54. Implementation of a Risk-stratified Anticoagulation Protocol Increases Free Flap Success in Thrombophilic Patients With Chronic Lower Extremity Wounds

Purpose: A hypercoagulable state is one of the most challenging preoperative conditions that reconstructive microsurgeons face. Optimal perioperative thromboprophylaxis is crucial to avoid flap thrombosis and to achieve high rates of microsurgical success in patients undergoing lower extremity (LE) free tissue transfer (FTT). At our institution, implementation of a risk-stratified anticoagulation (AC) protocol preliminarily showed a reduction in postoperative thrombotic events and flap loss. After six years of experience with this protocol, we present an updated analysis of surgical outcomes and the utility of risk-stratified AC in thrombophilic patients who underwent FTT reconstruction for chronic LE wounds. Methods: We conducted a retrospective review of patients who underwent FTT to the LE at our institution from January 2012 to August 2021. Patients were preoperatively assessed for hypercoagulability based on history and a screening panel. Our risk-stratification AC protocol was implemented in July 2015. Low-risk (<3 hypercoagulable traits) and moderate-risk (>3 hypercoagulable traits or history of venous thromboembolism) patients were anticoagulated with subcutaneous heparin (SQH). Any intraoperative risk factor (thrombosis, anastomotic revision, presence of calcified vessels) upstaged patients to high microvascular risk. High-risk patients received heparin infusion titrated to a goal PTT of 50-70 seconds. Prior to July 2015, non-stratified patients were treated with SQH for uncomplicated microvascular anastomoses, while patients with microvascular compromise were converted to a low-dose heparin infusion (500 units/hour). Patients were divided into two cohorts (non-stratified and risk-stratified) based on the date of FTT reconstruction. Primary outcomes included rates of postoperative complications, flap salvage, and flap success. Results: A total of 219 hypercoagulable patients who underwent FTT to LE were treated with either non-stratified (n=26) or risk-stratified (n=193) thromboprophylaxis. Overall flap success rate was 96.8% (n=212). Lower rates of flap loss (1.6% vs. 15.4%, p=0.004) were observed among risk-stratified patients, which paralleled a significant reduction in the prevalence of postoperative thrombotic events (2.6% vs. 15.4%, p=0.013). Flap salvage, in the setting of postoperative thrombosis, was accomplished in 80% of cases in the risk-stratified cohort compared to 0% in the non-stratified group (p=0.048). Bleeding complications and transfusion requirements were similar among the two cohorts. On multivariate analysis, intraoperative anastomotic revision (OR: 3.10; p<0.001) and non-risk stratification (OR: 11.2; p=0.001) were independently associated with flap failure. Non-risk stratification for thromboprophylaxis was an independent predictor of perioperative microvascular thrombosis (OR: 3.71; p=0.041). Conclusion: Hypercoagulability can significantly impact microsurgical outcomes. Preoperative identification of hypercoagulable traits and intraoperative risk factors can successfully guide perioperative thromboprophylaxis. Implementation of a risk-stratified AC protocol at our institution has contributed to significant improvements in flap success without creating an increased need for blood transfusion.