Comparison of amsorb®, sodalime, and baralyme® degradation of volatile anesthetics and formation of carbon monoxide and compound A in swine in vivo

Abstract

Background: Consequences of volatile anesthetic degradation by carbon dioxide absorbents that contain strong base include formation of compound A from sevoflurane, formation of carbon monoxide (CO) and CO toxicity from desflurane, enflurane and isoflurane, delayed inhalation induction, and increased anesthetic costs. Amsorb® (Armstrong Ltd., Coleraine, Northern Ireland) is a new absorbent that does not contain strong base and does not form CO or compound A in vitro. This investigation compared Amsorb®, Baralyme® (Chemetron Medical Division, Allied Healthcare Products, St. Louis, MO), and sodalime effects on CO (from desflurane and isoflurane) and compound A formation, carboxyhemoglobin (COHb) concentrations, and anesthetic degradation in a clinically relevant porcine in vivo model. Methods: Pigs were anesthetized with desflurane, isoflurane, or sevoflurane, using fresh or partially dehydrated Amsorb®, Baralyme®, and new and old formulations of sodalime. Anesthetic concentrations in the fresh (preabsorber), inspired (postabsorber), and end-tidal gas were measured, as were inspired CO and compound A concentrations and blood oxyhemoglobin and COHb concentrations. Results: For desflurane and isoflurane, the order of inspired CO and COHb formation was dehydrated Baralyme® > > sodalime > Amsorb®. For desflurane and Baralyme®, peak CO was 9,700 ± 5,100 parts per million (ppm), and the increase in COHb was 37 ± 14%. CO and COHb increases were undetectable with Amsorb®. Oxyhemoglobin desaturation occurred with desflurane and Baralyme® but not Amsorb® or sodalime. The gap between inspired and end-tidal desflurane and isoflurane did not differ between the various dehydrated absorbents. Neither fresh nor dehydrated Amsorb® caused compound A formation from sevoflurane. In contrast, Baralyme® and sodalime caused 20-40 ppm compound A. The gap between inspired find end-tidal sevoflurane did not differ between fresh absorbents, but was Amsorb® < sodalime < Baralyme® with dehydrated absorbents. Conclusion: Amsorb® caused minimal if any CO formation, minimal compound A formation regardless of absorbent hydration, and the least amount of sevoflurane degradation. An absorbent like Amsorb®, which does not contain strong base or cause anesthetic degradation and formation of toxic products, may have benefit with respect to patient safety, inhalation induction, and anesthetic consumption (cost).