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TECHNOLOGY, COMPUTING, AND SIMULATION

Carbon Monoxide Production from Sevoflurane Breakdown: Modeling of Exposures Under Clinical Conditions

Elena J. Holak, MD PharmD^*, David A. Mei, MD PhD^*, Marshall B. Dunning, III, PhD, Rao Gundamraj, MD^*, Randa Noseir, MD^*, Lu Zhang, MD PhD^*, and Harvey J. Woehlck, MD^*

Department of *Anesthesiology and Pulmonary and Critical Care Medicine, Medical College of Wisconsin, Milwaukee

Address correspondence and reprint requests to Harvey Woehlck, MD, Department of Anesthesiology, Froedtert Memorial Lutheran Hospital West, 9200 W. Wisconsin Ave., Milwaukee, WI 53226. Address e-mail to hwoehlck{at}mcw.edu

Isoflurane, enflurane, sevoflurane, and especially desflurane produce carbon monoxide (CO) during reaction with desiccated absorbents. Of these, sevoflurane is the least studied. We investigated the dependence of CO production from sevoflurane on absorbent temperature, minute ventilation (VE), and fresh gas flow rates. We measured absorbent temperature and in vitro CO concentrations when desiccated Baralyme reacted with 1 minimum alveolar anesthetic concentration of (2.1%) sevoflurane at 2.3-, 5.0-, and 10.0-L VE. Mathematical modeling of carboxyhemoglobin concentrations was performed using an existing iterative method. Rapid breakdown of sevoflurane prevented the attainment of 1 minimum alveolar anesthetic concentration with low fresh gas flow rates. CO concentrations increased with VE and with absorbent temperatures exceeding 80°C, but concentrations decreased with higher fresh gas flow rates. Average CO concentrations were 150 and 600 ppm at 2.3- and 5.0-L VE; however, at 10 L, over 11,000 ppm of CO were produced followed by an explosion and fire. Methanol and formaldehyde were present and may have contributed to the flammable mixture but were not quantitated. Mathematical modeling of exposures indicates that in average cases, only patients 25 kg, or severely anemic patients, are at risk of carboxyhemoglobin concentrations >10% during the first 60 min of anesthesia.

IMPLICATIONS: Sevoflurane breakdown in desiccated absorbents is expected to result in only mild carbon monoxide (CO) exposure. Completely dry absorbent and high minute ventilation rates may degrade sevoflurane to extremely large CO concentrations. Serious CO poisoning or spontaneous ignition of flammable gases within the breathing circuit are possible in extreme circumstances.

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