Comparison of three commercially available activated charcoal canisters for passive scavenging of waste isoflurane during conventional rodent anesthesia.

Chronic, low-level exposure to waste anesthetic gases has been linked to increased incidences of neurologic and reproductive dysfunction, hepatic and renal toxicity, and neoplasia in humans. We have shown previously that one brand of activated charcoal canister (F/Air) used for passive scavenging of halogenated gases does not completely remove isoflurane during anesthetic protocols used in conventional laboratory animal facilities. For the present study, we compared the scavenging capacities of three commercially available canister brands (Breath Fresh, EnviroPure, F/Air) using the same protocol. Well-maintained precision isoflurane vaporizers were equipped with two circuits (a nonrebreathing one hooked to a modified Bain facemask and the other to an induction box), each of which was attached to a canister. Isoflurane concentration and oxygen flow rate were set at 2% and 1 liter/min, respectively. Real-time atmospheric isoflurane emissions from canister exhaust ports were assessed using a portable infrared spectrophotometer. In a random survey of canisters that had not reached their maximal use life (specified by the manufacturers as a weight gain of 50 g), the percentage of canisters emitting > or = 5 ppm but < 100 ppm of waste isoflurane was 46% for Breath Fresh (n = 24), 8% for EnviroPure (n = 39), and 27% for F/Air (n = 37). Failure (defined as an isoflurane efflux of > or = 100 ppm) occurred in 42% of Breath Fresh units but 0% for the other brands. In a subsequent experiment (n = 6/brand), all Breath Fresh and F/Air but no EnviroPure canisters had at least one reading of > or = 5 ppm by the time they gained 30 g. These data indicate that marked variability in gas-scavenging capacity exists between different brands of commercially available activated charcoal canisters and suggest that trace levels of waste isoflurane may occur in high-throughput laboratory animal anesthesia rooms unless canister exhaust also is captured.