Compound A concentration is decreased by cooling anaesthetic circuit during low-flow sevoflurane anaesthesia.

Abstract

In the presence of carbon dioxide absorbents, sevoflurane is degraded to CF2 = C(CF3)OCH2F, an olefin compound A. There remains some concern of the hepatic and renal toxicity that compound A poses when using low-flow anaesthetic techniques. We investigated a device to decrease the concentration of compound A products by decreasing the temperature of exhaled air and soda lime in semi-closed low-flow anaesthesia technique in surgical patients. Ten patients, ASA 1 or 2, were studied. Five received anaesthesia using a cooling circuit, that consisting of an anaesthetic circuit and an intercooler device interposed in the expiratory tube. The intercooler was dipped in an iced water tank. Anaesthesia was given through this circuit from induction to emergence. Another five patients received anaesthesia without cooling. Anaesthesia was maintained with sevoflurane and O2 50%/N2O during four to six hours of operation. A fixed concentration of sevoflurane 2% at a total flow of 1 L.min-1 was administered. Gas samples were taken every hour and compound A was quantitated by gas chromatography. The temperatures of canister, circuit and body were measured every hour. The device effectively lowered the temperatures [24 +/- 3.4 to 5 +/- 1.3 degrees C] and the concentrations of compound A [27.1 +/- 3.8 ppm to 16.3 +/- 2.08 ppm, P < 0.05] in the circuit. The body temperatures were not lowered. Compound A concentrations were reduced by cooling the anaesthetic circuit in clinical settings.