title: Monitoring xenon in the breathing circuit with a thermal conductivity sensor. Comparison with a mass spectrometer and implications on monitoring other gases.
abstract: OBJECTIVE
  To test the accuracy of a thermal conductivity xenon sensor in vitro and in vivo and to test the effect of xenon on other anesthetic gas analyzers as determined by a mass spectrometry gold standard.
  
  
  METHODS
  The xenon concentration was measured with a prototype of a thermal conductivity sensor and a mass spectrometer in vitro and in 6 patients. Further in vitro experiments determined the impact of xenon on the measurements of oxygen, carbon dioxide and desflurane with three commercially available anesthesia gas monitors.
  
  
  RESULTS
  In vitro the thermal conductivity sensor and an associated computer, when calibrated against a mass spectrometer using a third order polynomial calibration curve measured the xenon concentration to a 95% confidence limit of -1.2 to +1.8 vol% compared to mass spectrometry. In vivo and under clinical conditions with a mixture of xenon, O2 and CO2 the 95% confidence limit was -2.5 to +1.6 vol% with a mean bias of -0.5 vol% over a concentration range of 20 to 70 vol%. Xenon induced a clinically relevant bias on the measurements of oxygen (up to 5 vol%), carbon dioxide and desflurane (both twofold overestimation) in a Hewlett-Packard M1025B monitor. In contrast there was only a small bias on the measurements of a Drager PM8060 and a Datex AS3 compact monitor, which was statistically significant (oxygen and desflurane) but clinically irrelevant.
  
  
  CONCLUSIONS
  Thermal conductivity is a clinically useful technique to measure xenon in the breathing circuit despite its statistically significant but clinically irrelevant error compared to mass spectrometry. Other gases of interest have to be measured with selected monitors explicitly approved or tested for use with xenon.
authors.affiliation: Department of Anesthesiology, University Hospital of Bern, Switzerland. martin.luginbuehl@dkf2.unibe.ch
authors.forename: Martin
authors.initials: M
authors.lastname: Luginbühl
authors.forename: Rolf
authors.initials: R
authors.lastname: Lauber
authors.forename: Peter
authors.initials: P
authors.lastname: Feigenwinter
authors.forename: Alex M
authors.initials: AM
authors.lastname: Zbinden
mesh_terms: D000776:Anesthesiology / Q000295:instrumentation*; D018685:Anesthetics, Inhalation / Q000032:analysis; D002245:Carbon Dioxide / Q000032:analysis; D000077335:Desflurane; D006801:Humans; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000032:analysis; D013058:Mass Spectrometry; D010100:Oxygen / Q000032:analysis; D013814:Thermal Conductivity; D014978:Xenon / Q000032:analysis*
chemical_list: D018685:Anesthetics, Inhalation; D002245:Carbon Dioxide; D014978:Xenon; D000077335:Desflurane; D007530:Isoflurane; D010100:Oxygen