Cortical responses to auditory stimuli during isoflurane burst suppression anaesthesia

The cortical responses to auditory stimuli were studied in 12 patients during isoflurane anaesthesia producing burst suppression (ETisof (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 pattern consisting of high-amplitude activity intermingled with suppressed background activity. In eight patients with burst suppression patterns, there was a strong cortical reactivity to the termination, not to the beginning, of auditory stimuli: 80 (20)% of all stimuli presented during EEG suppression 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 deep anaesthesia the brain retains its ability to respond to changes in the acoustic environment.