Brainstem auditory evoked potential monitoring - When is change in wave V significant?

Background: The probability of hearing loss during cerebellopontine angle ( CPA) surgery can be reduced by using brainstem auditory evoked potential ( BAEP) intraoperative monitoring ( IOM). A wave V latency prolongation of 1.0 milliseconds or amplitude decrement of greater than 50% is arbitrarily considered the point when damage to hearing occurs. Objective: To determine the accuracy of wave V changes in predicting hearing impairment. Methods: Patients undergoing BAEP IOM for surgery in the CPA region were evaluated. The greatest wave V latency and amplitude change was determined. Patients were divided into four groups depending on degree of change of wave V: Group 1 consisted of minimal change, whereas Group 4 was permanent loss of wave V. The frequency of hearing loss in each group was compared. Results: Data from 156 patients were reviewed. When all patients were analyzed, the frequency of hearing loss was not significantly different between the groups. When patients with CPA tumor were excluded, a significantly higher number of patients in Group 4 had hearing loss. Analysis of the patients with CPA tumor showed no difference in the frequency of hearing loss in any of the groups; even a large number ( 50%) of Group 1 patients had hearing impairment. Conclusions: During brainstem auditory evoked potential intraoperative monitoring, the type of surgery is important when interpreting significance of changes of wave V. For non - cerebellopontine angle tumor surgery, hearing loss occurs usually only with permanent loss of wave V; much smaller changes may be important in cerebellopontine angle tumor surgery.