Comparison Between High-flow Nasal Cannula System and Non-invasive Ventilation in Acute Hypoxemic Respiratory Failure

Inclusion Criteria: * Age above 18 * patients with acute hypoxemic respiratory failure Exclusion Criteria: * age \< 18 years * hypercapnia (arterial carbon dioxide tension (PaCO2) \>45mmHg) at admission * need for emergency intubation, including cardiopulmonary resuscitation * recent esophageal, facial or cranial trauma or surgery * severely decreased consciousness (Glasgow coma score \<11) * cardiogenic shock or severe hemodynamic instability * systolic blood pressure \<90 mmHg associated with decreased urinary output(\<20 mL.h-1) despite fluid repletion and use of vasoactive agents * lack of co-operation * altered mental status with decreased consciousness and/or evidence of inability to understand or lack of willingness to co-operate with the procedures * tracheotomy or other upper airway disorders * severe ventricular arrhythmia or active myocardial ischemia * active upper gastrointestinal bleeding * inability to clear respiratory secretions * more than one severe organ dysfunction in addition to respiratory failure