• Christopher J Pannucci, Kory I Fleming, Thomas K Varghese, John Stringham, Lyen C Huang, T Bartley Pickron, Ann Marie Prazak, Corinne Bertolaccini, and Arash Momeni.
• Plastic Surgery Northwest, Spokane, Washington.
• Ann. Surg. 2022 Dec 1; 276 (6): e682e690e682-e690.

ObjectiveTo examine the relationship between enoxaparin dose adequacy, quantified with anti-Factor Xa (aFXa) levels, and 90-day symptomatic venous thromboembolism (VTE) and postoperative bleeding.Summary Background DataSurgical patients often develop "breakthrough" VTE events-those which occur despite receiving chemical anticoagulation. We hypothesize that surgical patients with low aFXa levels will be more likely to develop 90-day VTE, and those with high aFXa will be more likely to bleed.MethodsPooled analysis of eight clinical trials (N = 985) from a single institution over a 4 year period. Patients had peak steady state aFXa levels in response to a known initial enoxaparin dose, and were followed for 90 days. Survival analysis log-rank test examined associations between aFXa level category and 90-day symptomatic VTE and bleeding.ResultsAmong 985 patients, 2.3% (n = 23) had symptomatic 90-day VTE, 4.2% (n = 41) had 90-day clinically relevant bleeding, and 2.1% (n = 21) had major bleeding. Patients with initial low aFXa were significantly more likely to have 90-day VTE than patients with adequate or high aFXa (4.2% vs 1.3%, P = 0.007). In a stratified analysis, this relationship was significant for patients who received twice daily (6.2% vs 1.5%, P = 0.003), but not once daily (3.0% vs 0.7%, P = 0.10) enoxaparin. No association was seen between high aFXa and 90-day clinically relevant bleeding (4.8% vs 2.9%, P = 0.34) or major bleeding (3.6% vs 1.6%, P = 0.18).ConclusionsThis manuscript establishes inadequate enoxaparin dosing as a plausible mechanism for breakthrough VTE in surgical patients, and identifies anticoagulant dose adequacy as a novel target for process improvement measures.Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.

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