Cortical responses to auditory stimuli during isoflurane burst suppressionanaesthesia

The cortical responses to auditory stimuli were studied in 12 patients duri ng isoflurane anaesthesis producing burst suppression (ETisot (SD) 1.4 (0.2 ) vol.%). Earphones were used to give 3-s trains of auditory click stimuli (60 clicks, 20 clicks per second, 80 dB, 0.1 ms) at irregular intervals. In 10 patients, the electroencephalography (EEG) showed a burst suppression p attern consisting of high-amplitude activity intermingled with suppressed b ackground activity. Tn eight patients with burst suppression patterns, ther e was a strong cortical reactivity to the termination, not to the beginning , of auditory stimuli: 80 (20)% of all stimuli presented during EEG suppres sion evoked high amplitude cortical response, offset-burst. The latency of these auditory offset evoked bursts was 540 (60) ms. Auditory offset evoked bursts suggest that in spite of cortical suppression during deer anaesthes ia the brain retains its ability to respond to changes in the acoustic envi ronment.