• H Röpcke and H Schwilden.
• Klinik und Poliklinik für Anästhesiologie, Rheinischen Friedrich-Wilhelms-Universität Bonn.
• Anaesthesist. 1996 Sep 1; 45 (9): 819-25.

UnlabelledThe aim of this study was to quantify the interaction of enflurane and nitrous oxide at a constant median EEG frequency.MethodsThirty patients were studied during laparotomies. Nitrous oxide was randomly administered in concentrations of 0, 20, 40, 60, and 75 vol.-% for 10 patients for each nitrous oxide concentration. Enflurane vaporizer settings were chosen so that the median EEG frequency was kept constant at 2-3 Hz. The relationship between nitrous oxide concentrations and the required enflurane concentrations was examined with the isobole method.ResultsNitrous oxide decreases the enflurane requirement linearly. Addition of every 10 vol.-% of nitrous oxide decreases the enflurane requirement by 0.042 vol.-%. The total anaesthetic requirement of enflurane and nitrous oxide, expressed in terms of previously reported MAC values, increases significantly with increasing nitrous oxide concentrations.ConclusionsThe interaction of enflurane and nitrous oxide in the dose range from 0 to 75 vol.-% on median EEG frequency is compatible with additivity. The potency of nitrous oxide as a substitute for enflurane is less than might be expected when adding up the MAC values.

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