[Effect of enflurane on human somatosensory evoked potentials: differences between specific and nonspecific...

The effect of enflurane on somatosensory evoked potentials (SEP) was investigated in nine gynecological patients under nitrous oxide-enflurane anesthesia. SEPs were obtained from electrodes placed on the scalp C4 and earlobes by median nerve stimulation contralateral to the recording site. SEPs taken in a control study without enflurane consisted of six components; P12, N17, P23, N31, P50, and N65. Components N17, P23, N31, and P50, thought to be specific SEP responses, showed a dose-dependent increase in latencies under enflurane while P12, the initial SEP components, did not show any significant changes throughout the experiment. The longer the latency for a given response component, the greater was the increase in latency seen under enflurane anesthesia. On the other hand, N65, assumed to be a nonspecific SEP response, was completely lost with inhalation of 0.5 MAC or more of enflurane. However, the peak-to-peak amplitude between P23 and N31 was enhanced dose-dependently with enflurane up to 1.5 MAC. These results suggest that, at clinically effective doses, enflurane may inhibit nonspecific projection pathways while enhancing the primary cortical sensory area, and this enhancement may be responsible for provoking convulsive seizures under enflurane anesthesia.