title: Changes of electroencephalographic bicoherence during isoflurane anesthesia combined with epidural anesthesia.
abstract: BACKGROUND
  The authors previously reported that, during isoflurane anesthesia, electroencephalographic bicoherence values changed in a fairly restricted region of frequency versus frequency space. The aim of the current study was to clarify the relation between electroencephalographic bicoherence and the isoflurane concentration.
  
  
  METHODS
  Thirty elective abdominal surgery patients (male and female, aged 34-77 yr, American Society of Anesthesiologists physical status I-II) were enrolled. After electroencephalogram recording with patients in an awake state, anesthesia was induced with 3 mg/kg thiopental and maintained with oxygen and isoflurane. Continuous epidural anesthesia with 80-100 mg/kg 1% lidocaine was also administered. Using software they developed, the authors continuously recorded the FP1-A1 lead of the electroencephalographic signal and expired isoflurane concentration to an IBM-PC compatible computer. After confirming the steady state of each isoflurane (end-tidal concentration at 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, and 1.5%), electroencephalographic bicoherence values were calculated.
  
  
  RESULTS
  In a light anesthetic state, electroencephalographic bicoherence values were low (generally < or = 15.0%). At increased concentrations of isoflurane, two peaks of electroencephalographic bicoherence emerged along the diagonal line (f1=f2). The peak emerged at around 4.0 Hz and grew higher as isoflurane concentration increased until it reached a plateau (43.8 +/- 3.5%, mean +/- SD) at isoflurane 0.9%. The other peak, at about 10.0 Hz, also became significantly higher and reached a plateau (32.6 +/- 9.2%) at isoflurane 0.9%; at isoflurane 1.3%, however, this peak slightly decreased.
  
  
  CONCLUSIONS
  Changes in the height of two electroencephalographic bicoherence peaks correlated well with isoflurane concentration.
authors.affiliation: Department of Anesthesiology, Osaka Prefectural Habikino Hospital, 3-7-1 Habikino, Habikino City, Osaka, Japan 583-8588. hagihira@masui.med.osaka-u.ac.jp
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hagihira
authors.forename: Masaki
authors.initials: M
authors.lastname: Takashina
authors.forename: Takahiko
authors.initials: T
authors.lastname: Mori
authors.forename: Takashi
authors.initials: T
authors.lastname: Mashimo
authors.forename: Ikuto
authors.initials: I
authors.lastname: Yoshiya
mesh_terms: D000328:Adult; D000368:Aged; D000767:Anesthesia, Epidural; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane