• Andrea Coppadoro, Luca Paratico, and Giacomo Bellani.
• Department of Anesthesia and Intensive Care, San Gerardo Hospital, ASST Monza, Monza, Italy.
• Respir Care. 2022 Nov 22; 68 (2): 180187180-7.

BackgroundDuring continuous flow CPAP for noninvasive respiratory support, a high flow (eg, 60-90 L/min) of gas with FIO2 titratable up to 1.0 is flown within a helmet or face mask, while a PEEP valve maintains the set pressure. A large amount of oxygen is wasted, whereas only a minimal amount is consumed. We describe a recirculation circuit designed to reuse the exhaust gas and save oxygen.MethodsA standard Venturi-based continuous flow system delivering a flow of ≥ 60 L/min to a helmet, and a modified system designed to recirculate oxygen were tested on the bench during simulated active breathing. The proposed system recirculates the oxygen-enriched gas escaping from the PEEP valve; after CO2 removal, the gas is entrained by the Venturi flow generator and redirected to the helmet. We compared oxygen consumption, pneumatic performance, and gas conditioning of the standard and the recirculation systems.ResultsThe recirculation system reduced the oxygen consumption up to 80% as compared to the standard system. Oxygen sparing increased with increasing FIO2 and total flow delivered to the helmet. Exhaled CO2 was efficiently removed by a single soda lime canister for about 10 h. Pressure swings during a respiratory cycle slightly worsened when using the recirculation system as compared to the standard one (from 3.5-4.4 cm H2O). At FIO2 1.0, humidity was 6.1 mg/L and 17.3 mg/L with the standard and the recirculation system, respectively.ConclusionsThe recirculation system allowed a 4/5-fold reduction of oxygen consumption during simulated helmet CPAP therapy, whereas CO2 removal was effective for > 10 h. Recirculation minimally affected pneumatic performance of the CPAP continuous flow system, while improving gas conditioning as compared to the standard system.Copyright © 2022 by Daedalus Enterprises.

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