Although many studies have investigated the clinical benefits of nasal high flow during acute hypoxemic respiratory failure, there is no data (and even less so recommendations) on how to best conduct this technique, including its initiation and its weaning periods. Investigators will assess in a multicenter, observational study, the way clinicians use nasal high flow therapy in patients with acute respiratory failure in order to try identify one or more strategies that may be then compared in an interventional study.

Nasal high flow oxygen therapy is increasingly used as a first-line treatment for hypoxemic acute respiratory failure, because of its remarkable tolerance (in comparison with NIV) and its physiological effects (nasopharyngeal dead space washout, positive end-expiratory pressure effect with possible alveolar recruitment, better matching with the patient's inspiratory flow, more reliable and adjustable FiO2); that together contribute to a reduction in respiratory workload and better oxygenation.

Although many studies have investigated the clinical benefits of nasal high flow during acute hypoxemic respiratory failure, there are no data (and even less recommendations) on how to best conduct this technique, including its initiation and its weaning periods.

Because different approaches exist among clinicians, investigators believe that a multicenter observational study that would collect data regarding the different ways high flow is conducted in patients with acute respiratory failure is necessary before performing an interventional study that would test and compare different strategies in order to answer the question: what are the best strategies (in terms of flow and FiO2 settings) to initiate and to wean high-flow oxygen therapy in patients with acute respiratory failure?

Investigators will assess in a multicenter, observational study, the way clinicians use nasal high flow therapy in patients with acute respiratory failure in order to try identify one or more strategies that may be then compared in an interventional study.

Inclusion Criteria:

• Patients aged 18 or older
• admitted to the intensive care unit (ICU) or to the intermediate care for acute hypoxemic respiratory failure (whatever the cause)
• treated with nasal high flow oxygen therapy
• with a minimal FiO2 of FiO2≥50% and a gas flow ≥40 L/min
• anticipated duration of nasal high flow therapy greater or equal to 24 hours

Non-inclusion Criteria:

• prophylactic, post-extubation nasal high flow therapy
• palliative nasal high flow therapy (do-not-resuscitate order)

Exclusion criteria

- nasal high flow therapy administered for less than 24 hours

Adult patients admitted to an ICU or an intermediate care unit, who require nasal high flow oxygen therapy for acute hypoxemic respiratory failure