Sequential Oxygen Therapy Strategy for Patients With COVID-19

All patients with COVID-19 were divided into three groups according to their illness: mild patient who receive conventional oxygen therapy, severe patients who receive nasal high flow oxygen inhalation or non-invasive positive pressure ventilation，all the oxygen therapy will be used as part of the standard of care. Each group will enroll 10 patients, the treatment of all patients will be continuously optimized during observation, and the incidence of respiratory failure, intubation rate, 28 day mortality rate, ICU hospitalization days, etc will be recorded and analyzed so to optimize the treatment time window of sequential oxygen therapy