Circuit-dependent carbon dioxide rebreathing during continuous positive airway pressure

The current standard treatment for obstructive sleep apnea (OSA), continuous positive airway pressure (CPAP), is characterized by a low adherence rate due to various factors including circuit-dependent carbon dioxide (CO₂) rebreathing, which can exacerbated by disparate factors, such as low PAP, use of auto-titrating PAP or ramps. However, risk factors for rebreathing are often overlooked or poorly understood in clinical practice. Therefore, our objective was to evaluate the extent of rebreathing occurring with commonly used CPAP masks across varying PAPs, tidal volumes, and respiratory rates.

In a bench study, we assessed the rebreathing rate of nine masks interfacing a CPAP with a lung simulator providing different breathing respiratory rates (15 or 20 breaths/min) and tidal volumes (400, 500, 600, 700 and 750 mL). Additionally, a theoretical model was developed to describe the likelihood of CO₂ rebreathing from four different masks at various breathing settings.

Overall, all masks performed worse in situations characterized by low PAPs, high tidal volumes, and high respiratory rates. However, Dreamwear, Nuance, Siesta, Vitera, and particularly V2 masks exhibited greater susceptibility to rebreathing compared to F20, P10, Brevida, and Rio masks for the same variations of PAPs or ventilatory parameters. The mathematical model suggested that the risk of rebreathing for Rio, P10 and Nuance mask is negligible for respiratory rates of 10 breaths/min or below.

Circuit-dependent CO₂ rebreathing can be a common occurrence and warrants careful mask selection upon CPAP therapy initiation for optimal clinical outcomes.