Objective
Free flaps had long been used for complicated reconstruction with good outcomes. The improvement of medical care and instruments had largely improved the outcome of free flap reconstruction.
The success of microsurgery depends on not only adequate pre-operation planning but also the surgeon technique and vessel quality. Previous studies had published the successful rate of free flap reconstruction was around 70-95%. The possible reasons of flap failure were mainly vascular events during the first three days, no matter arterial occlusion, venous thrombosis or both. The following reasons in the next days during the first week may be caused by possible hematoma, seroma or infection.
Some studies had prescribed using dextran for post-operative treatment in microvascular free flap reconstruction. However, no strong evidence could provide to decrease vascular events or flap failure rate. What’s more, may increase complication rate such as hematoma formation.
Therefore, in this study, we’d like to review the free flap transfer cases in our medical center during the past 5 years, whether the use of dextran influence the successful rate of free flap reconstruction.

Material and Methods
All patients in this study received free flap transfer under the reasons of malignancy, trauma, infection or trans-gender. Patients who were older than 18 years, received free flap reconstruction at our hospital, and had follow-up over 6 months were enrolled in the study. Exclusion criteria included incomplete medical record, convert to local flap reconstruction, microsurgery with lymphaticovenous anastomosis or follow-up time less than 6 months.

Results
Total of 668 patients received microsurgery at our hospital between 2016 to 2020. After exclusion, of which 30 patients were lymphedema related, having lymphaticovenous anastomosis instead of free tissue transfer as treatment. Also, 3 patients changed their reconstruction plan to local flap reconstruction during operation due to no adequate recipient vessel could be approached. 13 patients had incomplete medical record or missing data for analysis. Finally, total of 622 patients with 638 flaps were identified and enrolled in our study.
In our study, total 101 flaps received salvage surgery, in which 80 flaps had total or partial failure that need another soft tissue transfer or local flap reconstruction, in which, 71 flaps showed vascular event with arterial occlusion, venous thrombosis or mixed cause. 30 flaps showed negative finding with only hematoma accumulation or pedicle kinking. Further statistical analysis was performed between the flap failure and success groups to identify possible risk factor for flap failure.

Conclusion
In this study, dextran use didn’t interfere flap successful rate. The main independent risk factor is the number of flap perforators. However, further matched cohort study may try to decrease group difference and identify the possible risk factor and benefit of dextran.

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