Degradation products of sevoflurane during low-flow anaesthesia

Low-flow (1 litre min^–1) sevoflurane anaesthesia was usedin 16 patients undergoing laparoscopic cholecystectomy (groupLSC, n = 8) or tympano-plasty (group TP, n = 8), and concentrationsof sevoflurane degradation products were measured. Degradationproducts in the circuit were measured hourly, and end-tidalcarbon dioxide concentration, inspired and end-tidal sevofluraneconcentrations, and carbon dioxide elimination were monitored.The only degradation product detected was CF₂=C(CF₃)-O-CH₂F(compound A). The mean maximum concentrations of compound Awere 21.6 (SEM 1.6) ppm and 1 9.6 (0.8) ppm in the LSC and TPgroups, respectively (ns). The maximum temperatures of sodalime were 46.4 (0.5) °C, and 44.8 (0.5) °C, respectively(P < 0.05). Hourly end-tidal sevoflurane concentrations andconcentrations of sevoflurane degradation products were thesame for both groups. Carbon dioxide elimination was the samefor both groups 1 h after the start of anaesthesia, but washigher in group LSC after 2 h (P < 0.05). Intraperitonealcarbon dioxide insufflation associated with laparoscopic cholecystectomyhad no effect on the concentration of sevoflurane degradationproducts.