Extent of Surgical Injury Is Associated with Rate of Enoxaparin Metabolism: An Examination of Anti-Factor Xa Levels in Lower Extremity Free Flap Patients

Venous thromboembolism is a significant cause of morbidity and mortality among surgical patients.[1] Administration of a once daily or twice daily dose of enoxaparin during the perioperative period is an accepted method to prevent this life- or limb-threatening complication.[2] [3] However, recent studies examining multiple surgical populations have shown that a standard, “one size fits all” dose of enoxaparin does not produce sufficient levels of anticoagulation to prevent deep vein thromboembolism or pulmonary embolism in many patients.[4] [5] [6] [7] Studies in burn patients have shown that the total body surface area (TBSA) burned is associated with rapidity of enoxaparin metabolism; patients with larger TBSA required higher doses of enoxaparin.[4] [6] This is because extensive cutaneous injury produces a systemic inflammatory effect that increases drug metabolism.[4] Prior work in plastic and reconstructive surgery patients has shown that increased total body surface area surgically injured (TBSI), quantified with a Lund–Brower Chart, is associated with lower anti-factor Xa levels (aFXa); aFXa is a marker of enoxaparin activity and quantifies extent of anticoagulation. However, comparisons between patients have many confounders. The following case series examines the effect of TBSI on enoxaparin metabolism, using free flap patients as their controls. Lower extremity trauma patients who require initial debridement and later free flap surgeries can demonstrate how an increased TBSI may impact enoxaparin metabolism.

• References

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