Proof-of-Concept Studies for Marker-Based Ultrasound Doppler Analysis of Microvascular Anastomoses in a Modified Large Animal Model.

Background Despite attempts to solve the problem of flap monitoring, assessing the patency of vascular anastomoses postoperatively remains challenging. In addition, experimental data suggest that near-total vessel occlusion is necessary to produce significant changes in clinical appearance or monitoring devices. We sought to develop an ultrasound-based system that would provide definitive data on anastomotic function. Methods A system was developed consisting of a resorbable marker made from poly-lactic-co-glycolic acid (PLGA) implanted during the time of surgery coupled with ultrasound software to detect the anastomotic site and perform Doppler flow analysis. Surgical procedures consisting of microvascular free tissue transfer or femoral vessel cutdown were performed followed by marker placement, closure, and ultrasound monitoring. Transient vascular occlusion was produced via vessel-loop constriction. Permanent thrombosis was induced via an Arduino-controlled system applying current to the vessel intima. Results Four surgeries (one femoral vessel cutdown and three microvascular tissue transfer) were successfully performed in Yorkshire swine. The markers were readily visualized under ultrasound and provided a bounding area for Doppler analysis as well as orientation guidance. Transient spasm and partial occlusion were detected based on changes in Doppler data, while complete occlusion was evident as the total loss of color Doppler. Conclusion In this preliminary report, we have conceptualized and developed a novel system that enables the real-time visualization of vascular pedicle flow at the bedside using Doppler ultrasound and a surgically implanted marker. In a large animal model, use of the system allowed identification of the anastomosis, flow analysis, and real-time detection of flow loss.