. The MLAEP changes were maximal at the lower concentration of sevoflurane evaluated. The latencies of these peaks were significantly shorter in awake dogs, compared with values in anesthetized dogs. No difference in the peak latency was detected between the sevoflurane concentrations.Conclusions And Clinical RelevanceIn terms of CNS responsiveness, the effects of anesthesia with sevoflurane are similar to those of anesthesia with isoflurane. Data suggest that sevoflurane is not the inhalant agent of choice in a research setting where electroencephalographic measurements are to be recorded during anesthesia. The depression of the MLAEP waveform by sevoflurane also suggests that the MLAEP is not a suitable tool with which to monitor anesthetic depth during sevoflurane anesthesia in dogs.

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