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 inspired gas breathed by patients produced by different types of anesthetic machines under prolonged sevoflurane low-flow anesthesia.

METHODS

The anesthetic machines tested were Excel 210 SE (Datex-Ohmeda, Louisville, CO), Cicero (Dräger, Lübeck, Germany), and AS/3 ADU (Datex-Ohmeda, Louisville, CO). Anesthesia expected to last more than four hours was maintained with 2.0% sevoflurane and nitrous oxide (0.5 L x min(-1))/oxygen (0.5 L x min(-1)). The concentrations of compound A, obtained from the inspiratory limb of the circle system, were measured using a gas chromatograph.

RESULTS

When Excel and Cicero were used, concentrations of compound A increased steadily from the baseline values to 28 and 29 (mean) ppm, respectively, at two hours after exposure to sevoflurane and became constant. There was no significant difference between the concentrations of compound A produced by these anesthetic machines. In contrast, the new anesthetic machine AS/3 was associated with lower concentrations of compound A (6 ppm at one hour, P <0.05 compared with Excel and Cicero), and the concentration did not change significantly thereafter.

CONCLUSION

In spite of the use of a conventional carbon dioxide (CO2) absorbent with strong bases, the anesthetic machine AS/3 with a small volume of canister/soda lime (900 ml/700 ml) produced lower concentrations of compound A than those produced by the other machines.