A Recirculation System to Reduce the Consumption of Oxygen During CPAP

During continuous flow CPAP for noninvasive respiratory support, a high flow (eg, 60-90 L/min) of gas with F_IO titratable up to 1.0 is provided 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.

A 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.

The recirculation system reduced the oxygen consumption up to 80% as compared to the standard system. Oxygen sparing increased with increasing F_IO 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 F_IO 1.0, humidity was 6.1 mg/L and 17.3 mg/L with the standard and the recirculation system, respectively.

The recirculation system allowed a 80% 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.