Inclusion Criteria:  Adult patients (aged >18 years) presenting in the emergency department De novo acute hypoxemic respiratory failure (requiring oxygen flow rate of 5 liters per minute or more to maintain SpO2 of 90% or more)  Exclusion Criteria:  Age <18 years Not admitted to the hospital Postoperative acute respiratory failure (within one week from surgery) Chronic hypoxemic respiratory failure (requiring long term oxygen therapy at home) Hypercapnic respiratory failure Transferred from another hospital or facility Pregnant women Admitted to the hospital purely to facilitate comfort care Lack of informed consent