Correlation between latency and amplitude of peak V in the brainstem auditory evoked potentials: intraoperative recordings in microvascular decompression operations.

Intraoperative prolongation of the latency and decrement of the amplitude of peak V of brainstem auditory evoked potentials (BAEP) were studied in 38 microvascular decompression operations in which prolongation of the latency of peak V exceeded 1.0 msec. Postoperative hearing tests of all patients were compared with their preoperative hearing tests. Postoperative hearing loss was unrelated to the maximum prolongation of latency, but the amplitude decreased to lower values in patients with postoperative hearing loss compared to patients whose postoperative hearing was unchanged (P < 0.05). Twelve (32%) of 38 patients whose latency of peak V was prolonged more than 1.0 msec and 11 (61%) of 18 patients whose amplitude of peak V decreased more than 40% during the operations had decreased hearing postoperatively. In all patients, a prolongation of the latency of peak V was always accompanied by a decrease in the amplitude of peak V. The decrement of the amplitude was greater in the patients with decreased postoperative hearing thresholds than in the patients with unchanged postoperative hearing thresholds. The results of this study indicate that it would be valuable to monitor changes in the amplitude of peak V of BAEP in addition to monitoring the latency of peak V during operations where the VIIIth cranial nerve is manipulated.