Monitoring of isoflurane and desflurane breakdown: Interfering gases and infrared detection

Objective. The reaction of isoflurane, enflurane or desflurane with dried C O2 absorbents produces carbon monixide (CO), a highly toxic gas which canno t be detected by gas monitors typically available in the operating room. Tr ifluoromethane (CHF3) is produced along with CO when this reaction occurs w ith isoflurane and desflurane, and can be detected by gas monitors. This st udy will determine the ability of a modified SAM module (Smart Anesthesia M ulti-gas Module, GE/Marquette Medical Systems, Milwaukee, WI) to identify t he presence of CHF3, and provide a clinically useful indirect warning of CO production. Methods.Isoflurane (1.5%) and desflurane (7.5%) were reacted u nder clinical conditions with desiccated absorbents resulting in CO product ion. 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 SA M monitor were used to warn of the presence of CHF3. Results. A concentrati on 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. Lo wering the threshold to 0.05% CHF3 would result in an average CO concentrat ion 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 ane sthetic breakdown. With appropriate changes in the display programming and reference cell spectra the monitor would be able to provide an early warnin g of CO exposure, although the amount of CO would not be reported.