[Human flash visually evoked cortical potentials under different levels of halothane anesthesia]

Flash visually evoked cortical potentials (FVECPs) were recorded in 13 surgical patients under different levels of halothane anesthesia, altering the rate of stimulus frequency from 0.5 Hz to 10 Hz. VECPs were obtained in the awake state under premedication with atropine sulphate, and at end-tidal halothane concentrations of 0.38%, 0.75%, 1.13% and 1.5%. The peak latency of P1 (the major positive component with a latency of about 100 msec) progressively increased from 116.7 +/- 3.3 msec (mean +/- SE) in the awake state to 124.3 +/- 6.3 msec, 136.5 +/- 5.2 msec, 151.5 +/- 5.2 msec and 166.3 +/- 8.7 msec with increasing halothane concentration. Significant reductions in P1 amplitude were observed to 2 Hz, 5 Hz and 10 Hz stimuli, whereas there were no significant changes in amplitude to 0.5 Hz and 1 Hz stimuli. P1 amplitude plotted against stimulus frequency had a maximum at 10 Hz in the awake state. This curve gradually and preferentially attenuated at higher frequencies as halothane concentration increased.