title: Monitoring of isoflurane and desflurane breakdown: interfering gases and infrared detection.
abstract: OBJECTIVE
  The reaction of isoflurane, enflurane or desflurane with dried CO2 absorbents produces carbon monixide (CO), a highly toxic gas which cannot be detected by gas monitors typically available in the operating room. Trifluoromethane (CHF3) is produced along with CO when this reaction occurs with isoflurane and desflurane, and can be detected by gas monitors. This study will determine the ability of a modified SAM module (Smart Anesthesia Multigas Module, GE/Marquette Medical Systems, Milwaukee, WI) to identify the presence of CHF3, and provide a clinically useful indirect warning of CO production.
  
  
  METHODS
  Isoflurane (1.5%) and desflurane (7.5%) were reacted under clinical conditions with desiccated absorbents resulting in CO production. CO and CHF3 concentrations were measured using gas chromatography. The CHF3 concentrations measured by a modified SAM monitor were compared with the measurements obtained by gas chromatography. Alarm limits set on the SAM monitor were used to warn of the presence of CHF3.
  
  
  RESULTS
  A concentration of 0.25% CHF3, as measured by the SAM monitor, corresponds to an average CO concentration of 780 ppm for isoflurane and 1700 ppm for desflurane. Lowering the threshold to 0.05% CHF3 would result in an average CO concentration of 155 ppm CO for isoflurane and 345 ppm CO for desflurane.
  
  
  CONCLUSIONS
  We have shown that the SAM module is capable of measuring CHF3 due to anesthetic breakdown. With appropriate changes in the display programming and reference cell spectra the monitor would be able to provide an early warning of CO exposure, although the amount of CO would not be reported.
authors.affiliation: Department of Anesthesiology, Froedtert Memorial Lutheran Hospital, 9200 Wisconsin Ave, Milwaukee, WI 53226, USA.
authors.forename: H
authors.initials: H
authors.lastname: Woehlck
authors.forename: M B
authors.initials: MB
authors.lastname: Dunning
authors.forename: K
authors.initials: K
authors.lastname: Nithipatikom
mesh_terms: D000768:Anesthesia, General; D018685:Anesthetics, Inhalation / Q000378:metabolism*; D002138:Calibration; D002248:Carbon Monoxide / Q000032:analysis*; D005617:Chlorofluorocarbons, Methane / Q000032:analysis; D002849:Chromatography, Gas; D000077335:Desflurane; D001330:Electronic Data Processing; D006801:Humans; D007530:Isoflurane / Q000031:analogs & derivatives* / Q000378:metabolism*; D008991:Monitoring, Physiologic; D012680:Sensitivity and Specificity
chemical_list: D018685:Anesthetics, Inhalation; D005617:Chlorofluorocarbons, Methane; D002248:Carbon Monoxide; D000077335:Desflurane; D007530:Isoflurane; C009554:fluoroform