Power spectrum correlates of changes in consciousness during anesthetic induction with enflurane

In order to correlate electroencephalogram (EEG) changes during anesthetic induction with level of consciousness, four-channel parasagittal EEG recordings were made during anesthetic induction with enflurane and enflurane-nitrous oxide in oxygen. The EEG was quantitated using power spectrum analysis. Significant EEG changes were identified during all anesthetic inductions; however, the frequency of occurrence of change was significant only during development of amnesia (15 of 20 subjects, P = 0.04). The nature of the EEG changes at this time was agent-specific (P less than 0.05 by chi-square), with high-frequency changes evident in the enflurane group and shifts in amplitude in the 8-12 Hz activity predominating in the nitrous oxide-enflurane group. Anterior dominance could not be documented as a correlate of amnesia or unresponsiveness. The identification of such EEG changes may be valuable in assessing anesthetic depth, but other effects, such as the response of the EEG to surgical stimulation, must be determined before the results are clinically applicable.