Insufficient dosing of enoxaparin is common in patients post-orthopedic surgery and increases the risk of thromboembolic disease

Introduction

Deep vein thrombosis is a serious complication of orthopedic and traumatological surgical procedures. Operations with the highest risk of developing deep vein thrombosis include extensive procedures on the lower limbs and pelvis, especially total hip and knee replacement, but also trauma surgeries, particularly acute osteosyntheses, as well as procedures addressing complications such as pseudoarthrosis.

Currently, the gold standard for perioperative prophylaxis of thromboembolic disease is the administration of low molecular weight heparins. The presented study focused on the issue of underdosing enoxaparin in patients undergoing surgery in the pelvis and lower limbs area and the subsequent risk of developing thromboembolic disease.

Study Progress and Results

Patients undergoing acute surgery in the pelvis and lower extremities due to a fracture or a procedure to address pseudoarthrosis in the same area were included in the prospective study. The patients were administered enoxaparin at a dose of 30 mg twice daily as prophylaxis for thromboembolic disease. An anti-Xa level examination with a target range of 0.2–0.4 IU/ml was performed. If this level was not reached, the dose of enoxaparin was adjusted by increasing it by 10 mg, followed by a control anti-Xa examination.

A total of 109 patients participated in the study, and 43% of them showed insufficient anti-Xa levels (< 0.2 IU/ml) with standard dosing of enoxaparin. Low levels were predicted by higher body weight, surgical procedures involving the acetabulum, and the duration of the surgical procedure (p < 0.001, 0.006, and 0.004, respectively). Adjusting the dosing of enoxaparin contributed to an increase in the proportion of patients who reached the target anti-Xa level, rising to 87.8% (p < 0.001).

For patients with insufficient anti-Xa activity levels during hospitalization or at discharge, there was a significant increase in the rate of developing thromboembolic disease within 90 days following the procedure compared to patients with anti-Xa activity within the prophylactic range (deep vein thrombosis 12 vs. 1.36%; p = 0.023; pulmonary embolism 8 vs. 0%; p = 0.027). No cases of severe bleeding were observed during the study.

Conclusion

The study indicates that standard dosing of enoxaparin in patients undergoing surgery in the pelvis and lower limbs is often associated with insufficient anti-Xa activity levels and an increased risk of thromboembolic disease within the following 90 days.

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Source: Jones D. L., Jones W. A., Fleming K. I. Underdosing of prophylactic enoxaparin is common in orthopaedic trauma and predicts 90-day venous thromboembolism. J Orthop Trauma 2019 Nov; 33 (11): 570–576, doi: 10.1097/BOT.0000000000001563.