Fixed Versus Weight-Based Enoxaparin Dosing in Thoracic Surgery Patients

VTE encompasses deep venous thrombosis and pulmonary embolus and is the proximate cause of death in over 100,000 hospitalized patients per year 4,5. To put this in better context, VTE kills more people each year than the annual morbidity from motor vehicle crashes and breast cancer combined-and one third of these deaths are known to occur after surgical procedures 34. "Breakthrough" VTE events occur in patients despite the receipt of guideline-compliant chemical prophylaxis. These events can be frustrating for surgeons, can represent a resource and financial burden for hospital systems, and most importantly, can be life or limb threatening for patients.

Existing data from our group and others suggests that inadequate enoxaparin dosing, quantified by aFXa levels, represents a plausible explanatory mechanism for "breakthrough" VTE events that occur among thoracic surgery patients. This project will examine the pharmacodynamics of fixed dose enoxaparin (40mg/day) after VATS-this dose and frequency were the most commonly prescribed VTE chemical prophylaxis strategy in a recent survey of thoracic surgeons 35. If inadequate aFXa levels are observed with fixed enoxaparin dosing, the study will design, implement and test a weight-based dosing approach to optimize aFXa levels. The study will also examine how alteration of enoxaparin dose magnitude affects peak aFXa levels and risk for VTE and major bleeding events.

Aim 1: To evaluate peak steady-state aFXa levels in response to a fixed dose of enoxaparin prophylaxis (40mg once daily) in VATS patients.

Rationale: Over 12% of thoracic surgery patients have "breakthrough" VTE events despite receipt of fixed dose chemical prophylaxis 29. Fixed dose enoxaparin prophylaxis has been shown to be inadequate for the majority of patients in other surgical subspecialties.

Hypothesis: Peak steady state aFXa levels will be within the accepted range (0.3-0.5 IU/mL) in 40% of patients after VATS.

Aim 2: To compare the effect of fixed (40mg once daily) and weight-based (0.5mg/kg once daily) enoxaparin prophylaxis on peak steady state aFXa levels after VATS.

Rationale: Our preliminary data shows a potential association between body weight and aFXa levels in response to fixed dosing; this will be confirmed using a multi-center approach in Aim #1. Body weight may be an important predictor of appropriate enoxaparin dose.

Hypothesis: Weight-based enoxaparin prophylaxis, when compared to fixed dose prophylaxis, will increase the proportion of patients with in-range peak aFXa levels from 40% to 80%.

Aim 3: To examine rates of 90-day VTE and clinically relevant bleeding events in VATS patients who receive fixed dose vs. weight-based enoxaparin prophylaxis.

Rationale: This observational Aim will allow us to better understand VTE and bleeding rates after VATS. Since these are rare events it is impossible to power the study to detect increases or decreases in risk between the dose groups. This study does provide a way to demonstrate an unexpected, very large difference in risk.

Hypothesis: Rates of post-operative VTE and clinically relevant bleeding will be less than 2% in each group.

• Fixed Dose Enoxaparin (Drug): Eligible patients will be administered 40 mg enoxaparin daily and will have steady state peak and trough anti-Xa levels drawn after the third enoxaparin dose. For patients in-range (levels 0.3-0.5IUmL), no intervention will be undertaken. For patients out of range, enoxaparin dose will be adjusted according to an established dose adjustment algorithm. Repeat levels will be checked after the third administration of the new dose.
• Variable Dose Enoxaparin (Drug): Eligible patients will be administered 0.5 mg/kg enoxaparin daily and will have steady state peak and trough anti-Xa levels drawn after the third enoxaparin dose. For patients in-range (levels 0.3-0.5IUmL), no intervention will be undertaken. For patients out of range, enoxaparin dose will be adjusted according to an established dose adjustment algorithm. Repeat levels will be checked after the third administration of the new dose.

Primary outcomes

• Number of Patients With in Range Initial Peak Xa Level [36 hours]: Number of patients with in range initial peak Xa level

Secondary outcomes

• Number of Participants With Venous Thromboembolism Events or Death [90 days]: Any symptomatic venous thromboembolism events, including deep venous thrombosis or pulmonary embolus occurring within 90 days of surgery
• Number of Participants With Bleeding Events [90 days]: Bleeding events requiring alteration in the course of care within 90 days of surgery

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* receiving Video-Assisted Thoracoscopic Surgery
* able to have Enoxaparin initiated within 8 hours after procedure

Exclusion Criteria:

* Contraindication to use of enoxaparin
* Intracranial bleeding/stroke
* Hematoma or bleeding disorder
* Heparin-induced thrombocytopenia positive
* Creatinine clearance less than or equal to 30 mL/min
* Serum creatinine greater than 1.6 mg/dL
* Epidural catheter

Participant flow

Outcome results

• Number of Patients With in Range Initial Peak Xa Level (Primary), Count of participants, Participants: Fixed Dose Enoxaparin 27; Weight Tiered Enoxaparin 27
• Number of Participants With Venous Thromboembolism Events or Death (Secondary), Count of participants, Participants: Fixed Dose Enoxaparin 1; Weight Tiered Enoxaparin 0
• Number of Participants With Bleeding Events (Secondary), Count of participants, Participants: Fixed Dose Enoxaparin 1; Weight Tiered Enoxaparin 3

Adverse events

Time frame: 90 days

Serious adverse events by term

Other adverse events by term

• Results publication: Pannucci CJ, Fleming KI, Varghese TK Jr, Stringham J, Huang LC, Pickron TB, Prazak AM, Bertolaccini C, Momeni A. Low Anti-Factor Xa Level Predicts 90-Day Symptomatic Venous Thromboembolism in Surgical Patients Receiving Enoxaparin Prophylaxis: A Pooled Analysis of Eight Clinical Trials. Ann Surg. 2022 Dec 1;276(6):e682-e690. doi: 10.1097/SLA.0000000000004589. Epub 2020 Oct 19. PMID 33086312
• Results publication: Pannucci CJ, Fleming KI, Bertolaccini C, Moulton L, Stringham J, Barnett S, Lin J, Varghese TK Jr. Fixed or Weight-Tiered Enoxaparin After Thoracic Surgery for Venous Thromboembolism Prevention. Ann Thorac Surg. 2020 Jun;109(6):1713-1721. doi: 10.1016/j.athoracsur.2019.12.058. Epub 2020 Feb 8. PMID 32045583

• Study Protocol and Statistical Analysis Plan (PDF, 2020-06-19)

• Christopher Puccini, MD, Principal investigator, University of Utah