The following is a summary of the “A Recirculation System to Reduce the Consumption of Oxygen During CPAP,” published in the February 2023 issue of Respiratory Care by Coppadoro, et al.

A high flow (eg, 60-90 L/min) of gas with F_IO2 titratable up to 1.0 is provided inside a helmet or face mask during continuous flow CPAP for noninvasive respiratory support, and the set pressure is maintained by a PEEP valve. Large quantities of oxygen are lost to leakage while only small amounts are used. Here, they detail an exhaust gas recirculation system intended to reduce oxygen waste. On the bench, a standard Venturi-based continuous flow system was tested while delivering a flow of 60 L/min to a helmet, and a modified system was tested while recirculating oxygen. 

The proposed system captures the oxygen-rich gas that would otherwise escape from the PEEP valve, purges it of carbon dioxide, and then channels it to the helmet via the Venturi flow generator. We compared the regular and recirculation systems by measuring their oxygen consumption, pneumatic performance, and gas conditioning. When compared to a regular system, the recirculation system can cut oxygen consumption by as much as 80%. As F_IO2 and total flow to the helmet went up, oxygen sparing did too. For about 10 hours, a single soda lime canister effectively removed CO₂ from the air. 

When compared to the conventional system, the recirculation system resulted in marginally more severe pressure fluctuations during the breathing cycle (from 3.5–4.4 cm H₂O). Humidity was 6.1 mg/L with the standard setup and 17.3 mg/L with the recirculation system at F₂ 1.0. During a CPAP helmet simulation, oxygen consumption was reduced by 80% thanks to the recirculation system, and CO₂ was removed effectively for more than 10 hours. The CPAP continuous flow system’s pneumatic performance was unaffected by recirculation, and gas conditioning was enhanced in comparison to the standard system.

Source: rc.rcjournal.com/content/68/2/180