Patient description: The patient is a 23-year-old man who came to the hospital with high blood pressure (175/95 mmHg) and signs of septicemia. He developed respiratory failure requiring mechanical ventilation and renal failure requiring hemodialysis. His blood smear showed microangiopathic hemolytic anemia and thrombocytopenia. His blood tests revealed elevated lactate dehydrogenase and reduced human complement C3 levels with a normal coagulation profile. He was diagnosed with atypical hemolytic uremic syndrome. He was treated with plasma exchange and corticosteroids. He has been previously vaccinated with meningococcal group ACWY conjugate vaccine and meningococcal group B vaccine. The genetic survey revealed ADAMTS13 >10%.

Clinical trial eligibility criteria: eligible ages (years): 16.0-999.0,  Acute Respiratory Distress Syndrome (ARDS caused by Non-COVID-19 cohort) At Informed Consent 1. Patients with ARDS confirmed by the Berlin definition based on the following diagnostic (a)-(d): 1. Patients within 7 days from invasion or exacerbation of respiratory symptoms or acute onset of ARDS. 2. Patients with respiratory failure not fully explained by cardiac failure or fluid overload; Need objective assessment (e. g., echo-cardiography) to hydrostatic edema if no risk factor present 3. Patients with bilateral opacities not fully explained by effusions, lobar/ lung collapse, or nodules on chest X-ray or CT scan 4. Patients with PaO2/ FiO2 ratio ≤ 300 mmHg (PEEP ≥ 5 cmH2O) 2. Patients who are intubated and mechanically ventilated 3. Patients who can be enrolled in the study within 48 hours after ARDS diagnosis confirmed by Berlin definition 4. Patients aged ≥ 16 years at informed consent (Signed informed consent form from legally acceptable representative must be available if patient is aged < 20 years) At Enrollment 1. Patients with PaO2/ FiO2 ratio ≥ 50 mmHg and ≤ 200 mmHg (PEEP ≥ 5 cmH2O) 2. Patients with bilateral opacities not fully explained by effusions, lobar/ lung collapse, or nodules on CT scan within 48 hours before enrollment 3. Patients who are intubated and mechanically ventilated 4. Patients who can be enrolled in the study within 48 hours after ARDS diagnosis confirmed by Berlin definition  At Informed Consent 1. Patients with mechanical ventilation for more than 48 hours prior to ARDS diagnosis confirmed by Berlin definition 2. Patients who are considered to be extremely unlikely to withdraw from mechanical ventilation 3. Patients who are treated with ECMO or HFOV 4. Patients with renal dialysis therapy for chronic renal failure 5. Patients with congestive heart failure (NYHA class IV) 6. Patients with acuter left ventricular failure 7. Patients with liver failure (Child-Pugh grade C) 8. Patients who have burns in excess of 15% total body surface area 9. Patients after resuscitation from cardiac arrest 10. Patients with a history of hypersensitivity to the anticoagulants (Heparin or Nafamostat mesylate) 11. Patients who have received cytapheresis, blood purification therapy with cytokine adsorbing devices or endotoxin removal therapy within 7 days prior to informed consent 12. Patients with pregnancy or lactating 13. Patients tested positive for COVID-19 At Enrollment 1. Patients who are considered to be extremely unlikely to withdraw from mechanical ventilation 2. Patients who are treated with ECMO or HFOV after obtaining informed consent prior to enrollment 3. Patients with platelet count ≤ 50,000 /mm3 by the latest blood test 4. Patients who have received cytapheresis, blood purification therapy with cytokine adsorbing devices or endotoxin removal therapy between informed consent and enrollment 5. Patients whose life expectancy is ≤ 24 hours after enrollment 6. Patients after resuscitation from cardiac arrest between informed consent and enrollment 7. Patients tested positive for COVID-19 between informed consent and enrollment (ARDS caused by COVID-19 cohort) At Informed Consent 1. Patients tested positive for COVID-19 2. Patients with ARDS confirmed by the Berlin definition based on the following diagnostic (a)-(d): 1. Patients within 7 days from invasion or exacerbation of respiratory symptoms or acute onset of ARDS. 2. Patients with respiratory failure not fully explained by cardiac failure or fluid overload; Need objective assessment (e. g., echo-cardiography) to hydrostatic edema if no risk factor present 3. Patients with bilateral opacities not fully explained by effusions, lobar/ lung collapse, or nodules on chest X-ray or CT scan 4. Patients with PaO2/ FiO2 ratio ≤ 300 mmHg (PEEP ≥ 5 cmH2O) 3. Patients who are intubated and mechanically ventilated 4. Patients who can be enrolled in the study within 48 hours after ARDS diagnosis confirmed by Berlin definition 5. Patients aged ≥ 16 years at informed consent (Signed informed consent form from legally acceptable representative must be available if patient is aged < 20 years) At Enrollment 1. Patients with PaO2/ FiO2 ratio ≥ 50 mmHg and ≤ 200 mmHg (PEEP ≥ 5 cmH2O) 2. Patients who are intubated and mechanically ventilated 3. Patients who can be enrolled in the study within 48 hours after ARDS diagnosis confirmed by Berlin definition At Informed Consent 1. Patients with mechanical ventilation for more than 48 hours prior to ARDS diagnosis confirmed by Berlin definition 2. Patients who are considered to be extremely unlikely to withdraw from mechanical ventilation 3. Patients who are treated with ECMO or HFOV 4. Patients with renal dialysis therapy for chronic renal failure 5. Patients with congestive heart failure (NYHA class IV) 6. Patients with acuter left ventricular failure 7. Patients with liver failure (Child-Pugh grade C) 8. Patients who have burns in excess of 15% total body surface area 9. Patients after resuscitation from cardiac arrest 10. Patients with a history of hypersensitivity to the anticoagulants (Heparin or Nafamostat mesylate) 11. Patients who have received cytapheresis, blood purification therapy with cytokine adsorbing devices or endotoxin removal therapy within 7 days prior to informed consent 12. Patients with pregnancy or lactating At Enrollment 1. Patients who are considered to be extremely unlikely to withdraw from mechanical ventilation 2. Patients who are treated with ECMO or HFOV after obtaining informed consent prior to enrollment 3. Patients with platelet count ≤ 50,000 /mm3 by the latest blood test 4. Patients who have received cytapheresis, blood purification therapy with cytokine adsorbing devices or endotoxin removal therapy between informed consent and enrollment 5. Patients whose life expectancy is ≤ 24 hours after enrollment 6. Patients after resuscitation from cardiac arrest between informed consent and enrollment