Since strategies were applied in intensive care medicine, including low tidal volume ventilation, fluid resuscitation, use of antibiotics, restrictive transfusion strategy and bundle of ventilator therapy, the incidence of Acute Respiratory Distress Syndrome (ARDS) has been decreased recent years. However, the mortality of severe ARDS is still higher to 45%. Few medications did were indicated to be effective in working on development of ARDS. Different with other disease, ARDS were difficult to prevent in its later stage like a domino effect. The medication interventions are all used after ARDS was developed, including ulinastatin. The investigators hypothesized that the key point in failure of medication therapy is the delay timing of medication intervention. If given the preventive strategy, such as ulinastatin, the incidence or the severity of ARDS might be decreased. Therefore this is a randomized controlled trial to test the hypothesis of the preventive effect of ulinastatin in ARDS.

This is a multi-center, randomized, double blinded, placebo controlled study.

Since strategies were applied in intensive care medicine, including low tidal volume ventilation, fluid resuscitation, use of antibiotics, restrictive transfusion strategy and bundle of ventilator therapy, the incidence of Acute Respiratory Distress Syndrome (ARDS) has been decreased recent years. However, the mortality of severe ARDS is still higher to 45%. Few medications did were indicated to be effective in working on development of ARDS. Different with other disease, ARDS were difficult to prevent in its later stage like a domino effect. The medication interventions are all used after ARDS was developed, including ulinastatin. The investigators hypothesized that the key point in failure of medication therapy is the delay timing of medication intervention. If given the preventive strategy, such as ulinastatin, the incidence or the severity of ARDS might be decreased.

Ulinastatin is a urinary trypsin inhibitor (UTI) that inhibits various inflammatory proteases has been widely used in China, Japan, and Korea for the treatment of patients with inflammatory disorders, postoperative organs protection, shock, and pancreatitis.

Therefore this is a randomized controlled trial to test the hypothesis of the preventive effect of ulinastatin in ARDS.

This is a multi-center, randomized, double blinded, placebo controlled study.

Inclusion Criteria:

• Patients should be more than 18 years old
• Patients are expected to living within 72 hours of ICU admission
• Patients' Lung Injury Prediction Score (LIPS) more than 4 and got at least 1 risk factors as below: bacteremia, sepsis or sepsis shock, pneumonia, multiple fractures, pulmonary contusion, aspiration, multiple blood transfusion, severe acute pancreatitis.

Exclusion Criteria: Patients will be excluded when they are

• diagnosed as ARDS
• without written informed consent
• with HIV infection
• with other immunologic deficiency (leukaemia, immune deficiency syndrome, etc)
• with organ transplantation or bone marrow transplantation
• with chronic pulmonary disease (except for Chronic Obstructive Pulmonary Disease (COPD) or asthma)
• with angitis
• with neutropenia (except for secondary to sepsis)
• using granulocyte-macrophage colony-stimulating factor or granulocyte colony-stimulating factor
• using asprin or clopidogrel
• using glucocorticoid
• withdrawing treatment
• treated by Xuebijing, thymosin, or intravenous immunoglobulin 1 month before enrollment
• enrolled in other clinical trials 3 months before enrollment
• being pregnancy
• being lactation

All data will be shared with other researchers in papers.