The effects of volatile anesthetics on the relative amplitudes and latencies of spinal and muscle potentials evoked by transcranial magnetic stimulation

Study Design. The effects of halolhane, enflurane, or isoflurane on moior-evoked potentials via trenacraniol; magnetic stimulation were Investigated in cats. Time and dose effects on musclB potentials and spinal potentials were determined by measuring relative changes in amplitudes and latencies.Method!. In 16 cots, muscle potentials end spinal potentials were evoked tranecranially using magnetic stimulation. Potentials were recarded every Z minutes for 10 minutes et snd-lidal anesthetic concentrations of I 0.25%, 0, 5%,'0.75%, or 1.0%, end for 10 minutes after agents were removed, Results, These anesthetics significantly attenuated the amplituda, but not the latency of muscle potentials. 1 Effects were reversible end time and dose dependent. In contrast, these agents had little or no effect on ampli* tudes or latencies; of spinal potentials. Conclusions. Monitoring intraoperstlve changes in spinal potentials may.provide useful information regarding motor pathway assessment, because anesthetics liave minimal effects on spinal potentials, whereas this is not so for muscle potentials.