Affiliations: Department of Trauma and Plastic Surgery, University of Regensburg, Regensburg, Germany | Department of Vascular Surgery, University of Regensburg, Regensburg, Germany | Department of Diagnostic Radiology, University of Regensburg, Regensburg, Germany
Note: [] Corresponding author: Lukas Prantl, MD, PhD, Diplomate of EBOPRAS, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany. Tel.: +49 941 9446947; E-mail: lukas.prantl@klinik.uni-regensburg.de.
Abstract: Purpose: The aim of the prospective study was to evaluate the macro- and microcirculation in the center and periphery of free flaps with high resolution vascular ultrasound. Material: Fifteen patients with free parascapular flaps after lower limb trauma were examined six months postoperative. All ultrasound investigations were performed by one experienced examiner with a multi-frequency linear transducer (5–9 MHz, Logiq 9, GE). Flow evaluation was angle-optimized using digital image technology with the color coded Doppler sonography (CCDS) with measurement of the peak systolic, peak diastolic flow velocities and the resistance index (RI). Contrast harmonic imaging (CHI) with time intensity curve (TIC) analysis was used for quantitative evaluation of the tissue perfusion. Through a peripheral cubital cannula, a first bolus injection was made of 2.4 ml Sonovue® to evaluate the perfusion near the flap center and the distal part of the flap. Results: The combined analysis of all 15 patients showed in the center and in the periphery of the flap a significant increase (p<0.01; Wilcoxon signed rank test) of the perfusion (relative units = RUs) in the period of 90–120 s after contrast medium application (center: baseline perfusion 2.23±0.31 RUs to 5.25±0.90 RUs after contrast medium; periphery: baseline perfusion 3.07±0.44 RUs to 5.80±0.57 RUs after contrast medium). The separate analysis of the non-bypass group (n=9) and bypass group (n=6) showed a clearly higher central flap perfusion after contrast medium application for the bypass group. The combined analysis of all patients showed RI-values amounting to 0.79±0.03. The RI-values of the bypass group were significantly higher than RI-values of the non-bypass group (p<0.05; t-test; p<0.05; Mann–Whitney rank sum test). Conclusion: The high-resolution ultrasound represents an ideal method for detection of the flow and patency of the bypass and the small vessels of the free flap. The patency of microvascular anastomosis as well as the perfusion and microcirculation in different flap territories and tissue layers can be investigated using dynamic contrast-enhanced ultrasound with subtraction modalities.
