Synaptic effects of halogenated anesthetics on short-latency SEP.

We evaluated the effects of different stable end-tidal concentrations of isoflurane, enflurane, or halothane on short-latency somatosensory evoked potentials recorded during general anesthesia. Isoflurane and enflurane significantly enhanced the P22 over the pre-central scalp, whereas the parietal N20 amplitude did not increase. The P22 increase did not occur with halothane, which indicates that the P22 changes are a specific effect of certain anesthetics, probably related to their influence on synaptic events. At the subcortical level, isoflurane and enflurane increased significantly the N13 peak latency and decreased the interval between the N13 peak and P14 peak, which implicates interference with synaptic transmission at the spinal level. Halothane had no effect at the spinal level. All three anesthetics significantly increased the central conduction time.