Changes in the electroretinogram and visual evoked potentials during general anaesthesia using enflurane.

Abstract

Fourteen female patients 27.7 +/- 10.0 years of age were studied by electrophysiological means before and during general anaesthesia. A mixture of thiopentone sodium, enflurane and nitrous oxide was used for anaesthesia. Electroretinogram (ERG) and visual evoked potentials (VEP) were recorded with electrodes placed on the lower lid and scalp and an averaging technique was used. The recordings were made under standard conditions with the pupils dilated, the eyes adapted to the dark and after 15-20 min stable anaesthesia. The latency of the a-wave did not change, whereas the b-wave was delayed (P less than 0.01). The amplitude of the a-wave tended to decrease; however, an increase of amplitude was also present. Therefore the change was not significant. The b-wave was unchanged. Changes induced by anaesthesia were often noted in the shape of P130, where a change from V to W-form took place or the reverse. The latencies of the late components N180 and P220 were increased during anaesthesia (P = 0.006 and P = 0.001, respectively). No statistically significant change occurred in the N180 and P220 amplitudes. The amplitudes of N60 and P130 became smaller (P = 0.002 and P = 0.0003, respectively) during anaesthesia. The effect of enflurane on the components of the VEP seems to indicate a cortical site of action.