Impact of PEEP Valve Type on Respiratory Effort During Free-Flow Helmet CPAP

Helmet continuous positive airway pressure is widely used to treat acute hypoxemic respiratory failure. However, circuit components such as PEEP valve type may influence airway pressure stability and the work of breathing. We investigated whether V˙-dependent (V˙D) PEEP valves generate additional inspiratory effort compared with V˙-independent (V˙I) PEEP valves and evaluated the potential buffering effect of a reservoir bag.

In this crossover physiological study, 30 healthy volunteers underwent 3 helmet CPAP settings in randomized order: V˙D PEEP valve, V˙I PEEP valve, and V˙-dependent valve combined with a 25-L reservoir bag V˙D-reservoir. Each setting was tested at fresh gas flows of 80 and 120 L/min. Airway pressure swings (ΔP_aw) and nasal pressure swings (ΔP_nose), used as a surrogate of inspiratory effort, were continuously recorded.

V˙D PEEP valves generated significantly larger ΔP_aw compared with V˙I PEEP valves. These airway pressure swings were associated with greater inspiratory effort. Differences in ΔP_nose were evident at 80 L/min, where inspiratory effort was higher with the V˙D PEEP valve, but disappeared at 120 L/min despite persistent differences in ΔP_aw. The addition of a reservoir bag partially attenuated inspiratory effort compared with the V˙D PEEP valve alone.

During helmet CPAP in healthy volunteers, PEEP valve type significantly influenced airway pressure stability and inspiratory effort. V˙I PEEP valves provided more stable airway pressure, whereas V˙D PEEP valves imposed additional inspiratory effort. Increasing fresh gas flow or adding a reservoir bag partially mitigated this effect, highlighting the importance of circuit configuration in optimizing helmet CPAP performance.