Exposure to sevoflurane and nitrous oxide during four different methods ofanesthetic induction

The National Institute for Occupational Safety and Health-recommended expos ure levels for nitrous oxide exposure are 25 ppm as a time-weighted average over the time of exposure. The exposure limit for halogenated anesthetics (without concomitant nitrous oxide exposure) is 2 ppm. Inhaled sevoflurane provides an alternative to TV induction of anesthesia. However, the inadver tent release of anesthetic gases into the room is likely to be greater than that with induction involving IV anesthetics. We therefore evaluated anest hesiologist exposure during four different induction techniques. Eighty pat ients were assigned to one of the induction groups to receive: 1) sevoflura ne and nitrous oxide from a rebreathing bag, 2) sevoflurane and nitrous oxi de from a circle circuit, 3) propofol 3 mg/kg, and 4) thiopental sodium 5 m g/kg. Anesthesia was maintained with sevoflurane and nitrous oxide via a la ryngeal mask. Trace concentrations were measured directly from the breathin g zone of the anesthesiologist. During induction, peak concentrations of se voflurane and nitrous oxide with the two IV methods rarely exceeded 2 ppm s evoflurane and 50 ppm nitrous oxide. Concentrations during the two inhalati on methods were generally <20 ppm sevoflurane and 100 ppm nitrous oxide. Du ring maintenance, median values were near 2 ppm sevoflurane and 50 ppm nitr ous oxide in all groups. Sevoflurane concentrations during inhaled inductio n frequently exceeded the National Institute for Occupational Safety and He alth-recommended exposure ceiling of 2 ppm but mostly remained <20 ppm. Exp osure during the maintenance phase of anesthesia also frequently exceeded t he 2-ppm ceiling. We con elude that operating room anesthetic vapor concent rations are increased during inhaled inductions and remain increased with l aryngeal mask ventilation. Implications: We compared waste gas concentratio ns to sevoflurane and nitrous oxide during four different induction methods . During inhaled induction with a rebreathing bag or a circle circuit syste m, waste gas concentrations frequently exceed National Institute for Occupa tional Safety and Health limits of 2 ppm sevoflurane and 50 ppm nitrous oxi de. Therefore, we recommend that people at risk (e.g., women of childbearin g age) should pay great attention when using this technique.