Atmospheric waste isoflurane concentrations using conventional equipment and rat anesthesia protocols

Chronic, low-level exposure of health care professionals to waste anesthetic gases has been linked to increased incidences of neurologic and reproductive dysfunction, hepatic and renal toxicity, and neoplasia. The present study assessed the potential for waste anesthetic gas exposure to researchers administering isoflurane to rats by using standard delivery systems and conventional anesthesia protocols. Well-maintained bench-top precision isoflurane vaporizers were equipped with two circuits (a nonrebreathing one hooked to a modified Bain facemask, and the other to an induction box) attached to commercially available, activated charcoal canisters (passive gas scavenging). The isoflurane concentration was varied from 1% to 5%, while the oxygen flow rate was either 1 or 2.5 L/min. Real-time atmospheric isoflurane levels were assessed by using a portable infrared spectrophotometer. When euthanized female sentinel CD rats were positioned in the facemask loop, isoflurane emissions at the mask rat interface, breathing zone, and exhaust port of scavenging canisters were increased in proportion to the isoflurane concentration and oxygen flow rates as well as the amount of gas directed through the facemask circuit. Isoflurane was detected in the anesthetist s breathing zone only if the entire carrier gas flow was directed to the facemask loop. The background isoflurane level rose to 0.5 ppm after 75 min of continuous bench-top operation in a room with 22 air exchanges hourly but did not escalate if the anesthesia unit--or at least the gas-scavenging canister--was placed in a fume hood, or if the system was used in a room with 42 hourly air changes. Isoflurane efflux via the exhaust ports exceeded 5 ppm in 31% of gas-scavenging canisters that had not reached their maximum use life (as defined by the manufacturer's specifications); in a parallel prospective study, isoflurane was emitted from 88% of canisters by the time that they had reached 50% of their specified lifespan. These data indicate that (1) isoflurane emissions likely will occur at trace levels in laboratory animal facilities even when well-maintained precision isoflurane vaporizers equipped with conventional activated charcoal (passive) gas-scavenging units are used and (2) exposure to anesthetic pollution can be mitigated substantially by selecting low-flow anesthesia regimens, improving gas-scavenging practices, and optimizing the configurations of the delivery system and work area.