Inclusion Criteria:Lung criteria:  Patients with severe Covid 19 nfection, from 18 to 75 years old, Invasive Mechanical Ventilation (IMV) Pao2 / fio2 less than 150 Non réponse to prone position Coagulation criteria ISTH score >5, D-dimer greater than 1200, Viscoelastic testing EXTEM A5 >65 FIBTEM > 30 and EXTEM ML<8%  -  Exclusion Criteria:  Ischemic CVD or presence of abnormal neurological examination. Active bleeding. Acute Myocardial Infarction within the previous three weeks or cardiac arrest during hospitalization.  cardiac tamponade. endocarditis. uncontrolled hypertension SBP> 185mmhg or DBP> 110. history of stage 4 cancer. history of brain tumor. Arterious venous malformation ruptured aneurysm. major surgery in the previous 2 weeks major trauma in the previous 2 weeks. pregnancy. fibrinogen less than 200 blood dyscrasias thrombocytopenia less than 30,000  -