title: The bispectral index predicts responsiveness to verbal commands in patients emerging from nitrous oxide anesthesia supplemented with a subhypnotic concentration of isoflurane.
abstract: OBJECTIVE
  Nitrous oxide (N2O) administered alone has minimal effects on the bispectral index (BIS), an electroencephalogram-derived parameter of hypnosis. However, because this gas is commonly supplemented with a volatile anesthetic, we sought to determine how it would affect the BIS when coadministered with a low concentration of isoflurane.
  
  
  METHODS
  Twelve patients were anesthetized with 70% N2O + 0.2% isoflurane (all concentrations are end-tidal). Following the end of surgery, the concentration of N2O was decreased in decrements of 10% while isoflurane was continued at 0.2%, and each new concentration of N2O was maintained for 15 min. This procedure was repeated until the patients first opened their eyes or squeezed the investigator's hand on command.
  
  
  RESULTS
  N2O 70% + isoflurane 0.2% reduced the BIS to 68 +/- 9 (mean +/- SD). When the concentration of N2O was decreased toward awakening (which occurred at the N2O concentration of 36% +/- 8%), the BIS progressively increased until it reached 93 +/- 5 on awakening.
  
  
  CONCLUSIONS
  The BIS reflects the level of hypnosis during N2O anesthesia supplemented with a low concentration of isoflurane.
authors.affiliation: Department of Anesthesia and Critical Care, Teikyo University School of Medicine, 2-11-1 Kaga, Itabashi-ku, Tokyo 173-8605, Japan.
authors.forename: Takahisa
authors.initials: T
authors.lastname: Goto
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ishiguro
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Nakata
authors.forename: Shigeho
authors.initials: S
authors.lastname: Morita
mesh_terms: D000328:Adult; D000769:Anesthesia, Inhalation; D004569:Electroencephalography; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage*; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage*
chemical_list: D007530:Isoflurane; D009609:Nitrous Oxide