Non-Invasive Ventilation Versus High-flow Nasal Oxygen in Intensive Care Units

Inclusion Criteria: * Duration of invasive mechanical ventilation of more than 24h in the ICU before extubation. * Post-extubation respiratory failure occurring within the first 7 days after extubation (see criteria below). As in several previous studies, post-extubation respiratory failure will be defined by the presence of the 2 following criteria combining a clinical criterion and a blood gas criterion: * Clinical criterion persisting for at least 30 minutes: a respiratory rate exceeding 25 breaths per minute or clinical signs of respiratory distress with increased accessory muscle activity. * Blood gas criterion: Hypoxemia defined as PaO2/FiO2 ratio below 150 mm Hg or respiratory acidosis defined as pH below 7.35 units and PaCO2 above 45 mm Hg. For patients under standard oxygen, FiO2 will calculated according to the following formula: FiO2 = 0.21 + 0.03 x (oxygen flow L/min). * Informed consent from the relatives or the patient himself, or emergency inclusion procedure in case of inability of patient or proxy to give consent. Exclusion Criteria: * NIV at home * ICU admission for peripheral neuromuscular disease type Guillain-Barré syndrome or myasthenia gravis. * Upper airway obstruction as main reason for post-extubation respiratory failure * Urgent need for reintubation (respiratory or cardiac arrest, respiratory pauses with loss of consciousness or gasping for air, or severe hypoxemia defined as SpO2 lower than 90% despite maximal oxygen support) * Altered consciousness (Glasgow coma scale \< 12) * Unplanned extubation (accidental or self-extubation) * Do-not-reintubate order at time of respiratory failure * Patient previously included in the study * People under protection (minors, persons deprived of liberty by a judicial or administrative decision, adults under law protection) * Patient not affiliated to health care system.