The hypercoagulable state in COVID-19 and implications for free flap surgery in the lower limb: A retrospective multi-centre study.

Aims: Hypercoagulability in severe COVID-19 infection and COVID-19 Vaccine-Induced Thrombotic Thrombocytopaenia have been widely documented. Most evidence pertains to macrovascular thrombosis. Little is known about the impact of previous (including mild or asymptomatic) COVID-19 infection or vaccination on microvascular thrombosis in free tissue transfer. This study compared the rate of thrombotic complications in lower limb free flap patients in the pre- and post-COVID era.

Methods: This study retrospectively collected data for patients who underwent lower limb free flap surgery for two 6-month periods at three major trauma centres. Eligible patients included adults with a minimum follow-up of 90 days. Modified Poisson regressions were used to compare the complication rates between cohorts who had and had not had previous COVID-19 infection, and between those who had and had not had previous COVID-19 vaccination.

Results: Complete data was collected for 198 free flaps. Two of ten patients who had a COVID-19 infection prior to surgery suffered a microvascular complication compared to 16 of 188 patients who had never had a COVID-19 infection (8.5%). Similarly, 12% of vaccinated patients experienced microvascular complications compared to 7% of unvaccinated patients.

Conclusions: Previous COVID-19 infection and/or vaccination do not appear to have a statistically significant impact on the development of microvascular complications in the context of lower limb free flap surgery, despite the well-documented impact on macrovascular complications, and additional thromboprophylaxis is unlikely to be necessary. Surgeons should continue to be mindful of the impact of serious systemic infection on thromboembolic disease when planning major surgery.