Quantitative topographical analysis of effects of single thiopental bolus on human electroencephalogram

The aim of present study was to characterize the topographical effect of thiopental on the EEG during induction of anesthesia. A multichannel (19 channels) digital EEG was recorded in 10 patients undergoing surgical treatment. The period during induction of anaesthesia before intubation was investigated in regard to peak frequency, amplitude, topography, and amplitude in conventional frequency bands. The main findings were a slowing of the EEG with a simultaneous increase of amplitude in the predominant EEG frequency (peak frequency) during induction. The topographical analysis showed a clear change of localization of the peak frequency in the occipito-frontal direction. Berger described the effect of thiopental on electrical cortical activity as early as 1933. Since then, many studies have investigated its influence on the EEG, but few have tried to characterize the effects of topographical changes in a quantitative way.