Inclusion Criteria:  PCR (+) P/F ≤300 mmHg (despite standard mask oxygen support from 15 L/min for 15 minutes) Respiratory rate ≥24/min or signs of respiratory failure (intercostal retraction, nasal wing breathing)  Exclusion Criteria:  Chronic respiratory failure Cardiogenic pulmonary edema Aplasia GCS ≤12 Hemodynamic instability (use of vasopressors) Emergency intubation requirement