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Torsion is Tolerated in Arterial End to Venous Side Anastomoses in the Rat Model.

BACKGROUND
 End-to-side (ETS) anastomoses are necessary for many procedures in microvascular surgery, such as free flap transfers. In training courses that use the rat model, the arterial end to venous side (AEVS) anastomosis is a common training exercise for ETS anastomoses. Surgeons-in-training often inadvertently twist the artery when completing the AEVS anastomosis; however, in the clinical setting, torsion is a reported risk factor for ETS anastomosis failure. The purpose of this study was to determine if torsion in an AEVS anastomosis would have a negative effect on patency in the rat model, accurately simulating the clinical scenario.


METHODS
 All AEVS anastomoses were completed in 15 Sprague-Dawley rats divided into three torsion cohorts: 0, 90, and 180 degrees. Torsion was created in the AEVS anastomosis by mismatching the first two sutures placed between the free femoral artery end and the venotomy. Patency was verified at 0, 2, and 4 hours postoperation via the oxygenated-deoxygenated test and transit-time ultrasound blood flow measurements.


RESULTS
 All AEVS anastomoses were patent 0, 2, and 4 hours postoperation according to both the oxygenated-deoxygenated test and transit-time ultrasound blood flow measurements. For the average blood flow measurements at 4 hours postoperation, the proximal measurements for 0, 90, and 180 degrees were -34.3, -18.7, and -13.8 mL/min respectively, and the distal measurements were 4.48, 3.46, and 2.90 mL/min, respectively.


CONCLUSION
 Torsion of 180 degrees does not affect early AEVS anastomosis patency in the rat model. This contrasts with the clinical setting, where torsion is reported to cause ETS anastomosis failure. Since AEVS anastomosis torsion is often difficult to appreciate visually, we suggested that microvascular surgery training instructors include a method to both detect and prevent AEVS anastomosis torsion, such as by marking the free femoral artery end with a marking pen or suture before beginning the anastomosis.