Adequate hypnosis at very low isoflurane concentration during craniotomy monitored by electroencephalography.

We report a patient with Parkinson's disease undergoing craniotomy for a brain tumor, who had clinically adequate hypnosis at a very low concentration of isoflurane. While the raw EEG showed low-voltage slow electrical activity, the EEG analyzer of the monitor displayed high burst suppression ratios. The role of intracranial pathology and drug therapy as possible causes of the low anesthetic requirement for adequate hypnosis are discussed. This report also draws attention to the possibility of erroneous analysis of burst suppression by EEG modules.