title: Effect of nitrous oxide on the bispectral index and the 95% spectral edge frequency of the electroencephalogram during surgery.
abstract: We studied the effect of nitrous oxide on the bispectral index and 95% spectral edge frequency of the electroencephalogram in 20 patients undergoing lumbar surgery under general anaesthesia combined with epidural administration of 5 mg morphine. Anaesthesia was induced with propofol and sufentanil, and maintained with sevoflurane in air/oxygen adjusted to keep the bispectral index between 40 and 60. One and a half hours after the start of surgery, nitrous oxide was administered in a randomised sequence of concentrations (20, 40 and 60% end-expired). Under steady-state conditions, mean (SD) bispectral index and spectral edge frequency decreased as end-tidal concentration of nitrous oxide increased, from 47.7 (4.3) and 15.6 (1.3) at 0% nitrous oxide to 39.8 (6.3) and 14.3 (1.8) at 60% nitrous oxide. A negative correlation was found between nitrous oxide concentration and bispectral index (r = -0.48; p < 0.01) and spectral edge frequency (r = -0.39; p < 0.05). We conclude that this dose-dependent decrease in bispectral index and spectral edge frequency induced by nitrous oxide may reflect the level of analgesia associated with the anaesthetic regimen.
authors.affiliation: University Department of Anaesthesia and Intensive Care Medicine, CHR de la Citadelle, Liege University Hospital, 4000 Liege, Belgium. pol.hans@chu.ulg.ac.be
authors.forename: P
authors.initials: P
authors.lastname: Hans
authors.forename: V
authors.initials: V
authors.lastname: Bonhomme
authors.forename: H
authors.initials: H
authors.lastname: Benmansour
authors.forename: P Y
authors.initials: PY
authors.lastname: Dewandre
authors.forename: J F
authors.initials: JF
authors.lastname: Brichant
authors.forename: M
authors.initials: M
authors.lastname: Lamy
mesh_terms: D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D009609:Nitrous Oxide / Q000494:pharmacology*; D011446:Prospective Studies
chemical_list: D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide