1. COVID-19 (positive RT-PCR test and interstitial pneumonia observed in CT scan), 2. Clinically severe interstitial pneumonia with respiratory failure / pre ARDS (MEWS classification of 3-4 points), 3. <90-92% SpO2 at rest 4. Consent to participate in the study.

1. COVID-19 (positive RT-PCR test and interstitial pneumonia observed in CT scan), 2. Clinically severe interstitial pneumonia with respiratory failure / pre ARDS (MEWS classification of 3-4 points), 3. <90-92% SpO2 at rest 4. Consent to participate in the study.