Non-invasive CPAP with face mask: comparison between different devices

Introduction

This study compared the reliability and the efficacy of three different non-invasive CPAP systems, Ventumask^® low flow (LF), Ventumask^® high flow (HF) and Boussignac^® CPAP valve (B), both in a lung model and in healthy subjects.

Methods

Lung model: pneumatic simulator first set at respiratory rate 16/minute with 400 ml tidal volume (L1), then RR 40/minute with 800 ml tidal volume (L2). Human study: 10 healthy subjects were asked to make an expiratory pause (T1), five breaths at tidal volume (T2), and a short sequence of tachypnea (T3). The differences between set and effective PEEP and FiO₂ were used as indexes of reliability. The minimum airway pressure below the PEEP level and the airway pressure swing around PEEP were used as indexes of efficacy. In the lung simulator protocol, the pressure-time product was measured and then correlated to the other efficacy indexes.

Results

Lung model: HF showed a tendency towards a more stable PEEP (P = 0.067). In B a significant fall in the FiO₂ value from L1 (96.9 (95.5; 97.6)%) to L2 (54.2 (50.4; 56.9)%) was observed (P < 0.001). The airway pressure swing around PEEP was greater in LF and B compared with HF in L1 (P < 0.001), while during L2 it was lower in B (P = 0.007). The pressure-time product was better described by the airway pressure swing around PEEP (r² = 0.95) rather than the minimum airway pressure below the PEEP level (r² = 0.85). Human study: a lower difference between set and effective FiO₂ was registered with HF (P < 0.001). Ventumask^® systems showed an overall higher minimum airway pressure below the PEEP level compared with B (P < 0.001). During T3, HF (+10.1 (+7.4; +13.2) cmH₂O) showed a smaller airway pressure swing around PEEP relative to LF (+11.9 (+10.1; +16.6) cmH₂O, P < 0.001) but not to B (+12.2 (+6.6; +15.1) cmH₂O, P = 0.40). During the whole respiratory sequence, an increase in end-expiratory pressure was observed. This increase was greater in B valve than in HF and LF (P < 0.001).

Conclusions

According to observations, HF seemed to be the most reliable device. In conditions of high flow demand, B reached FiO₂ values lower than expected. The dynamic hyper-pressurization, higher with B, is probably due to the relationship between expiratory flow and the resistance offered by the expiratory valve. B, even if handy and lightweight, is less reliable in terms of flow supply and PEEP stability.