Inclusion Criteria:  Older than 17 years, admitted to the ICU Confirmed diagnosis of COVID-19 (real-time PCR) Receiving HFNO for at least 4 hours. Patients received HFNO when any of the following criteria were present: peripheral oxygen saturation (SpO2) < 92% with oxygen > 4 liters/minute; increased work of breathing with use of accessory respiratory muscles, and a respiratory rate > 30/min; PaO2/FiO2ratio < 200 mmHg.  Exclusion Criteria:  Patients with respiratory failure secondary to a different etiology, Decreased level of consciousness, Presence of shock requiring vasopressors, Immediate need for intubation. Use of positive-pressure ventilation prior to HFNO, and f) with do-not intubate orders.