Rebreathing during CPAP therapy and its implications in obstructive sleep apnea

Elevated environmental carbon dioxide (CO₂) levels can have important health impacts, including increased anxiety, impaired high-level cognitive performance, reduced sleep quality, and decreased next-day alertness, especially in children. Bedrooms, where people spend a third of their lives, are often poorly ventilated, further exacerbating CO₂ exposure during sleep. These symptoms may be of particular concern for individuals with obstructive sleep apnea treated with continuous positive pressure as a result of CO₂ trapping within the mask, which is dependent on environmental levels, and circuit CO₂ rebreathing_. Additionally, lower inhaled oxygen concentrations may be encountered when exhaled gases are rebreathed from the circuit. Low expiratory positive airway pressure, high ventilation levels (eg, in large individuals or at altitude), and small exhaust valves increase rebreathing risk, which can self-propagate due to patient attempts to compensate by increasing tidal volume. Elevated environmental CO₂ may further exacerbate the clinical consequences of rebreathing, including reduced continuous positive pressure adherence. Although strategies including higher expiratory positive airway pressure or larger exhaust valves help mitigate CO₂ buildup, they can also lead to increased noise, which may potentially affect adherence. With this work, we review the available evidence on the thresholds and effects of classroom, office, bedroom, and rebreathed CO₂ levels in healthy individuals and those with obstructive sleep apnea, both adults and children. Importantly, we provide the often-overlooked link between environmental CO₂ concentrations and circuit rebreathing for patients with obstructive sleep apnea, underscoring the need to optimize current indoor ventilation standards and thresholds for mask-based CO₂ inhalation, as well as continuous positive pressure technology to maximize adherence, abate CO₂/hypoxic exposure, and improve health outcomes.

Noah WH, White DP, Hete B, Messineo L. Rebreathing during CPAP therapy and its implications in obstructive sleep apnea. J Clin Sleep Med. 2025;21(10):1759-1771.