Enoxaparin at Prophylactic or Therapeutic Doses in COVID-19

Inclusion Criteria: * COVID-19 related pneumonia with moderate-severe respiratory failure (PaO2/FiO2\<250) and/or markedly increased D-dimer level (\>2000 ng/mL) * Signed informed consent Exclusion Criteria: * age \< 18 and \> 80 yrs * history of bleeding (peptic ulcer, esophageal varices, cerebral aneurysm, cancer at high risk of bleeding, cirrhosis, hemorrhagic stroke \< 1 year) * thrombocytopenia (\<100 x109/L) * anemia (Hb \< 8 g/dl) * coagulation abnormalities (PT e/o aPTT \> 1.5; fibrinogen \< 150 mg/dl) * consumption coagulopathy (ISTH criteria) \[15, 16\] * deep vein thrombosis or pulmonary embolism * dual antiplatelet therapy * ongoing anticoagulant therapy * allergic reaction to LMWH * previous heparin-induced thrombocytopenia * major surgery \< 1 month; neurosurgery \<3 months; eye surgery \<3 months * pregnancy * arterial hypertension (SBPS\>160 mm Hg; DBP\>100 mm Hg) * renal failure (creatinine clearance 30 ml/min) * ICU admission or endotracheal intubation