Purpose: Visual Evoked Potentials (VEPs) are considered an unreliable modality. Cited difficulties include anesthetic sensitivity, imprecise electrode placement, and insufficient quality of electrodes. This review investigates these variables and presents a case where reliable recordings were obtained. Methods: Intraoperative Monitoring (IOM) VEP recordings were undertaken in a surgical clipping of a left MCA aneurysm in a patient with intact vision. Preoperative visual function was normal and the visual pathways not at risk during the procedure, allowing electrode positioning and changes in anesthesia to be studied. EEG, MEP, and SSEP monitoring were performed. Results: Baseline VEPs were reliable and present from individual eye stimulation. When the left scalp flap was retracted forward, the left VEP became unobtainable. The right VEP remained stable. During clipping of the aneurysm, EEG became discontinuous after propofol bolus and infusion increase. The right VEP remained consistent with baseline. When the scalp flap was replaced, the left VEP electrode was repositioned and the left VEP returned to baseline. Conclusions: VEP changes were associated with changes in electrode position, but not with changes in anesthesia or surgical conditions. Our findings suggest with good electrode positioning, VEPs can be obtainable, reproducible, and may be useful for intraoperative decision making.
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