High Flow Nasal Oxygen for Acute Hypoxemic Respiratory Failure in the Emergency Room

Inclusion Criteria: * Age ≥ 18 years; * PaO2/FiO2 ratio between 250 and 150 mmHg or SpO2/FiO2 ratio between 190 and 274, after at least 15 minutes of spontaneous breathing through a Venturi mask (VM), with a FiO2 targeted at a SpO2 94-97%; * Respiratory rate(RR)≤35breaths/min,afteratleast15minutesofspontaneous breathing through a VM, with a FiO2 targeted at a SpO2 94-97%; * PaCO2 ≤ 45 mmHg; * Unilateral or bilateral infiltrate(s), as detected with chest radiography and/or computed tomography and/or with lung ultrasound not fully explained by effusions, atelectasis, or nodules/masses. Infiltrates at lung ultrasound are defined as presence of focal B-lines, consolidations (with irregular marginal contour, air bronchogram, air trapping sign) and irregularity of the pleural line. Exclusion Criteria: * Respiratory failure due to: * Acute asthma or COPD exacerbation, * Cardiac failure or fluid overload as primary cause of respiratory failure; * Unstable angina or ongoing acute myocardial infarction; * Acute respiratory acidosis with pH \< 7.35 and PaCO2 \> 45 mmHg; * Hemodynamic instability and/or use of vasopressors/inotropes; * Altered mental status (Kelly \>3), see Figure 1;(18) * Contraindications to NIV (high risk of aspiration pneumonia, impaired airways protection, head-facial trauma and/or burns, uncooperative patient, cranial/thoracic/abdominal open wounds); * Indications to urgent intubation performed according to the clinician in charge; * Body Mass Index \> 35 kg/m2; * Pregnancy; * Patient's refusal to participate.