Absence of electroencephalographic excitation pattern under isoflurane anesthesia

In twelve patients the EEG was recorded under isoflurane--nitrous oxide inhalation anesthesia. A quiet EEG pattern was registered, without suppressions and seizures of spike activity which are often observed under enflurane. This was the case even when end expiratory CO2 shifted to low values (3-3.6 Vol%). In one patient the induction with N2O/O2 and thiopentone, resulted in spikes and suppression bursts on the EEG. After isoflurane was added, these changes disappeared. In another patient, epileptic EEG patterns were observed prior to the induction (confirmed by the history of the patient). During isoflurane anesthesia the epileptic waves disappeared and remained absent.