Automated monitoring of brainstem auditory evoked potentials in the operating room

We monitored brainstem auditory evoked potentials in 112 patients undergoing retromastoid craniectomies for microvascular decompression. To provide information on latency changes as quickly as possible, we implemented a block averaging technique of data acquisition with automatic tracking of wave V latency, which is the most clinically useful information. A change in peak latency probably due to surgical manipulation was observed in 63% of the patients, and the change could be at least partially corrected by modification of surgical technique. Twenty percent ot the 89 patients who underwent preoperative and postoperative audiometric testing showed a postoperative hearing decrement. Some patients had large intraoperative increases in latency without suffering postoperative hearing deficits, and some incurred hearing deficits even though the intraoperative latency increases were relatively small. However, patients whose brainstem auditory evoked potentials were lost during surgery, even temporarily, were likely to have postoperative hearing decrements. Patients who had deficits tended to have slightly greater increases in latency than patients without deficits, but the difference in the mean increases ot the two groups was not statistically significant. Most of the deficits were small, and all resolved over time.