title: Measurement of anesthetics in blood using a conventional infrared clinical gas analyzer.
abstract: BACKGROUND
  Measurement of the partial pressure of volatile anesthetics in blood is usually done using a "headspace equilibration" method with gas chromatography. However, it is not often performed in clinical studies because of the technical, equipment, and logistic requirements. To improve the accessibility of this measurement, we tested the use of a common infrared clinical gas analyzer, the Datex-Ohmeda Capnomac, for this purpose.
  
  
  METHODS
  After characterization of the linearity of the device in measuring the volatile anesthetic concentration in the presence of nitrous oxide, carbon dioxide, and water vapor, blood was tonometered with known concentrations of sevoflurane (actual value between 0.5% and 5.0%) in oxygen and oxygen/nitrous oxide mixtures, as well as mixtures of isoflurane and desflurane in oxygen.
  
  
  RESULTS
  Mean bias (standard deviation) overall for sevoflurane in oxygen relative to the tonometered reference partial pressure was -4.5 (4.8%) of the actual concentration. This was not altered significantly by measurement in 40% oxygen/60% nitrous oxide. For isoflurane and desflurane it was -3.9 (3.3%) and -4.6 (3.8%), respectively, of the actual concentration.
  
  
  CONCLUSIONS
  The accuracy and precision of measurement of volatile anesthetic gas partial pressures in blood by a double headspace equilibration technique, using a clinical infrared gas analyzer, were comparable to that achieved by previous studies using gas chromatography.
authors: Department of Anaesthesia, Austin Hospital, and University of Melbourne, Melbourne, Australia. phil.peyton@austin.org.au
authors: Philip J
authors: PJ
authors: Peyton
authors: Michael
authors: M
authors: Chong
authors: Christopher
authors: C
authors: Stuart-Andrews
authors: Gavin J B
authors: GJ
authors: Robinson
authors: Robert
authors: R
authors: Pierce
authors: Bruce R
authors: BR
authors: Thompson
mesh_terms: D000769:Anesthesia, Inhalation / Q000295:instrumentation*; D019162:Anesthetics, Combined / Q000097:blood*; D018685:Anesthetics, Inhalation / Q000097:blood*; D002245:Carbon Dioxide / Q000097:blood; D002849:Chromatography, Gas; D000077335:Desflurane; D006801:Humans; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000097:blood*; D008365:Manometry; D008738:Methyl Ethers / Q000097:blood*; D008954:Models, Biological; D009609:Nitrous Oxide / Q000097:blood; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D015203:Reproducibility of Results; D000077149:Sevoflurane; D013055:Spectrophotometry, Infrared / Q000295:instrumentation*; D013997:Time Factors; D014835:Volatilization; D014867:Water / Q000032:analysis
chemical_list: D019162:Anesthetics, Combined; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D014867:Water; D002245:Carbon Dioxide; D000077149:Sevoflurane; D000077335:Desflurane; D007530:Isoflurane; D009609:Nitrous Oxide; D010100:Oxygen