inclusion criteria: age: 18-80 years old, male and female; covid-19 confirmed cases; comply with any of the following: dyspnea, rr ≥ 30 times / min; in resting state, transcutaneous oxygen saturation ≤ 93%; oxygenation index (pao2 / fio2) < 300mmhg; pulmonary imaging showed diffuse exudative lesions.

inclusion criteria: age: 18-80 years old, male and female; covid-19 confirmed cases; comply with any of the following: dyspnea, rr ≥ 30 times / min; in resting state, transcutaneous oxygen saturation ≤ 93%; oxygenation index (pao2 / fio2) < 300mmhg; pulmonary imaging showed diffuse exudative lesions.

inclusion criteria: 1. age: 18-80 years old, male and female; 2. covid-19 confirmed cases; 3. comply with any of the following: - dyspnea, rr ≥ 30 times / min; - in resting state, transcutaneous oxygen saturation ≤ 93%; - oxygenation index (pao2 / fio2) < 300mmhg; 4. pulmonary imaging showed diffuse exudative lesions.

inclusion criteria: 1. age: 18-80 years old, male and female; 2. covid-19 confirmed cases; 3. comply with any of the following: - dyspnea, rr ≥ 30 times / min; - in resting state, transcutaneous oxygen saturation ≤ 93%; - oxygenation index (pao2 / fio2) < 300mmhg; 4. pulmonary imaging showed diffuse exudative lesions.