This is a pilot study to determine if anti-thrombin III (AT-III) serum concentrations differ between patients with normal versus subtherapeutic anti-Xa trough concentrations when placed on enoxaparin 30 mg twice daily for VTE prophylaxis. Secondarily, this study will compare two enoxaparin dosing strategies.

This is a pilot study to determine if AT-III serum concentrations differ between patients with normal (>= 0.1 IU/mL) versus subtherapeutic (<0.1 IU/mL) anti-Xa trough concentrations when placed on enoxaparin 30 mg twice daily for venous thromboembolism (VTE) prophylaxis. Secondarily, this study will compare two enoxaparin dosing strategies: standard 30 mg twice daily and a dosing strategy based on trough anti-Xa values in high-risk trauma patients.

Specific aims include: 1) to compare the extent of reduced AT-III activity between patients with trough anti-Xa >= 0.1 IU/mL and < 0.1 IU/mL upon initial assay; 2) to determine the proportion of patients who reach goal anti-Xa and the time to goal anti-Xa achievement between two interventional dosing strategies: enoxaparin 40 mg every 12 hours (with consideration to increase to 50 mg every 12 hours if recheck anti-Xa is not at goal) and enoxaparin 30 mg every eight hours; 3) to compare anti-Xa enoxaparin dosing strategies based on VTE, bleeding rates, transfusion requirements, drug discontinuation rate and bioaccumulation, and 4) to determine patient-specific factors that correlate to subtherapeutic anti-Xa such as serial AT-III activity, weight, body mass index, age, cumulative fluid administration, and thromboelastography (TEG).

Inclusion Criteria:

• Multi-system trauma
• Anticipated length of stay of at least 72 hours
• At high risk (risk adjustment profile [RAP] >= 5) and initiated on enoxaparin 30 mg every 12 hours per VTE prophylaxis protocol
• No counterindication to trauma team VTE prophylaxis protocol (e.g., intracranial bleeding, incomplete spinal cord injury with hematoma within 24 hours post injury, ongoing hemorrhage, uncorrected coagulopathy, >= grade IV liver or spleen injury, intraocular injury)

Exclusion Criteria:

• Renal dysfunction (creatinine clearance < 30 mL/min or on continuous renal replacement therapy)
• Weight < 50 kg or > 150 kg
• Platelet count < 50,000
• Allergy to heparin or low molecular weight heparin
• On therapeutic anticoagulation on admission or requiring it within 24 hours of admission
• Isolated intracranial hemorrhage
• Known hyperbilirubinemia (serum bilirubin > 6.6 mg/dL)
• Pregnancy
• Incarceration

During patient enrollment up to 28 days, while inpatient

Underpowered; See full results and manuscript listed in citation section.