Pilot Physiological Evaluation of an Investigational Mask with Expiratory Washout.

The goal of this pilot randomized cross-over study is to compare the effect of a full-face mask with expiratory washout to a conventional full face mask on non-invasive ventilation (NIV) in patients with acute hypercapnic, and acute hypoxemic, respiratory failure. The main questions it aims to answer are: * Does a mask with expiratory washout improve minute ventilation in patients using non-invasive ventilation compared with a conventional single-limb NIV mask * How does a mask with expiratory washout affect respiratory variables compared with a dual-limb NIV mask. Participants already prescribed NIV will undergo 3 arms of the investigation in a randomized order: * Single-limb NIV with investigation mask (with expiratory washout) * Single-limb NIV with conventional mask * Dual-limb NIV with conventional mask

The investigational mask has been designed to deliver non-invasive ventilation (NIV) therapy with expiratory washout. Expiratory washout is a technique designed to flush the upper airway of carbon dioxide at the end of expiration. During conventional NIV the gas at end of exhalation contributes to the functional dead space and "wasted" ventilation. The primary purpose of expiratory washout is to flush the upper airway with fresh gas during exhalation so the next supported breath which drives gas back into the alveolar regions has reduced carbon dioxide. Patients that are admitted to hospital with acute (hypercapnic or hypoxemic) respiratory failure, as assessed by normal hospital protocols, and starting or prescribed to start NIV therapy will be considered for the investigation. Once stabilized on NIV by the physician in charge of their care, eligible patients will be assessed against the inclusion/exclusion criteria and enrolled into the study if applicable. Participants that are enrolled into the study will be put onto oxygen therapy via nasal cannula for 15 minutes, during which time baseline measurements of physiological parameters (such as respiratory rate, tidal volume, minute ventilation and blood gases) and dyspnea scores will be recorded. Following baseline measurements, 32 participants will be randomized into one of the 3 investigational arms and receive NIV with heated humidification according to the randomization protocol for 30 minutes each arm (90 minutes total). The same measurements will be recorded at the end of each 30-minute investigational arm. Participants will cross over to the other 2 conditions consecutively in a random order, each for 30 minutes. The ventilator settings (press support ventilation (PSV), positive end expiratory pressure (PEEP)) will be the following: PSV for tidal volume comprised between 6 and 8 millilitres per kilogram (ml/kg) predicted body weight (PBW), a titration period will be planned at the beginning of the first study period to target a tidal volume of 7 +/-1 ml/kg PBW and the PSV level will be kept constant thereafter. PEEP will be set according to the physician in charge (between 5 and 10 centimetres of water (cmH2O)) if NIV was used before inclusion or will be set by the investigators between 5 and 10 cmH2O. The fraction of inspired oxygen will be titrated manually to target peripheral saturation of oxygen of 88-92% in patients with hypercapnia and 90-94% in patients without hypercapnia. Once the investigation is complete, and participants have successfully finished all 3 arms of NIV therapy, the standard NIV protocols as per local hospital will resume, and participants will return to the care of their usual physician.