Degradation products of sevoflurane during low-flow anaesthesia

Low-flow (1 litre min-1) sevoflurane anaesthesia was used in 16 patients undergoing laparoscopic cholecystectomy (group LSC, n = 8) or tympanoplasty (group TP, n = 8), and concentrations of sevoflurane degradation products were measured. Degradation products in the circuit were measured hourly, and end-tidal carbon dioxide concentration, inspired and end-tidal sevoflurane concentrations, 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 A were 21.6 (SEM 1.6) ppm and 19.6 (0.8) ppm in the LSC and TP groups, respectively (ns). The maximum temperatures of soda lime were 46.4 (0.5) degrees C and 44.8 (0.5) degrees C, respectively (P < 0.05). Hourly end-tidal sevoflurane concentrations and concentrations of sevoflurane degradation products were the same for both groups. Carbon dioxide elimination was the same for both groups 1 h after the start of anaesthesia, but was higher in group LSC after 2 h (P < 0.05). Intraperitoneal carbon dioxide insufflation associated with laparoscopic cholecystectomy had no effect on the concentration of sevoflurane degradation products.