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Pharmacodynamic interaction of nitrous oxide with sevoflurane, desflurane, isoflurane and enflurane in surgical patients: measurements by effects on EEG median power frequency

Published online by Cambridge University Press:  16 August 2006

H. Röpcke ,
S. Wirz ,
T. Bouillon ,
J. Bruhn  and
A. Hoeft
H. Röpcke
Affiliation:
Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, D-53123, Germany
S. Wirz
Affiliation:
Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, D-53123, Germany
T. Bouillon
Affiliation:
Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, D-53123, Germany
J. Bruhn
Affiliation:
Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, D-53123, Germany
A. Hoeft
Affiliation:
Department of Anaesthesiology and Intensive Care Medicine, University of Bonn, D-53123, Germany
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Abstract

Background and objective This study investigates the interaction of sevoflurane and nitrous oxide on EEG median power frequency of 2.5 Hz during surgery.

Methods Sevoflurane concentrations required for electroencephalographic median power frequency between 2 and 3 Hz were measured in 25 patients during gynaecological laparotomies. Nitrous oxide was randomly administered at 0, 20, 40, 60 and 75 vol%, subsequently two different concentrations in each patient. The data were analysed using isobolographic analysis together with previously published data on nitrous oxide-isoflurane, -enflurane, or -desflurane interaction.

Results The interaction is described by the equation: C volatile anaesthetic/C0 volatile anaesthetic + C N2O/C0 N2O = 1 (C is the concentrations for a drug combination to achieve the desired effect; C0 is the concentration for single drug use). The parameters are C0 isoflurane = 1.11 vol% (95% CI 1.03–1.19), C0 enflurane = 1.64 (1.52–1.77), C0 desflurane = 5.31 (4.92–5.73), C0 sevoflurane = 2.12 (1.96–2.29), C0 N2O = 174 (153–202). These parameters decrease by 6% (2.5–10) for every 10 years of patients’ age > 40 years.

Conclusions The interaction is compatible with additivity. The potency of nitrous oxide to substitute the volatile anaesthetics is less than anticipated from previously reported MAC values.

Keywords

anaestheticsinhalationdesfluraneisofluranenitrous oxidesevofluranediagnostic techniquesneurologicalelectroencephalographydrug interactionsgynaecological surgical procedureslaparotomymonitoringphysiologicalmonitoringintraoperative
Type
Original Article
Information
European Journal of Anaesthesiology , Volume 18 , Issue 7 , July 2001 , pp. 440 - 449
Copyright
2001 European Society of Anaesthesiology

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