Respiratory failure is the most frequent organ failure and cause for admission in the Intensive Care Unit (ICU) . It is a severe complication with an ICU mortality ranged from 31% to 33%. Symptomatic treatment of hypoxemic respiratory failure is a controversial topic with different options: 1) standard oxygen therapy, 2) high flow nasal cannula oxygen therapy (HFNC) and 3) non-invasive ventilation (NIV).

The aim of the study is to compare HFNC versus NIV ventilation using CT scan. The hypothesis of this study is that in hypoxemic critically ill patients, the increase of lung volumes with NIV would be significantly higher than the increase of lung volumes with HFNC.

Inclusion Criteria:

• Patient with hypoxemia at any time of ICU stay defined as follow: standard oxygen therapy flow ≥ 3L/min to maintain a pulsed oxygen saturation ≥ 95%
• Adult (age ≥ 18 years)
• (2) A CT scan prescribed by the physician in charge of the patient as part of the exploration of the patient's pathology and not as part of a "dedicated" prescription for the study.

Exclusion Criteria:

• NIV contraindication (need for immediate endotracheal intubation and mechanical ventilation; hemodynamic instability defined by systolic blood pressure < 90 mmHg or mean blood pressure < 65 mmHg, use of vasopressors; Glasgow Coma Scale score of 12 points or less)
• History of recent facial trauma not compatible with the use of nasal cannulas
• Pregnancy
• Refusal of study participation
• protected person
• Patient not affiliated to the social security system or not benefiting from such a system
• Lack of signed informed consent

12 months after the main publication

Data are provided to qualified investigators free of charge. Required documents to request data include a summary of the research plan, request form, and institutional review board (IRB) review. Dataset will be shared after careful examination by the study board of investigators.