Effect of stimulus pulse duration on intraoperative somatosensory evoked potential (SEP) monitoring

The effect of the stimulus duration on the amplitude and latency of intraop erative somatosensory evoked potential (SEP) was studied in 30 patients wit h idiopathic scoliosis undergoing surgery. Constant current square-wave ele ctrical stimulation was applied to the posterior tibial nerve at a rate of 5.1 Hz. The effects of both the pulse duration and the stimulus current den sity on the intraoperative SEP were evaluated. Amplitudes and latencies of SEP were analyzed by one-way parametric analysis of variance. SEP signal re cording was found to be difficult if the stimulus duration was less than 0. 05 ms. The stimulus duration had no significant effect on the latencies of the SEP, but the amplitude of the SEP showed significant changes with diffe ring stimulus durations. The SEP amplitudes were found with significant inc reases in pulse durations less than 0.3 ms. Stimulus pulse duration has a s ignificant effect on SEP amplitude, and this should be taken into considera tion during intraoperative SEP monitoring. A pulse duration of 0.3 ms is re commended for SEP using posterior tibial nerve stimulation.