Intraoperative monitoring of evoked potentials.

Sensory EPs were recorded intraoperatively in 173 neurosurgical procedures (71 VEPs, 66 BAEPs, and 31 SSEPs) to evaluate the utility of this technique. EPs could be safely recorded in all cases, but the yield of useful results varied with each sensory modality. BAEPs were recorded reliably in 100% of the cases and intraoperative latency changes accurately predicted postoperative hearing deficits in 10%. Potential hearing deficits were detected in another 15%. BAEP changes were associated with brainstem dysfunction in only one case. VEP changes were difficult to interpret intraoperatively because of contamination by a high degree of variability and both false negative and false positive results. Changes in VEP amplitudes related to surgical manipulation of the optic chiasm were only suggested. SSEP changes were recorded reliably in only 75% of the cases and no correlations between SSEP changes and postoperative sensory function were established. Again, intraoperative amplitude attenuation of the SSEP waveform with surgical manipulation only suggested a potential sensory deficit. Intraoperative EP monitoring is a valuable technique that provides a functional analysis of the sensory nervous system during surgical procedures. Specific sensory stimuli and improved data analysis will increase the utility of this CNS monitor.