The Electroencephalogram as a Monitor of Arterial Blood Levels of Methoxyflurane

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Abstract
The electroencephalogram (eeg) was monitored in 40 patients receiving methoxyflurane. Three anesthetic techniques were used depending on the inclusion or omission of thiopental for induction and nitrous oxide during maintenance. Arterial blood levels of methoxyflurane obtained when changes in the eeg occurred were measured by gas chromatography. With increasing depth of anesthesia 4 eeg stages were defined, 3 of which were correlated with blood levels of the agent. These stages showed the classical progession of initial fast activity followed by increasingly slow rhythm, high voltage activity and finally intermittent electrical suppression. Higher levels of methoxyflurane were necessary to produce successive eeg changes where 1st thiopental and then nitrous oxide was omitted from the anesthetic technique. A linear relationship between the level of emthoxyflurane and the eeg stage of anesthesia wes seen.