Changes in cortical electrical activity during induction of anaesthesia with thiopental/fentanyl and tracheal intubation: a quantitative electroencephalographic analysis

Background. There are regional differences in the effects ofanaesthetics agents and perioperative stimuli on the EEG. Westudied the topography of the EEG during induction of anaesthesiaand intubation in patients receiving thiopental and fentanylto document regional electrical brain activity. Methods. EEG was recorded in 25 patients in the awake state,after pre-medication, during induction, at loss of consciousnessand after intubation. Eight bipolar recordings were made andthe relative power of the frequency bands delta, theta, alpha,and beta were used (after z-score transformation for age) tomeasure changes in regional EEG activity. Results. Noxious stimulation during tracheal intubation partiallyreversed the slowing of the EEG caused by anaesthesia. Duringinduction of anaesthesia alpha activity was most reduced intemporal and occipital regions. The most prominent EEG changesafter intubation were an increase in alpha and a decrease indelta power (P<0.001). The largest changes were in the frontaland temporal leads for alpha and in the frontal and centralleads for delta. Heart rate and arterial pressure remained constantduring intubation. Conclusions. Changes in alpha and delta power were identifiedas the most sensitive EEG measures of regional changes in electricalbrain activity during anaesthesia and noxious stimulation. Br J Anaesth 2004; 92: 33–8