Blood clots that form in the extremities (deep venous thrombosis) and lungs (pulmonary embolus) are feared complications of reconstructive surgery. One in ten patients with symptomatic pulmonary embolus will be dead in 60 minutes. Patients with deep venous thrombosis can develop the post-thrombotic syndrome, known to be a major driver of poor quality of life. These phenomena, broadly known as venous thromboembolism (VTE), have substantial downstream ramifications, and the US Surgeon General and the American Society of Plastic Surgeons (ASPS), among others, have underscored the importance of VTE prevention in surgical patients. Reconstructive surgery, most commonly performed to fix traumatic injuries or defects after cancer excision, often involves borrowing tissue from adjacent or distant areas on the body; reconstructive surgery patients can routinely have surgical injury involving 20% or more of their total body surface area. Injury and resultant inflammation are known to increase metabolism of certain drugs, including those used to prevent VTE after surgery.

Enoxaparin is a blood-thinning medication that decreases likelihood of blood clot formation. Previous research has shown that reconstructive surgery patients who are given enoxaparin after surgery are less likely to develop VTE. However, despite receiving of a standard dose of enoxaparin, many patients still develop this life-threatening complication. The investigators believe that patients metabolize enoxaparin differently based on the degree of surgical injury created during reconstruction, and seek to critically examine enoxaparin metabolism in reconstructive surgery patients. The proposed research will evaluate how enoxaparin affects the blood based on standard, ASPS-recommended dosing after reconstructive surgeries; the investigators will also examine whether the extent of surgical injury alters metabolism as well. Enoxaparin effectiveness will be tracked using anti-Factor Xa (aFXa) levels. If subtherapeutic aFXa levels are observed, the study will also design, implement and test a clinical enoxaparin dose-adjustment protocol to achieve appropriate post-operative aFXa levels. Further research based on these data will examine reduction in VTE risk when aFXa-driven enoxaparin dosing is used.

The ultimate goal of the investigators research is to better understand the interplay between enoxaparin dosing, degree of surgical injury, and blood clots after major reconstructive surgery. Ultimately, this research will expand medicine's understanding of why post-operative VTE occurs, will allow the investigators to individualize a patient's VTE prophylaxis strategy based on their unique characteristics, and will further improve patient safety after reconstructive surgery.

Inclusion criteria:

• Adult patients having plastic and reconstructive surgery who are placed on twice daily enoxaparin prophylaxis after surgery.

Exclusion criteria:

• Contraindication to use of enoxaparin.
• Intracranial bleeding/stroke, hematoma or bleeding disorder.
• Known heparin-induced thrombocytopenia
• Creatinine clearance ≤30mL/min
• Serum creatinine >1.6mg/dL
• Epidural anesthesia.

Deidentified data will be shared.

9/4/18

American Society of Plastic Surgeons