Topographic analysis of the effects of isoflurane anesthesia on SEP

Isoflurane anesthesia induces a striking increase in the P22 potential recorded over the precentral scalp whereas the amplitude of the N20 is reduced. It is not known whether the increased "P22" enhanced by isoflurane arises from the same generator as the small precentral P22 potential recorded in the normal awake subject. Multi-channel recordings of SEP before and during isoflurane anesthesia were performed in 13 normal subjects. Isopotential topographic maps showed that isoflurane did not change the distribution of the precentral "P22" despite its clear amplitude increase. Our data confirm that isoflurane enhances the precentral P22 and that the enhanced "P22" arises from the same generator as the P22 recorded before isoflurane anesthesia.