Standard Fixed Enoxaparin Dosing Leads To Low Peak Anti-Factor Xa Levels In Microsurgical Free Flap Patients: A Pilot Study
Lee J. Varelas1, Shoshana Ambani2, Michael Gimbel2, Vu Nguyen2, Carolyn De La Cruz2, Jignesh Unadkat2, Tahsin O. Acaturk2, James Russavage2, Ernest K. Manders2, Mario Solari2.
1University of Pittsburgh School of Medicine, Pittsburgh, PA, USA, 2University of Pittsburgh Medical Center, Pittsburgh, PA, USA.
Background: Inadequate enoxaparin dosing for venous thromboembolism (VTE) chemoprophylaxis as determined by anti-factor Xa levels (aFXa) has been associated with increased risk of downstream VTE events in plastic surgery populations. Microsurgical free flap patients comprise a high-risk subpopulation, due to age, cancer diagnoses, and longer operative times. This pilot study investigates the adequacy of standard enoxaparin dosing for VTE prevention in patients undergoing free tissue transfer to the head and neck (H&N) and breast.
Method: An IRB-approved chart review of free flap patients with postoperative steady-state peak aFXA levels was performed (normal prophylactic aFXa range: 0.2-0.6). Patients were followed for 30-day VTE or bleeding events.
Results: Twenty eligible patients were identified (55% H&N, 45% breast). H&N patients received postoperative enoxaparin 30mg SQ BID, while breast patients received 40mg SQ daily. Average peak aFXa level was 0.11±0.08 (range <0.1-0.24). Only 17.6% of patients (N=3, all breast) attained peak aFXa levels within prophylactic range. BMI was the only significant predictor of peak aFXa levels (negative correlation, p=0.039). Accounting for BMI, total surgery time was the sole predictor of adequate prophylactic aFXa levels (p=0.001). There was one postoperative VTE event (5%, pulmonary embolism).
Conclusions: Standard enoxaparin dosing for VTE chemoprophylaxis in free flap patients appears to be inadequate, achieving appropriate aFXa levels in just a minority of patients. H&N patients are at greater risk than breast patients. Higher BMI and longer operative times were associated with lower aFXa levels. Free flap patients could benefit from personalized VTE prophylaxis regimens with enoxaparin dose-adjustments.
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