Hemodynamic Principles in Free Tissue Transfer: Vascular Changes at the Anastomosis Site

Abstract

Purpose: Various factors such as blood velocity, turbulent flow,and intimal injury are the most basic elements in free tissue transfers. However, how blood flow is reestablished, maintained, and changed after vascular anastomosis has rarely been studied.Methods: A 54-year-old male sustained an unreplantable severe crushing injury to his right hand. The middle finger was transferred to the thumb as an ectopic replantation using an anastomosis between the radial and digital arteries. However, secondary reconstruction for the first web space defect was inevitable and an anteromedial thigh free flap procedure was performed 2 months later using the previously anastomosed vessels. During the procedures, we noted morphologic changes in the microvessels and tried to explain those phenomena by applying the principles of hemodynamics.Results: Due to the discrepancy in vascular size between the radial and digital arteries, the velocity of the blood flow in the post-anastomotic site, which was the digital artery, must have been increased by Poiseuille’s law. Supposing that the velocity through the post-anastomotic site of the digital artery was increased, the pressure exerted by that flow decreased, resulting in more shrinkage of the vessel lumen of the digital artery by Bernoulli’s principle. Pascal’s law could also be applied in confined spaces with a static flow; where there is a constant pressure, as the radius of the post-anastomotic digital artery diminishes, the tension within the digital artery’s wall also simultaneously decreases. By Laplace’s law, the post-anastomotic digital artery’s wall thickens as less tension is exerted on the wall.Conclusion: Understanding these simple flow mechanics will enable microsurgeons to better avoid the risk factors causing thrombosis, which is related to flap failure.

Supermicrosurgery with perforator‐to‐perforator anastomoses for lower limb reconstructions – A systematic review and meta‐analysis

“…Additionally, Badash et al (2018) discussed an alleged increased inherent risk of thrombosis in small‐caliber perforator thrombosis which ultimately leads to flap necrosis. This could be due to several reasons: a higher risk of caliber mismatch due to uneven lumens (Fensterer et al, 2014; Zhou et al, 2010), turbulent blood flow due to vessel wall irregularity leading to turbulence‐induced thrombogenicity (Doh et al, 2021; Krijgh et al, 2021), or vessel wall collapse due to low inner lumen pressures, since blood flow rate proportionally decreases with reduction in vessel diameter (Drzewiecki et al, 1997). Finally, another concern has been raised by Kim et al (2015), according to whom the use of perforator‐to‐perforator should be limited to small‐sized flaps, as a single low‐caliber vessel may not be adequate to perfuse across large flap areas.…”

Hand Reconstruction Using Anterolateral Thigh Free Flap by Terminal Perforator-to-Digital Artery Anastomosis: Retrospective Analysis

“…Moreover, such discrepancies can lead to unpredictable results owing to variables, such as turbulence and shearing forces. [3] Therefore, when an ALT free flap is applied with the digital artery as the recipient, it is suitably sized for anastomosis with the terminal perforator. (Figure 3.)…”

“…In cases with differences in diameter, factors, such as turbulence, can occur within the vessel owing to the viscosity of blood, increasing the risk of thrombosis. [3] In This article is protected by copyright. All rights reserved.…”

“…Therefore, it is important to select a suitable recipient vessel at an appropriate level and harvest perforators of appropriate length and diameter. [3] 1) If a larger vessel, such as the metacarpal artery or wrist vessel, is used as the recipient vessel, a larger perforator is required, and dissection up to the source vessel is necessary. (Figure 1,A) 2) In contrast, if the digital artery is used as the recipient vessel, a terminal perforator can be used without further dissection.…”

“…Therefore, it is important to select a suitable recipient vessel at an appropriate level and harvest perforators of appropriate length and diameter. 3 …”