inclusion criteria: 1. age ≥18 years; 2. the laboratory (rt-pcr) confirmed the diagnosis of severe patients infected with covid-19 (refer to the fifth edition of the chinese diagnosis and treatment guideline for trial); the diagnosis of new coronavirus pneumonia was confirmed, and any of the following: 1) respiratory distress, breathing ≥30 beats / min; 2) in the resting state, the oxygen saturation is ≤93%; 3) arterial blood oxygen partial pressure / oxygen concentration ≤300mmhg 3. the diagnosis is less than or equal to 12 days;

inclusion criteria: 1. age ≥18 years; 2. the laboratory (rt-pcr) confirmed the diagnosis of severe patients infected with covid-19 (refer to the fifth edition of the chinese diagnosis and treatment guideline for trial); the diagnosis of new coronavirus pneumonia was confirmed, and any of the following: 1) respiratory distress, breathing ≥30 beats / min; 2) in the resting state, the oxygen saturation is ≤93%; 3) arterial blood oxygen partial pressure / oxygen concentration ≤300mmhg 3. the diagnosis is less than or equal to 12 days;

inclusion criteria: age ≥18 years; the laboratory (rt-pcr) confirmed the diagnosis of severe patients infected with covid-19 (refer to the fifth edition of the chinese diagnosis and treatment guideline for trial); the diagnosis of new coronavirus pneumonia was confirmed, and any of the following: 1) respiratory distress, breathing ≥30 beats / min; 2) in the resting state, the oxygen saturation is ≤93%; 3) arterial blood oxygen partial pressure / oxygen concentration ≤300mmhg the diagnosis is less than or equal to 12 days;

inclusion criteria: age ≥18 years; the laboratory (rt-pcr) confirmed the diagnosis of severe patients infected with covid-19 (refer to the fifth edition of the chinese diagnosis and treatment guideline for trial); the diagnosis of new coronavirus pneumonia was confirmed, and any of the following: 1) respiratory distress, breathing ≥30 beats / min; 2) in the resting state, the oxygen saturation is ≤93%; 3) arterial blood oxygen partial pressure / oxygen concentration ≤300mmhg the diagnosis is less than or equal to 12 days;

inclusion criteria: 1. age ≥18 years; 2. the laboratory (rt-pcr) confirmed the diagnosis of severe patients infected with covid-19 (refer to the fifth edition of the chinese diagnosis and treatment guideline for trial); the diagnosis of new coronavirus pneumonia was confirmed, and any of the following: 1) respiratory distress, breathing ≥30 beats / min; 2) in the resting state, the oxygen saturation is ≤93%; 3) arterial blood oxygen partial pressure / oxygen concentration ≤300mmhg 3. the diagnosis is less than or equal to 12 days;

inclusion criteria: 1. age ≥18 years; 2. the laboratory (rt-pcr) confirmed the diagnosis of severe patients infected with covid-19 (refer to the fifth edition of the chinese diagnosis and treatment guideline for trial); the diagnosis of new coronavirus pneumonia was confirmed, and any of the following: 1) respiratory distress, breathing ≥30 beats / min; 2) in the resting state, the oxygen saturation is ≤93%; 3) arterial blood oxygen partial pressure / oxygen concentration ≤300mmhg 3. the diagnosis is less than or equal to 12 days;