Effects of Carbon Dioxide Absorbents on Volatile Anesthetic Degradation Compared in Porcine Model. Kharasch et al. (page 173)

Because some carbon dioxide absorbents used in anesthetic machines contain sodium and potassium hydroxides identified as responsible for anesthetic breakdown and degradant formation, new absorbents with modified amounts or omission of strong bases have been developed. In this study of five to six experiments in 14 pigs, Kharasch et al.  compared the effects of Amsorb®(a new absorbent without a strong base; Armstrong Ltd., Coleraine, Northern Ireland), Baralyme®(Chemetron Medical Division, Allied Healthcare Products, St. Louis, MO), and sodalime, in both fresh and partially dehydrated forms, on carbon monoxide (CO) and compound A formation, carboxyhemoglobin (COHb) concentrations, and anesthetic degradation.

After premedication with ketamine plus xylazine, anesthesia was induced with halothane, and instrumentation for blood sampling was completed. Pigs were randomly assigned to five or six experiments, each lasting 45 min, using anesthesia with sevoflurane, isoflurane, or desflurane, and one of the three absorbents. Baseline samples of breathing circuit gas and arterial blood were obtained before each experiment and at 5, 10, 15, 30, and 45 min after inspiration of sevoflurane, isoflurane, and desflurane to determine hemoglobin, COHb, and oxyhemoglobin amounts in blood and compound A and CO concentrations in gas samples.

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®. Neither fresh nor dehydrated Amsorb®caused compound A formation from sevoflurane, whereas Baralyme®and sodalime caused 20–40 ppm compound A. Its failure to cause formation of toxic products suggests that Amsorb®may benefit patient safety. In addition, the decreases in anesthetic degradation seen in this study may address the issue of anesthetic consumption, thus lowering costs of anesthetics.