Factors that limit the use of flash visual evoked potentials for surgical monitoring.

A study was conducted comparing the incidence with which the N2/P2/N3 was obtained after flash VEP in 3 groups: anterior visual pathway lesions, non-tumor craniotomies and non-cranial surgery. These groups allowed evaluation of the effects of anesthesia, visual pathway lesions and craniotomy on the stability of the flash VEP. It was found that the latency was not significantly affected in the 3 groups, whereas the incidence of obtainable peaks and the amplitudes were adversely affected by anesthesia, cranial surgical manipulation and especially by the presence of a visual pathway lesion. These adverse effects were so marked that the application of flash VEP for intraoperative monitoring seems of little use.