Compound A concentration and the temperature of CO₂ absorbents during low-flow sevoflurane anesthesia in surgical patients

Abstract

Sevoflurane, a new inhalational anesthetic, is metabolically broken down into several decomposition products in the presence of CO₂ absorbents. One of the products, CF₂=C (CF₃) OCH₂F (compound A), which appears to be the most toxic, was quantitated in 20 surgical patients subjected to more than 3 h of anesthesia using a low-flow anesthesia circuit. To minimize the variables in the reaction velocity between sevoflurane and the CO₂ absorbents, we maintained the sevoflurane concentration at 2%. Wakolime-A, one type of soda lime, resulted in the highest increase in compound A concentration. The peak concentration was 27.1±3.1 ppm, less than one-tenth of the LC₅₀ (50% lethal concentration) of compound A, which was previously reported as 420 or 400 ppm in rats. We also measured the temperature in CO₂ absorbents, which had been reported to influence compound A production. The elevation in the temperature was 27.9±1.3°C in Wakolime-A, 29.4±8.4°C in Baralyme, and 31.0±5.0°C in Sodasorb II. Further studies are needed to assess the safety and efficacy of sevoflurane.