Effects of stimulus intensity and duration on posterior tibial nerve somatosensory-evoked potential patterns obtained under anesthesia.

Abstract

This study analyzed systematic changes in stimulus intensity and duration on the latencies and amplitudes of somatosensory-evoked potential peaks obtained upon posterior tibial nerve stimulation of orthopedic patients under anesthesia. To examine the effects of systematic stimulus changes on somatosensory-evoked potential patterns and to compare the sensitivity of different peaks. Previous studies primarily examined the effects of either stimulus intensity or stimulus duration but not their interactions. Nine orthopedic patients were tested using three stimulus intensities and three stimulus durations. Five peak latencies and four amplitudes were measured. Data consisted of frequency of peak occurrences under each condition and analyses of variances of peak latencies and amplitudes. Three latencies yielded stable findings (P40, N50, P60). Peak latencies under anesthesia were not affected by stimulus intensity or duration. Amplitudes, however, were affected differentially. P40-N50 increased with increases in stimulus intensity or stimulus duration, but no significant interaction effects were found. N50-P60 showed no significant changes associated with stimulus intensity or duration. Under combined isoflurane/nitrous oxide anesthesia, somatosensory-evoked potential patterns obtained upon stimulation of the posterior tibial nerves showed no significant changes in major peak latencies with changes in stimulus intensity or duration. However, changes in amplitude were found. Stimulus intensity-duration interaction effects were observed, described, and interpreted.