Sequential Oxygen Therapy Strategy for Patients With COVID-19

Inclusion Criteria: * Patients diagnosed with COVID-19 * Aged between 18-75 years; * Willing to sign the informed consent voluntarily. Exclusion Criteria: * Patients with active tuberculosis, idiopathic pulmonary fibrosis, bronchial asthma, bronchiectasis, pulmonary embolism, chronic respiratory failure or other serious respiratory diseases; ② patients with serious cardiovascular and cerebrovascular diseases (malignant arrhythmia, unstable angina, acute myocardial infarction, cardiac function grade 3 or above, stroke, cerebral hemorrhage, etc.); ③ Patients with serious hepatorenal diseases (serious liver diseases refer to cirrhosis, portal hypertension and varicose bleeding, and serious kidney diseases include dialysis and kidney transplantation); ④ tumor patients who have undergone resection, radiotherapy and chemotherapy within 5 years; ⑤ patients who have difficulty in activity due to neuromuscular diseases; ⑥ patients with serious arthritis; ⑦ patients with serious peripheral vascular diseases; ⑧ Pregnant and lactating women; ⑨ with severe cognitive and mental disorders; ⑩ the clinical researchers who were participating in other interventions within one month before selection;