Occupational exposure to isoflurane during anaesthesia induction with standard and scavenging double masks in dogs, pigs and ponies.

Induction of anaesthesia using a face mask may cause workplace pollution with anaesthetics. The aim of this study was to compare the effect of the use of a standard versus a scavenging double face mask on isoflurane pollution during induction of anaesthesia in experimental animals: six dogs, 12 pigs and five ponies. Pigs were anaesthetized only once using either mask type randomly (n = 6). Dogs and ponies were anaesthetized twice, using different mask types for each occasion in a random order with at least 14 days between experiments. The masks were attached to a Bain breathing system (dogs and pigs) or to a circle system (ponies) using a fresh gas flow of 300 or 50 mL/kg/min, respectively, with 5% vaporizer dial setting. Isoflurane concentrations were measured in the anaesthetist's breathing zone using an infrared photoacoustic spectrometer. The peak isoflurane concentrations (pollution) during baseline and induction periods were compared with Wilcoxon test in all species, and values between the mask types were compared with either Wilcoxon (ponies and dogs) or Mann-Whitney tests (pigs) (P < 0.05). Pollution was higher during induction when compared with baseline regardless of the mask type used but it was only statistically significant in dogs and pigs. Pollution was lower during induction with double versus single masks but it was only significant in pigs. Despite the lack of statistical significance, large and consistent differences were noted in all species, hence using scavenging masks is recommended to reduce isoflurane workplace pollution.