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Silica zeolite scavenging of exhaled isoflurane: a preliminary report

[Le captage de l’isoflurane expiré par la zéolithe de silice : un compte-rendu provisoire]

D. John Doyle, MD PhD^*,, Robert Byrick, MD^,, Dusanka Filipovic, PENG and Fred Cashin, RRCP^¶

^* From the University Health Network; Department of Anaesthesia,
University of Toronto; Department of Anaesthesia,
St. Michael’s Hospital; Blue-Zone Technologies Ltd;
and the Patient Simulation Centre,
^¶ St. Michael’s Hospital, Toronto, Ontario, Canada.

Dr Robert J. Byrick, Department of Anesthesia, University of Toronto, Room 132, Fitzgerald Building, 150 College Street, Toronto, Ontario M5S 1A8, Canada. Phone: 416-978-4306; Fax: 416-978-2408; E-mail: robert.byrick{at}utoronto.ca

Purpose: We evaluate the effectiveness of a silica zeolite (Deltazite^TM) 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 L·min^-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 ‘breakthrough’ (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.