SOMATOSENSORY-EVOKED POTENTIALS DURING ISOFLURANE ANESTHESIA

Short latency somatosensory evoked potentials (SEPs) to median nerve s timulation during isoflurane anaesthesia were recorded in 12 elective- surgery patients. The effect of isoflurane on the shape, amplitude and latency of SEPs was evaluated. SEPs were recorded at awake, 1 MAC, 1. 5 MAC, at electroencephalogram (EEG) burst suppression and at continuo us suppression levels. Finally, SEPs were recorded when anaesthesia wa s lightened back to 1 MAC. The peak latency and amplitude of the first cortical N-20 wave were measured. The latencies increased with increa sing isoflurane concentrations. At high concentrations only an almost monophasic N-20 wave was recorded, reduced in shape and amplitude. No specific changes could be correlated with the burst suppression or sup pression patterns. This suggests that EEG and SEP generators are diffe rently affected with increasing isoflurane concentration. The results indicate that SEPs can also be recorded in drug-induced EEG suppressio n.