title: Surgical stimulation shifts EEG concentration-response relationship of desflurane.
abstract: BACKGROUND
  Anesthesiologists routinely increase the delivered anesthetic concentration before surgical stimulation in anticipation of increased anesthetic requirement to achieve certain goals (e.g., amnesia, unconsciousness, and immobility). Electroencephalographic monitoring is one method of determining indirectly anesthetic effect on the brain. The present study investigated the effect of surgical stimuli on the concentration-response relation of desflurane-induced electroencephalographic changes.
  
  
  METHODS
  The electroencephalographic activity was recorded from 24 female patients who received only desflurane after a single induction dose of propofol. Twelve patients served as a control group before surgical stimulation. The other 12 patients, all undergoing lower abdominal surgery, were investigated between opening and closure of the peritoneum. Desflurane vaporizer settings were randomly increased and decreased between 0.5 and 1.6 minimum alveolar concentration as long as anesthesia was considered adequate. Spectral edge frequency 95, median power frequency, and Bispectral Index were calculated. Desflurane effect-site concentrations and the concentration-effect curves for spectral edge frequency 95, median power frequency, and Bispectral Index were determined by simultaneous pharmacokinetic and pharmacodynamic modeling.
  
  
  RESULTS
  Surgical stimulation shifted the desflurane concentration-electroencephalographic effect curves for spectral edge frequency 95, median power frequency, and Bispectral Index toward higher desflurane concentrations. In the unstimulated group, 2.2 +/- 0.74 vol% desflurane were necessary to achieve a Bispectral Index of 50, whereas during surgery, 6.8 +/- 0.98 vol% (mean +/- SE) were required.
  
  
  CONCLUSIONS
  During surgery, higher concentrations of the volatile anesthetic are required to achieve a desired level of cortical electrical activity and, presumably, anesthesia.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Germany. roepcke@mailer.meb.uni.bonn.de
authors.forename: H
authors.initials: H
authors.lastname: Röpcke
authors.forename: B
authors.initials: B
authors.lastname: Rehberg
authors.forename: M
authors.initials: M
authors.lastname: Koenen-Bergmann
authors.forename: T
authors.initials: T
authors.lastname: Bouillon
authors.forename: J
authors.initials: J
authors.lastname: Bruhn
authors.forename: A
authors.initials: A
authors.lastname: Hoeft
mesh_terms: D000005:Abdomen / Q000601:surgery; D000328:Adult; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics / Q000494:pharmacology*; D016022:Case-Control Studies; D000077335:Desflurane; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D018685:Anesthetics, Inhalation; D000077335:Desflurane; D007530:Isoflurane