Canadian Journal of Anesthesia, Vol 46, 192-195, Copyright © 1999 by Canadian Anesthesiologists' Society

ARTICLES

Estimation of desflurane concentration using isoflurane channel in optical infrared analyzer

BC Tsui, DT Jolly and AS Clanachan
Department of Anesthesia, University of Alberta Hospitals, Edmonton, Canada.

PURPOSE: To estimate desflurane concentration on the isoflurane channel in an optical infrared analyzer using a simple regression equation. METHODS: Desflurane in concentrations of 0% to 3% in 0.5% increments and 3% to 12% in 1% increments in 2 L.min-1 oxygen was delivered simultaneously to an Ohmeda 5250 RGM desflurane channel, an Ohmeda 5250 RGM isoflurane channel, and a Datex Capnomac Ultima isoflurane channel at room temperature and atmospheric pressure. For each concentration increment, the displayed gas concentrations were recorded. By comparing the readings from the desflurane channel of Ohmeda RGM and the isoflurane channels from Ohmeda RGM and Datex Capnomac Ultima respectively, the linear regression relationship and the slope of the fitted line (conversion factor) between two channels were obtained. Similar measurements were performed using 2 L.min-1 mixture of nitrous oxide 50% and oxygen 50%. The measurements were repeated with different monitors three months later. RESULTS: All four analysers tested were linear (r2 > 0.9) for measuring desflurane using isoflurane channels over the range of concentrations studied on two different days. The accuracy of the estimation using the mean conversion factor of the four monitors was within 10% error from the readings of the commercially available desflurane channel analyzer. There was no noticeable effect on the slope (conversion factor) of the linear regression with O2 100% or 50/50 mixture of N2O and O2. CONCLUSION: The concentration of desflurane can be estimated by a simple conversion factor using an isoflurane channel of an infrared system.