Visual Evoked Potential for Monitoring the Depth of Anesthesia

Abstract

Relationship between the latency of visual evoked potential (VEP) and the depth of anesthesia was investigated in the surgical patients in order to evaluate the applicability of VEP to monitor the depth of anesthesia. The VEP was recorded with a standard EEG electrode from the midline parietal region (V-potential) with reference to both earlobes linked to the ground. The array of light-emitting-diodes (LED) mounted in opaque goggles was used to stimulate both eyes simultaneously and photic stimuli were delivered at random inter-stimulus intervals with uniform distribution ranged from 2 to 5 seconds. Fifty segments of data were averaged to estimate the Pmax latency, i. e., the latent period from the photic stimulus to the maximum positive peak.
It was observed that the Pmax latency increased following the administration of anesthesia and returned to the preanesthetic value after the recovery of anesthesia. The Pmax latency showed an increase in proportion to the inspiratory concentration of enflurane gas. The latency of Pmax was also prolonged with addition of the neuro-lept-anesthesia (NLA) and with decrease in blood pressure during enflurane anesthesia. In case of patient with hypoglycemia, the Pmax latency increased drastically, which suggests an extreme sensitivity to anesthesia during hypoglycemia. It is concluded that the observation of the latency of VEP is found to be very useful for monitoring the depth of anesthesia and the vital conditions of the patients under anesthesia.