Low-flow anesthesia and reduced animal size increase carboxyhemoglobin levels in swine during desflurane and isoflurane breakdown in dried soda lime

After institutional approval, we studied the effect of animal size, anesthe tic concentration, and fresh gas flow (FGF) rate on inspired carbon monoxid e (CO) and carboxyhemoglobin (COHb) during anesthesia in swine, using soda Lime previously dried to 1 +/- 0.1% water content. To ascertain the effect of anesthesia, eight adult pigs were anesthetized with either 1 minimum alv eolar anesthetic concentration (MAC) desflurane or isoflurane and, to chara cterize the effect of the FGF rate, it was doubled in four pigs. To determi ne the effect of animal size, four small and four large pigs received 1 MAC desflurane or isoflurane, and to determine the effect of the anesthetic co ncentration, a group of four swine was exposed to 0.5 MAC. CO and COHb conc entrations were larger with desflurane (5500 +/- 980 ppm and 57.90% +/- 0.5 0%, respectively) than with isoflurane (800 ppm and 17.8% +/- 2.14%, respec tively), especially in the small animals. Increasing the FGF rate significa ntly reduced peak CO and COHb concentrations resulting from both anesthetic s; however, when each anesthetic was reduced to 0.5 MAC, the concentrations obtained were similar. We conclude that CO intoxication is more severe wit h desflurane than with isoflurane, that small animals are at higher risk fo r CO poisoning, and that low FGF can increase COHb concentrations. Implicat ions: The present study shows that the use of desflurane with desiccated ca rbon dioxide absorbents in pediatric anesthesia can produce a dangerous car bon dioxide intoxication, especially with low-flow anesthesia.