title: Monitoring oxygenator expiratory isoflurane concentrations and the bispectral index to guide isoflurane requirements during cardiopulmonary bypass.
abstract: OBJECTIVE
  The purpose of this study was to measure the changes in isoflurane requirements during the rewarming phase of cardiopulmonary bypass with moderate hypothermia.
  
  
  METHODS
  An observational study.
  
  
  METHODS
  University hospital, single center.
  
  
  METHODS
  Forty patients undergoing elective coronary artery bypass surgery with cardiopulmonary bypass.
  
  
  METHODS
  Isoflurane requirements were quantified by measuring the concentrations in the oxygenator expiratory gas. Anesthesia was guided by bispectral index monitoring.
  
  
  RESULTS
  Isoflurane concentrations required to maintain the bispectral index between 40 and 50 during the rewarming phase of cardiopulmonary bypass were measured. There was a progressive increase in expiratory isoflurane requirements during rewarming from 30 degrees C to 37 degrees C, with a Pearson correlation coefficient of 0.78. There was a significant difference in the concentration required at 30 degrees C (0.41% +/- 0.14%) compared with 37 degrees C (1.00% +/- 0.12%).
  
  
  CONCLUSIONS
  Isoflurane requirements are reduced during hypothermic cardiopulmonary bypass. Monitoring anesthetic concentrations in the oxygenator expiratory gas may be a useful adjunct to monitoring the depth of anesthesia.
authors.affiliation: Department of Anaesthesia, National University Hospital, 5 Lower Kent Ridge Road, 119074 Singapore. analiue@nus.edu.sg
authors.forename: Eugene H C
authors.initials: EH
authors.lastname: Liu
authors.forename: Sasanka S
authors.initials: SS
authors.lastname: Dhara
mesh_terms: D000769:Anesthesia, Inhalation / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000032:analysis*; D001944:Breath Tests; D002315:Cardiopulmonary Bypass / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007530:Isoflurane / Q000008:administration & dosage / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D010107:Oxygenators, Membrane
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane