First-line therapy of patients with acute respiratory failure consists in oxygen delivery through standard oxygen, high-flow nasal oxygen therapy through cannula or non-invasive ventilation. Non-invasive ventilation in acute hypoxemic respiratory failure is not recommended. In a large randomized controlled study, high-flow nasal oxygen has been described as superior to non-invasive ventilation and standard oxygen in terms of mortality but not of intubation. Paradoxically in immunocompromised patients, high-flow nasal oxygen has not been shown to be superior to standard oxygen. To improve the level of evidence of daily clinical practice, we propose comparing high-flow nasal oxygen versus standard oxygen, in terms of mortality in all patients with acute hypoxemic respiratory failure

Inclusion Criteria:

All consecutive patients older than 18 years with an acute hypoxemic respiratory failure will be enrolled if they meet all the following criteria:

• Respiratory rate >25 breaths/min whatever the oxygen support
• Pulmonary infiltrate,
• PaO2/FiO2 ≤200 mmHg
• Informed consent from the patient or relatives.

Exclusion Criteria:

• PaCO2 > 45 mm Hg
• Need for emergent intubation: pulse oximetry < 90% with maximum oxygen support, respiratory arrest, cardiac arrest, or Glasgow coma scale below 8 points
• Hemodynamic instability defined by signs of hypoperfusion or use of vasopressors > 0.3 µg/kg/min
• Glasgow coma scale equal to or below 12 points
• Exacerbation of chronic lung disease including chronic obstructive pulmonary disease (grade 3 or 4 of Gold classification), or another chronic lung disease with long term oxygen or ventilatory support
• Cardiogenic pulmonary edema as main reason for acute respiratory failure
• Coronavirus SARS-2 infection as reason for acute respiratory failure (the SOHO-COVID study has been completed)
• Post-extubation respiratory failure within 7 days after extubation,
• Post-operative patients within 7 days after abdominal or cardiothoracic surgery,
• Do not intubate order;
• Already included in the study, refusal to participate or participation in another interventional study with the same primary outcome.
• Patients without any healthcare insurance scheme or not benefiting from it through a third party,
• Persons under law protection, namely minors, pregnant or breastfeeding women, persons deprived of their liberty by a judicial or administrative decision.

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