Silica zeolite scavenging of exhaled isoflurane: A preliminary report

Abstract

Purpose: We evaluate the effectiveness of a silica zeolite (Deltazite™) hydrophobic molecular sieve adsorbent, in removing exhaled isoflurane. Methods: In three experiments, a simulated anesthesia mannequin was ventilated using 1% isoflurane in nitrous oxide and oxygen (1:1 ratio) at a gas flow of 3 Lmin-1. Airway pressures, end-tidal carbon dioxide [ETCO2], inspired and end-tidal isoflurane were measured. The scavenging line was connected to a canister containing 750 g of the silica zeolite. Concentrations of isoflurane entering and exiting the canister were measured, as well as the pressure gradient across the canister and gas flow through the canister. In phase 1 (n = 3), the mannequin was ventilated for 6.5 hr, followed by phase 2 where a test lung replaced the simulator. The time (phase 1 plus phase 2) until isoflurane 'breakthrough' (> 0.02%) was noted. Results: The average canister weight increase was 68 g, however 92 g of isoflurane were used. The isoflurane concentration exiting the canister remained undetectable throughout phase 1 in each experiment. The pressure gradient across the canister averaged 0.13 cm H2O and did not increase throughout phase 1. The time to 'break-through' (phase 1 plus phase 2) was 8.0 hr, 8.8 hr and 9.0 hr. Conclusions: Silica zeolite was effective at completely removing 1% isoflurane from exhaled gases for periods of eight hours. The technology shows promise in removing isoflurane emitted from anesthesia machine scavenging systems.