Enhanced stability of somatosensory evoked potentials attained in the median nerve by using temporal electrodes for intraoperative recording in patients in the semisitting position.

Object: Findings published in case reports indicate that monitoring of median nerve somatosensory evoked potentials (MN-SSEPs) is unreliable in patients who undergo surgery while in the semisitting position due to the occurrence of changes in the potentials that are unrelated to neurological damage. The present study was designed to test the hypothesis that in these patients MN-SSEPs are more stable when recording electrodes are placed over the temporal region.

Methods: In 30 patients who underwent surgery in the semisitting position, MN-SSEPs were recorded intraoperatively by using electrodes placed over the temporal region as well as those placed at conventional recording sites. The authors analyzed MN-SSEP amplitudes and latencies at different recording sites and at distinct steps of the monitoring procedure. In 10 of the 30 patients a clinically significant attenuation (> 50%) of MN-SSEP amplitude was observed at conventional recording sites and this was obviously not related to neurological damage. In contrast, no significant changes were observed in MN-SSEPs recorded from electrodes located over the temporal region.

Conclusions: In patients who undergo surgery in the semisitting position, the use of additional recording electrodes placed over the temporal region makes intraoperative MN-SSEP monitoring less prone to false-positive alarms and thus enhances the reliability of intraoperative MN-SSEP monitoring.