NIV is a life-saving treatment for people with breathing failure and carbon dioxide (CO2) retention. It helps remove this waste gas from the lungs and reduces the effort needed to breathe. However, the standard masks used for NIV can become uncomfortable over time, which may lead patients to stop using them. Stopping treatment can be dangerous and may cause breathing problems to worsen. That's why finding devices that are more comfortable and possibly more effective is very important. This study aims to take a first step in that direction.

This is the first study comparing new devices designed to help people with chronic CO2 buildup during breathing flare-ups. Devices tested include a new type of asymmetrical nasal cannula for high-flow oxygen therapy and a new mask called OptiNIV, which has a comfortable design that may help remove more CO2.

These devices will be compared to standard NIV masks currently used in hospitals. Outcome of interests include their effects on the effort needed to breathe, on how much CO2 is cleared, and on how comfortable they are.

Inclusion Criteria:

• Diagnosed with acute hypercapnic respiratory failure
• Admitted to the intensive care unit
• Being treated with either high-flow oxygen treatment or non-invasive ventilation

Exclusion Criteria:

• Clinical instability - defined as the presence of one of the followings: respiratory rate > 40 breaths/minute, SpO2 < 80%, active broncho-pleural fistula, Glasgow Coma Scale < 8, mean arterial pressure below 60 mmHg despite usage of vasopressors
• Requiring immediate need of endotracheal intubation, according to the judgement of the attending physician
• Contraindications of monitoring with electrical impedance tomography (e.g. pacemaker, chest wall burns wounds limiting electrode placement).

The datasets generated and/or analyzed during the current study are not publicly available due participant confidentiality, according to the REB, but are available from the corresponding author on reasonable request.