The Safety and Dose Response Relationship of Ulinastatin for Acute Respiratory Distress Syndrome(ARDS)

Inclusion Criteria: 1. Have provided signed written informed consent form (ICF) from the patient or the patient's legal representative; 2. Male or Female patients ≥18 years of age; 3. ARDS defined with using 2012 Berlin Criteria; 4. ARDS diagnosed ≤7 days, and patients should be mechanically ventilated(invasive and or noninvasive mechanical ventilation); 5)100mmhg \< PaO2/FiO2 \< 250mmhg with CPAP/PEEP≥5 cmH2O; Exclusion Criteria: 1. Patient with known hypersensitivity to Ulinastatin/adjuvant or patient with allergic constitution; 2. Patients with artificial organs replacement therapy for liver or kidney； 3. Glasgow Coma Scale (GCS)≤8； 4. Cardiogenic pulmonary edema , and the cardiogenic pulmonary edema is as the only or primary reason for respiratory failure; 5. ARDS caused by burning, drowning, poisoning; 6. Presence of severe chronic liver diseases (Child-Pugh score 12-15)，or severe chronic respiratory disease with a PaCO2 \> 50 mmHg or the use of home oxygen; 7. Neutrophils\<1.5×10\^9/L 8. Moribund patients (i.e.,expected to live no longer than 24 hours) or with recent (within 7days or anytime during present hospitalization) cardiopulmonary arrest; 9. Patients need long-term glucocorticoid treatment or need to be treated with immunosuppressive drugs; 10. No intent/unwillingness to follow lung protective ventilation strategy or fluid management protocol; 11. Lung transplant patients; 12. Patients with malignancy, expected to live no longer than 6 months; 13. Pregnant or breast-feeding; 14. Patients who have participated in any clinical study within 3 months prior to the screening; 15. Any condition that in the opinion of the investigator would add the patient's risk or jeopardize the operation of the study.