Somatosensory, visual and brainstem auditory evoked potentials were recorded in 10 unpremedicated patients anaesthetized with isoflurane in oxygen. Recordings were made at 0.5%, 1.1% and 1.65% (six patients) end-tidal isoflurane concentration. There were statistically significant increases in the latencies of the somatosensory (N20), visual and brainstem auditory potentials (waves III and V) with increasing concentrations of isoflurane. The central conduction time was prolonged. Amplitudes of the somatosensory and visual potentials were reduced with increasing concentrations of isoflurane. The effects of isoflurane on evoked potentials are similar to those of halothane and enflurane. It is possible that changes in evoked potential measurements may be useful as a neurophysiological indicator of anaesthetic depth.
SummaryThe effict.7 of fentanyl or diazepam on somatosensor?; visual and brainstem auditory evoked potentials were studied in 13 healthy patients schcduledjor elective surgery. Following control recordings of evoked potentials. either diazepam 20 mg or /tntangl200 p g M'US administered intravenously. Evokedpotentials were then recorded twice in the subsequent hour. N o significant changes occurred in the latenry or amplitude nf somatosensory, visual or brainstem auditory evoked potentials. Although dose-related changes in evoked potential latencies and amplitudes have been demonstrated with both the inhalational and intravenous anaesthetics, these changes did not occur with diazepam or .fentanyl used alone. An unaesthetic technique based on these two drugs would be suitable uhen intra-operative evoked potential monitoring is required to asse~s ischaemia and preservation of evoked responses.
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