- allergy to heparin - any history of heparin-induced thrombocytopenia - high risk of bleeding (platelet count < 50,000/µl or international normalized ratio > 1.5) - patients with known bleeding disorders (i.e. hemophilia or von willebrand disease) - active bleeding - pulmonary bleeding during this hospital admission (pulmonary bleeding is frank bleeding in the lungs, trachea or bronchi with repeated hemoptysis, or requiring repeated suctioning, and temporally associated with acute deterioration in respiratory status) - neurosurgical procedures during this hospital admission or such procedures are planned - epidural catheter in place - any history of intracranial, spinal or epidural hemorrhage - tracheostomy in place - cervical spinal cord injury associated with reduced long-term ability to breathe independently - spinal or peripheral nerve disease with a likely prolonged reduction in the ability to breathe independently - receiving extra-corporeal membrane oxygenation or continuous renal replacement therapy - usually treated with hemodialysis or peritoneal dialysis for end-stage renal failure - death is deemed imminent or inevitable or there is an underlying disease with a life expectancy of fewer than 90 days - pregnant or might be pregnant. - objection from the treating clinician - consent refused by the patient or substitute decision maker. - history of thrombosis (vte or cardiovascular event)

- allergy to heparin - any history of heparin-induced thrombocytopenia - high risk of bleeding (platelet count < 50,000/µl or international normalized ratio > 1.5) - patients with known bleeding disorders (i.e. hemophilia or von willebrand disease) - active bleeding - pulmonary bleeding during this hospital admission (pulmonary bleeding is frank bleeding in the lungs, trachea or bronchi with repeated hemoptysis, or requiring repeated suctioning, and temporally associated with acute deterioration in respiratory status) - neurosurgical procedures during this hospital admission or such procedures are planned - epidural catheter in place - any history of intracranial, spinal or epidural hemorrhage - tracheostomy in place - cervical spinal cord injury associated with reduced long-term ability to breathe independently - spinal or peripheral nerve disease with a likely prolonged reduction in the ability to breathe independently - receiving extra-corporeal membrane oxygenation or continuous renal replacement therapy - usually treated with hemodialysis or peritoneal dialysis for end-stage renal failure - death is deemed imminent or inevitable or there is an underlying disease with a life expectancy of fewer than 90 days - pregnant or might be pregnant. - objection from the treating clinician - consent refused by the patient or substitute decision maker. - history of thrombosis (vte or cardiovascular event)