title: Comparative effects of ketamine on Bispectral Index and spectral entropy of the electroencephalogram under sevoflurane anaesthesia.
abstract: BACKGROUND
  The Bispectral Index (BIS) and spectral entropy of the electroencephalogram can be used to assess the depth of hypnosis. Ketamine is known to increase BIS in anaesthetized patients and may confound that index as a guide to steer administration of hypnotics. We compared the effects of ketamine on BIS, response entropy (RE) and state entropy (SE) during surgery under sevoflurane anaesthesia.
  
  
  METHODS
  Twenty-two women undergoing gynaecological surgery were enrolled in this double-blind, randomized study. Anaesthesia was induced i.v. and maintained with sevoflurane. Under stable surgical and anaesthetic conditions, patients were assigned to receive either a bolus of ketamine 0.5 mg kg(-1) or the same volume of saline. Blood pressure, heart rate, BIS, RE and SE were measured every 2.5 min from 10 min before (baseline) until 15 min after ketamine or saline administration. The maximum relative increase in BIS, RE and SE compared with baseline was calculated for each patient. Values are mean (sd).
  
  
  RESULTS
  Baseline values were BIS 33 (4), RE 31 (5), SE 30 (5) for the ketamine patients and BIS 35 (3), RE 33 (5) and SE 32 (6) for the patients receiving saline. BIS, RE and SE increased significantly from 5 min (BIS) and 2.5 min (RE and SE) after ketamine administration, peaking at 46 (8) (BIS), 52 (12) (RE) and 50 (12) (SE) respectively. The maximum relative increase in RE [42.2 (10.4%)] and SE [41.6 (10.9)%] was higher than that of BIS [29.4 (10.4%)]. Blood pressure, heart rate and RE-SE gradient did not change in either group.
  
  
  CONCLUSIONS
  Ketamine administered under sevoflurane anaesthesia causes a significant increase in BIS, RE and SE without modification of the RE-SE gradient. This increase is paradoxical in that it is associated with a deepening level of hypnosis.
authors.affiliation: CHR Citadelle, University Department of Anaesthesia and Intensive Care Medicine, Liège, Belgium. pol.hans@chu.ulg.ac.be
authors.forename: P
authors.initials: P
authors.lastname: Hans
authors.forename: P-Y
authors.initials: PY
authors.lastname: Dewandre
authors.forename: J F
authors.initials: JF
authors.lastname: Brichant
authors.forename: V
authors.initials: V
authors.lastname: Bonhomme
mesh_terms: D000328:Adult; D019162:Anesthetics, Combined / Q000494:pharmacology; D000778:Anesthetics, Dissociative / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D004311:Double-Blind Method; D004569:Electroencephalography / Q000187:drug effects*; D019277:Entropy; D005260:Female; D013509:Gynecologic Surgical Procedures; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007649:Ketamine / Q000494:pharmacology*; D008738:Methyl Ethers / Q000494:pharmacology*; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D000077149:Sevoflurane; D012815:Signal Processing, Computer-Assisted
chemical_list: D019162:Anesthetics, Combined; D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007649:Ketamine