Low Anti-Factor Xa Level Predicts 90-Day Symptomatic Venous Thromboembolism in Surgical Patients Receiving Enoxaparin Prophylaxis: A Pooled Analysis of Eight Clinical Trials

Unfractionated Heparins, Low-Molecular-Weight Heparins, and Indirect Factor Xa Inhibitors in Plastic and Reconstructive Surgery: An Evidence-Based Review

SUMMARY

Venous thromboembolism can present with devastating complications and sequalae, particularly in the surgical patient. Current data support prophylactic anticoagulant use in high-risk hospitalized patients, defined as those with a Caprini Risk Assessment Model score of 7 or greater. The most frequently used chemoprophylaxis agents include unfractionated heparin, low-molecular-weight heparin, and indirect factor Xa inhibitors. The authors review the mechanisms of action, metabolism, reversal agents, indications, contraindications, advantages, and disadvantages of these medications in plastic and reconstructive surgery.

Impact of Reduced Enoxaparin Prophylactic Dosing on Bleeding and Thrombotic Risk for Low Body Weight Post-Operative Colorectal Surgery Patients

Introduction: Colorectal surgery (CORS) patients are at the highest risk of any general surgery population for the development of post-operative venous thromboembolism (VTE) and are also at an increased risk for post-operative bleeding, especially with procedures related to early cancer stages. Low molecular weight heparin (LMWH) is recommended for VTE prophylaxis in this surgical population. Current guidelines and primary literature along with institutional protocols support dosage adjustments for obesity and impaired renal function, but literature providing optimal VTE prophylactic LMWH dosing is extremely limited for underweight, surgical patients. Objectives: The aim of this study was to evaluate both bleeding and VTE rates for hospitalized underweight colorectal surgery patients receiving post-operative VTE prophylaxis with standard enoxaparin 40 mg subcutaneously (SQ) every 24 hours versus reduced dose enoxaparin 30 mg SQ every 24 hours. Methods: This trial was a multicenter, retrospective chart review with data collected on post-operative CORS patients over a 10-year period. Patients were included if aged 18 years and older, weighed less than 50 kg, and received at least 1 dose of enoxaparin 40 mg or 30 mg post-operatively. The primary endpoint was a descriptive comparison of post-operative bleeding with use of standard enoxaparin 40 mg SQ every 24 hours compared to reduced dose enoxaparin 30 mg SQ every 24 hours for post-operative VTE prophylaxis. The secondary endpoint was the descriptive comparison of post-operative thrombotic event rates in the same population. Results: The total population investigated included 146 patients. One hundred twenty-nine (88.4%) received standard enoxaparin and 17 (11.6%) received reduced enoxaparin. Overall, 9 bleeding events (7.0%) and 2 major VTE events (1.6%) occurred, all within the standard enoxaparin group. Conclusion: Standard dose enoxaparin for post-operative VTE prophylaxis demonstrated increased bleeding and thrombotic events requiring medical and surgical intervention in comparison to reduced dose enoxaparin for low body weight CORS patients. The results of this study are hypothesis generating and continued research involving more robust systematic reviews are needed to evaluate both safety and efficacy of reduced VTE prophylaxis with LMWH in the underweight, surgical patient population.

Incidence of Venous Thromboembolism Based on Caprini Score in Deep Inferior Epigastric Perforator Flap Breast Reconstruction

BACKGROUND

 Deep inferior epigastric perforator (DIEP) flaps are commonly used for autologous breast reconstruction, but reported rates of venous thromboembolism (VTE) are up to 6.8%. This study aimed to determine the incidence of VTE based on preoperative Caprini score following DIEP breast reconstruction.

METHODS

 This retrospective study included patients who underwent DIEP flaps for breast reconstruction between January 1, 2016 and December 31, 2020 at a tertiary-level, academic institution. Demographics, operative characteristics, and VTE events were recorded. Receiver operating characteristic analysis was performed to determine the area under the curve (AUC) of the Caprini score for VTE. Univariate and multivariate analyses assessed risk factors associated with VTE.

RESULTS

 This study included 524 patients (mean age 51.2 ± 9.6 years). There were 123 (23.5%) patients with the Caprini score of 0 to 4, 366 (69.8%) with scores 5 to 6, 27 (5.2%) with scores 7 to 8, and 8 (1.5%) patients with scores >8. Postoperative VTE occurred in 11 (2.1%) patients, at a median time of 9 days (range 1-30) after surgery. VTE incidence by the Caprini score was 1.9% for scores 3 to 4, 0.8% for scores 5 to 6, 3.3% for scores 7 to 8, and 13% for scores >8. The Caprini score achieved an AUC of 0.70. A Caprini score >8 was significantly predictive of VTE on multivariable analysis relative to scores 5 to 6 (odds ratio = 43.41, 95% confidence interval = 7.46-252.76, p < 0.001).

CONCLUSION

 In patients undergoing DIEP breast reconstruction, VTE incidence was highest (13%) in Caprini scores greater than eight despite chemoprophylaxis. Future studies are needed to assess the role of extended chemoprophylaxis in patients with high Caprini scores.

Extended thromboprophylaxis post gynaecological cancer surgery; the effect of weight adjusted and fixed dose LMWH (Tinzaparin)

OBJECTIVE

Gynaecological cancer surgery is associated with high rates of venous thromboembolism (VTE) despite recommended prophylaxis. We sought to investigate the impact of extended prophylaxis with fixed dose and weight based LMWH in patients undergoing gynaecological cancer surgery.

METHODS

VTE rates were recorded in patients who received LMWH prophylaxis (4500 IU Tinzaparin once daily) for the duration of hospital stay (2006-2012) (n = 610) and were compared with VTE rates in patients who underwent surgery after the introduction of extended prophylaxis (3500/4500 IU Tinzaparin for patients with BMI < 40kg/m2 and 75 IU/kg for BMI > 40 kg/m2) (2012-2017) (n = 651). Peak (4 h) anti-Xa levels in a subset of patients were also evaluated.

RESULTS

73 (5.7%) cases of VTE were recorded during 1 year of follow-up. 20 cases occurred during hospital stay. There was no significant difference in the rate of VTE between the extended prophylaxis cohort and the standard prophylaxis cohort. 23/24 patients who developed VTE in the extended prophylaxis cohort received a fixed (4500 units) dose of Tinzaparin. 63% of patients who received a fixed LMWH dose had peak anti-Xa levels below the target range (0.2-0.4 IU/ml). Peak anti-Xa was lower in patients who subsequently developed VTE compared with those who received either fixed dose (P = 0.041) and weight adjusted Tinzaparin (P = 0.0006).

CONCLUSIONS

Extended prophylaxis with Tinzaparin does not significantly reduce VTE rates in gynaecological cancer patients post surgery. Peak anti-Xa levels may be suboptimal in many patients receiving a fixed LMWH dose. Further studies are required to determine whether weight adjusted doses of Tinzaparin may provide more effective prophylaxis following gynaecological cancer surgery.

Prevention of Venous Thromboembolism in Microvascular Surgery Patients Using Weight-Based Unfractionated Heparin Infusions

BACKGROUND

 Unfractionated heparin infusions are commonly used in microvascular surgery to prevent microvascular thrombosis. Previously, fixed-dose heparin infusions were believed to provide sufficient venous thromboembolism (VTE) prophylaxis; however, we now know that this practice is inadequate for the majority of patients. Anti-factor Xa (aFXa) level is a measure of unfractionated heparin efficacy and safety. This study evaluated the pharmacodynamics of weight-based dose heparin infusions and the impacts of real-time aFXa-guided heparin dose adjustments.

METHODS

 This prospective clinical trial enrolled adult microvascular surgery patients who received a weight-based heparin dose following a microsurgical procedure. Steady-state aFXa levels were monitored, and patients with out-of-range levels received dose adjustments. The study outcomes assessed were aFXa levels at a dose of heparin 10 units/kg/hour, time to adequate aFXa level, number of dose adjustments required to reach in-range aFXa levels, and clinically relevant bleeding and VTE at 90 days.

RESULTS

 Twenty-one patients were prospectively recruited, and usable data were available for twenty patients. Four of twenty patients (20%) had adequate prophylaxis at a heparin dose of 10 units/kg/hour. Among patients who received dose adjustments and achieved in-range aFXa levels, the median number of dose adjustments was 2 and the median weight-based dose was 11 units/kg/hour. The percentage of patients with in-range levels was significantly increased (65 vs. 15%, p = 0.0002) as a result of real-time dose adjustments. The rate of VTE at 90 days was 0%, and clinically relevant bleeding rate at 90 days was 15%.

CONCLUSION

 Weight-based heparin infusions at a rate of 10 units/kg/hour provide a detectable level of anticoagulation for some patients following microsurgical procedures, but most patients require dose adjustment to ensure adequate VTE prophylaxis.