This multicentre pilot trial will assess the feasibility of a full-scale, randomized trial to determine whether bloodwork guided dosing of blood thinners reduces the risk of clotting in high-risk trauma patients. Patients will receive either standard of care dosing or dosing with adjustments based on bloodwork to achieve a minimum therapeutic threshold.

This multicentre pilot trial will assess the feasibility of a full-scale, randomized trial to determine whether anti-Xa guided dosing of low molecular heparin (LMWH) reduces the risk of venous thromboembolism (VTE) in high-risk trauma patients. Patients will receive either standard of care fixed dosing of Enoxaparin or 0.5 mg/kg twice daily with dose adjustments to achieve an anti-Xa trough level between 0.1 and 0.2 IU/mL.

Inclusion Criteria:

• Patients 18 years of age or older admitted to a hospital ward or intensive care unit following a traumatic injury involving two or more body systems (head, chest, abdomen, pelvis, extremity) and meeting at least one of the following high-risk criteria previously identified in a recent systematic review (1): age ≥ 65, body mass index ≥ 30 kg/m2, injury severity score ≥ 16, pelvic injury with activity restrictions, lower extremity injury with activity restrictions, or surgery during the index hospitalization.

To be eligible, patients must be deemed appropriate for pharmacologic prophylaxis by the most responsible physician and randomized with the intention to receive prophylaxis within 48 hours of admission. Prior to randomization, there is no restriction on whether or not patients have previously received pharmacologic or mechanical prophylaxis.

Exclusion Criteria:

1. Greater than 7 days since time of injury.
2. Requirement for therapeutic anticoagulation or dual-antiplatelet therapy
3. Unable or unwilling to receive pharmacologic prophylaxis within 48 hours of admission.
4. History of allergic reaction or sensitivity to LMWH.
5. Thrombocytopenia with platelets < 30.
6. Expected discharge or transfer from hospital within 72 hours.