Mechanisms and Management of Graft In- and Out-flow in Liver Transplantation: A Narrative Review of the Literature and Guide for Interventional Management.

Background And Aims: Management of the dual vascular supply of liver grafts in liver transplantation (LT) is increasingly recognized as crucial to achieving adequate graft function. We aim to review how the relationship between graft in-flow and out-flow affects graft function, and how surgeons can manage graft function within the context of liver hemodynamic autoregulation. This includes mechanisms of such autoregulation including the hepatic artery buffer response (HABR), and the impact of porto-systemic circulatory changes on graft inflow.

Methods & Results (review): This study represents a narrative review of the literature along with the editorial input/practices of the authors. A complex mechanistic understanding can guide surgeons in the management of common and even un-common vascular conditions after transplantation. Portal hyperperfusion is the most common, usually resulting from decreased intrahepatic adenosine and arterial vasoconstriction via the HABR. Such a concern is now recognized as the treatment of Small-for-Size Syndrome, and thus management of vascular in- and out-flow is also critical to the use of small liver grafts to preserve donor safety. Portal inflow modulation (PIM) using splanchnic vasodilators, splenic embolization, or splenectomy are all recognized treatments for hyperperfusion. However, the management of portal hypo-perfusion is less well described, with only isolated case reports describing the augmentation of portal venous in-flow. Finally, the impact of graft out-flow is reviewed, with a focus on how out-flow can improve graft utility in living donor liver transplantation.

Conclusions: Overall, an understanding of complex hepatic vascular regulation is essential to optimizing liver graft function in transplantation. This review may help surgeons as they continue to strive for improved access to transplantation across the world.