Influence of leaks and mask design on CO2 clearance during non-invasive ventilation: a combined bench and physiological study.

Abstract

Background: Non-invasive ventilation (NIV) interface can generate carbon dioxide (CO₂) rebreathing, potentially contributing to NIV failure. The impact of leaks and mask design remains unclear. This study evaluates how these factors influence CO₂ rebreathing in oronasal face masks.

Design, settings, participants: A bench study was followed by a physiological study. The bench study used a mannequin head connected to a breathing simulator exhaling CO₂. Six oronasal face masks designed for single-limb circuits with varying exhalation port positions were tested with three levels of fit. A CO₂ rebreathing index was calculated, along with intentional and unintentional leaks. The best-performing mask was then compared with two clinically used masks in healthy volunteers. Ventilatory ratio (VR, reflecting dead space) was derived from transcutaneous CO₂ (PtcCO₂) and ventilation was assessed by electrical impedance tomography. Analyses used Friedman test and linear mixed-effects model.

Results: The bench study showed (1) mask design as a whole, rather than intentional leak flow rate, was the main determinant of CO₂ rebreathing: exhalation ports situated on the mask body had lower CO₂ rebreathing; (2) unintentional leaks decreased CO₂ rebreathing only with poor mask design and (3) a new under-nose mask with nasal nozzles had the lowest CO₂ rebreathing index. The latter was compared with two other masks in ten volunteers, median aged 32 (IQR 29-34): PtcCO₂ decreased from 37.3 (33.7-39.5) mm Hg at baseline to 32.5 (28.9-35.4) with the new mask (p=0.023). VR with the new mask (0.96 (0.93-1.12)) was lower than with the classical masks (1.40 (1.20-1.50) and 1.38 (1.19-1.45); p<0.001 for both).

Conclusions: Mask design significantly influences CO₂ rebreathing during NIV, with leaks' effects dependent on exhalation port position. A novel under-nose hybrid mask with embedded nozzles reduces CO₂ rebreathing and dead space when compared with classical masks.

Trial registration number: NCT03902639.