Standard prophylactic enoxaparin dosing leads to inadequate anti-Xa levels and increased deep venous thrombosis rates in critically ill trauma and surgical patients

J Trauma. 2010 Apr;68(4):874-80. doi: 10.1097/TA.0b013e3181d32271.


Background: Deep venous thromboses (DVT) continue to cause significant morbidity in critically ill patients. Standard prophylaxis for high risk patients includes twice-daily dosing with 30 mg enoxaparin. Despite prophylaxis, DVT rates still exceed 10% to 15%. Anti-Xa levels are used to measure the activity of enoxaparin and 12-hour trough levels <or=0.1 IU/mL have been associated with higher rates of DVT in orthopedic patients. We hypothesized that low Anti-Xa levels would be found in critically ill trauma and surgical patients and that low levels would be associated with higher rates of DVT.

Methods: All patients on the surgical intensive care unit (ICU) service were prospectively followed. In the absence of contraindications, patients were given prophylactic enoxaparin and anti-Xa levels were drawn after the third dose. Trough levels <or=0.1 IU/mL were considered low. Screening duplex exams were obtained within 48 hours of admission and then weekly. Patients were excluded if they did not receive a duplex, if they had a prior DVT, or if they lacked correctly timed anti-Xa levels. DVT rates and demographic data were compared between patients with low and normal anti-Xa levels.

Results: Data were complete for 54 patients. Eighty-five percent suffered trauma (Injury Severity Score of 25 +/- 12) and 74% were male. Overall, 27 patients (50%) had low anti-Xa levels. Patients with low anti-Xa levels had significantly more DVTs than those with normal levels (37% vs. 11%, p = 0.026), despite similar age, body mass index, Injury Severity Score, creatinine clearance, high risk injuries, and ICU/ventilator days.

Conclusion: Standard dosing of enoxaparin leads to low anti-Xa levels in half of surgical ICU patients. Low levels are associated with a significant increase in the risk of DVT. These data support future studies using adjusted-dose enoxaparin.

MeSH terms

  • Adult
  • Anticoagulants / administration & dosage*
  • Anticoagulants / pharmacokinetics*
  • Enoxaparin / administration & dosage*
  • Enoxaparin / pharmacokinetics*
  • Factor Xa / metabolism*
  • Female
  • Humans
  • Injury Severity Score
  • Male
  • Prospective Studies
  • Risk Factors
  • Ultrasonography, Doppler, Duplex
  • Venous Thrombosis / diagnostic imaging
  • Venous Thrombosis / prevention & control*
  • Wounds and Injuries / blood
  • Wounds and Injuries / complications
  • Wounds and Injuries / surgery


  • Anticoagulants
  • Enoxaparin
  • Factor Xa