Influence of the position of charcoal air-filtration canisters on the efficacy of waste isoflurane scavenging as assessed in a randomized experiment.

ABSTRACT

OBJECTIVE To determine whether the position or elevation of charcoal air-filtration canisters would impact efficacy of waste anesthetic gas (WAG) scavenging. DESIGN Randomized experiment. SAMPLE 2 types of bottom-vented and 1 type of top-vented charcoal air-filtration canisters (n = 8 of each canister type/evaluation session). PROCEDURES Canisters were evaluated in a vertical or horizontal position at both low and high isoflurane gas flow rates in a modified Bain nonrebreathing circuit. Waste anesthetic gas concentrations were measured 2.54 cm from canister exhaust ports with an ambient air analyzer every 30 seconds for a maximum of 15 min/experimental condition. One type of bottom-vented canister was tested in a vertical position elevated above or suspended below the vaporizer at a high isoflurane flow rate and then a standard maintenance flow rate. RESULTS Position had no significant effect on WAG emission by any canister type at low isoflurane flow rates. Horizontally positioned bottom-vented canisters at the high isoflurane flow rate emitted significantly more WAG than vertically positioned canisters. Horizontally positioned top-vented canisters at high flow rates emitted significantly more WAG than vertically positioned canisters at the final 15-minute time point only. Cannister types differed significantly in intercanister variability. Canister elevation relative to the vaporizer had no impact on WAG scavenging efficacy. CONCLUSIONS AND CLINICAL RELEVANCE Findings suggested that charcoal air-filtration canisters should be used in a vertical position when anesthetizing animals with the anesthetic delivery system used in this study.