Interference of volatile anaesthetics with infrared analysis of carbon dioxide and nitrous oxide tested in the Dräger Cicero EM using sevoflurane
In theory, setting an infrared multi-gas analyser to measure a volatile anaesthetic different from that in the sampled gas mixture may cause interference with carbon dioxide and nitrous oxide readings. The theory was investigated during evaluation of the Dräger Cicero EM anaesthetic workstation for the Medical Devices Agency. Interference occurred as predicted, and was most pronounced when the vapour analyser of the Cicero EM was deliberately and erroneously set to measure isoflurane, but with sevoflurane present in the gas mixture. With 6% sevoflurane in the gas mixture, the carbon dioxide reading decreased from 5% to 3.6%, and the nitrous oxide reading increased from 0% to 8% although, as the apparent isoflurane reading was 9%, the Cicero EM would alert the operator to the problem. However, operators are encouraged to ensure that, when using gas analysers such as that incorporated into the Cicero EM, the analyser is set to measure the correct volatile anaesthetic (the Cicero EM does this automatically when a Vapor vaporizer is attached) and the breathing system does not contain any other volatile anaesthetic agents.