gms | German Medical Science

Objective: During surgeries that put the visual pathway at risk of injury, continuous monitoring of visual function is desirable. However, there is no consensus in the literature on the usefulness of intraoperative monitoring of visual evoked potentials (VEPs). Only recently have stimulating devices with high luminance been introduced, which we tested in a series of patients.

Method: We included 30 patients under total intravenous anesthesia for intraoperative VEP monitoring. Flash stimulation was provided by 15 red light emitting diodes with a frequency of 1.1 Hz. VEPs were recorded at the sites O1, O2, Oz and against Fz, Cz and linked A1 and A2 (A+). We analyzed the stability of the VEP features N75 and P100 and also postoperative visual function.

Results: Intraoperative VEP monitoring was feasible in 25 of 30 patients (83%). The other 5 patients had severe preoperative visual dysfunction. The median amplitude of N75 was 2.5µV (range ?0.8-7.7µV) and the median latency 84ms (57-142ms). The median?amplitude and latency of P100 was 1.9µV (0.5-7.0µV) and 102ms (75-161ms). Of the recording channels, Oz/A+ provide the largest?number of stable VEPs (34 of 47, 72%, CI [57%-84%]). Of the 21?patients without VEP amplitude change, 3 showed improved visual?function postoperatively, 15 showed no change and 3 developed hemianopsia. Transient VEP decrease was observed in 2 patients, but visual function was preserved. Permanent VEP decrease was seen in 2 patients without new postoperative visual impairment.

Conclusions: Intraoperative VEP monitoring was feasible in all patients without severe preoperative visual impairment. VEPs were not sufficiently sensitive to predict visual field defects.