* ards potentially caused by extra-pulmonary reasons, including non-pulmonary sepsis, pancreatitis, multiple trauma and massive transfusion, etc. * leukopenia (leukocyte count \<4,000/μl/) and/or thrombocytopenia (platelet count \<100,000/μl) * significant hepatic dysfunction, defined as elevated ast and alt ≥ 3 times the normal limits, or total bilirubin ≥ 1.5 mg/dl * severe renal insufficiency with serum creatinine \> 3.0 mg/dl * history of moderate to severe chronic lung disease requiring home-based oxygen therapy, including chronic obstructive pulmonary disease (copd), interstitial lung disease (ild), asthma and bronchiectasis, etc. * pre-existing peripheral nerve injury, spinal cord trauma, or neuromuscular disorder that may impair spontaneous ventilation (e.g., high cervical spinal cord injury, guillain-barré syndrome, and myasthenia gravis, etc.) * current diagnosis of pulmonary embolism * coexisting multi-organ failure, affecting more than 3 systems * combined with burn injury * life expectancy less than 6 months (e.g., due to an an end-stage malignant disease) * moribund and expected to die within 48 hours * known allergy to sivelestat or any of the study drug excipients * pregnancy or lactation, or the possibility of conception * current or recent (last 3 months) participation in any other clinical trial

* ards potentially caused by extra-pulmonary reasons, including non-pulmonary sepsis, pancreatitis, multiple trauma and massive transfusion, etc. * leukopenia (leukocyte count \<4,000/μl/) and/or thrombocytopenia (platelet count \<100,000/μl) * significant hepatic dysfunction, defined as elevated ast and alt ≥ 3 times the normal limits, or total bilirubin ≥ 1.5 mg/dl * severe renal insufficiency with serum creatinine \> 3.0 mg/dl * history of moderate to severe chronic lung disease requiring home-based oxygen therapy, including chronic obstructive pulmonary disease (copd), interstitial lung disease (ild), asthma and bronchiectasis, etc. * pre-existing peripheral nerve injury, spinal cord trauma, or neuromuscular disorder that may impair spontaneous ventilation (e.g., high cervical spinal cord injury, guillain-barré syndrome, and myasthenia gravis, etc.) * current diagnosis of pulmonary embolism * coexisting multi-organ failure, affecting more than 3 systems * combined with burn injury * life expectancy less than 6 months (e.g., due to an an end-stage malignant disease) * moribund and expected to die within 48 hours * known allergy to sivelestat or any of the study drug excipients * pregnancy or lactation, or the possibility of conception * current or recent (last 3 months) participation in any other clinical trial

ards potentially caused by extra-pulmonary reasons, including non-pulmonary sepsis, pancreatitis, multiple trauma and massive transfusion, etc. leukopenia (leukocyte count <4,000/μl/) and/or thrombocytopenia (platelet count <100,000/μl) significant hepatic dysfunction, defined as elevated ast and alt ≥ 3 times the normal limits, or total bilirubin ≥ 1.5 mg/dl severe renal insufficiency with serum creatinine > 3.0 mg/dl history of moderate to severe chronic lung disease requiring home-based oxygen therapy, including chronic obstructive pulmonary disease (copd), interstitial lung disease (ild), asthma and bronchiectasis, etc. pre-existing peripheral nerve injury, spinal cord trauma, or neuromuscular disorder that may impair spontaneous ventilation (e.g., high cervical spinal cord injury, guillain-barré syndrome, and myasthenia gravis, etc.) current diagnosis of pulmonary embolism coexisting multi-organ failure, affecting more than 3 systems combined with burn injury life expectancy less than 6 months (e.g., due to an an end-stage malignant disease) moribund and expected to die within 48 hours known allergy to sivelestat or any of the study drug excipients pregnancy or lactation, or the possibility of conception current or recent (last 3 months) participation in any other clinical trial

ards potentially caused by extra-pulmonary reasons, including non-pulmonary sepsis, pancreatitis, multiple trauma and massive transfusion, etc. leukopenia (leukocyte count <4,000/μl/) and/or thrombocytopenia (platelet count <100,000/μl) significant hepatic dysfunction, defined as elevated ast and alt ≥ 3 times the normal limits, or total bilirubin ≥ 1.5 mg/dl severe renal insufficiency with serum creatinine > 3.0 mg/dl history of moderate to severe chronic lung disease requiring home-based oxygen therapy, including chronic obstructive pulmonary disease (copd), interstitial lung disease (ild), asthma and bronchiectasis, etc. pre-existing peripheral nerve injury, spinal cord trauma, or neuromuscular disorder that may impair spontaneous ventilation (e.g., high cervical spinal cord injury, guillain-barré syndrome, and myasthenia gravis, etc.) current diagnosis of pulmonary embolism coexisting multi-organ failure, affecting more than 3 systems combined with burn injury life expectancy less than 6 months (e.g., due to an an end-stage malignant disease) moribund and expected to die within 48 hours known allergy to sivelestat or any of the study drug excipients pregnancy or lactation, or the possibility of conception current or recent (last 3 months) participation in any other clinical trial