Comparison of the improved oxygenation achieved by three different O₂ flow rates using oxygen delivered by nasal high flow therapy  in patients with acute respiratory failure receiving low, medium or high conventional oxygen therapy.

Oxygen delivered by nasal high flow therapy (HFNO2) is gaining prominence as a therapy for respiratory support in critically ill patients.  In contrast to low flow oxygen devices e.g. the simple face mask or venturi mask, high flow nasal devices are able to deliver flow rates of up to 60 litres/minute. There is less entrainment of room air resulting in an inspired oxygen concentration (FiO₂) delivered that is equal to that set on the device. High flow nasal oxygen is also well tolerated as inspired gas is warmed to 37°C and completely humidified which preserves mucociliary function.  High flow nasal oxygen has been shown to generate of low levels of positive pressure in the upper airways which reduces alveolar collapse and increases lung volume.  Improved efficiency of respiratory effort and decreased work of breathing result from a reduction in respiratory dead space and flushing out of carbon dioxide from the upper airway

The aim of this study is to determine in patients with different severities of respiratory failure, and using HFNO2, the FiO₂ required to maintain low normal oxygen saturations and a respiratory rate that is not excessively high.