Production of compound A under low-flow anesthesia is affected by type of anesthetic machine

Purpose: The purpose was to compare the concentrations of compound A in ins pired gas breathed by patients produced by different types of anesthetic ma chines under prolonged sevoflurane low-flow anesthesia. Methods: The anesthetic machines tested were Excel (TM) 210 SE (Datex-Ohmed a, Louisville, CO), Cicero (TM) (Drager, Lubeck, Germany), and AS/3 (TM) AD U (Datex-Ohmeda, Louisville, CO). Anesthesia expected to last more than fou r hours was maintained with 2.0% sevoflurane and nitrous oxide (0.5 L(.)min (-1)) / oxygen (0.5 L(.)min(-1)). The concentrations of compound A, obtaine d from the inspiratory limb of the circle system, were measured using a gas chromatograph. Results: When Excel (TM) and Cicero (TM) were used, concentrations of compo und A increased steadily from the baseline values to 28 and 29 (mean) ppm, respectively, at two hours after exposure to sevoflurane and became constan t. There was no significant difference between the concentrations of compou nd A produced by these anesthetic machines. In contrast, the new anesthetic machine AS/3 (TM) was associated with lower concentrations of compound A ( 6 ppm at one hour. P <0.05 compared with Excel (TM) and Cicero (TM)), and t he concentration did not change significantly thereafter. Conclusion: In spite of the use of a conventional carbon dioxide (CO2) abso rbent with strong bases. the anesthetic machine AS/3 (TM) with a small volu me of canister/soda lime (900 ml/700 ml) produced lower concentrations of c ompound A than those produced by the other machines.