Why can arteriovenous (AV) fistulas divert blood flow from distal tissues, potentially causing ischemia and contributing to edema through inflammatory responses?

From the Guidelines

Arteriovenous fistulas (AVFs) can steal blood flow from distal tissues, leading to ischemia and edema, due to the creation of a low-resistance pathway that diverts blood directly from the arterial to the venous system, bypassing the capillary network. This phenomenon, known as "steal syndrome," occurs because blood follows the path of least resistance, preferentially flowing through the fistula rather than continuing through smaller arteries to supply distal tissues 1. When tissues receive inadequate blood supply, they become ischemic, triggering inflammatory responses as cells release cytokines and other inflammatory mediators in response to oxygen deprivation. This inflammation increases vascular permeability, allowing fluid to leak from blood vessels into surrounding tissues. Additionally, the increased venous pressure caused by the fistula impairs normal venous return, further contributing to fluid accumulation.

The mechanisms underlying steal syndrome are complex and involve multiple factors, including the diversion of blood flow, reduced arterial supply, and increased venous pressure. According to the KDOQI guidelines, steal syndrome can lead to a range of signs and symptoms, from mild numbness to severe motor impairment or skin ulceration to gangrene necessitating major amputation 1. The creation of an AVF can also lead to changes in blood flow and pressure, which can contribute to the development of edema and other complications.

Some key points to consider when evaluating the risk of steal syndrome and edema in patients with AVFs include:

• The presence of a low-resistance pathway that diverts blood directly from the arterial to the venous system
• The potential for reduced arterial supply to distal tissues
• The increased venous pressure caused by the fistula
• The risk of inflammatory responses and increased vascular permeability
• The potential for edema formation in tissues distal to the arteriovenous fistula.

It is essential to carefully evaluate patients with AVFs for signs and symptoms of steal syndrome and edema, and to consider the potential risks and benefits of creating an AVF in patients with underlying vascular disease or other risk factors 1.

From the Research

Arteriovenous Fistulas and Blood Flow

• Arteriovenous fistulas (AVFs) can steal blood flow from distal tissues, potentially leading to ischemia and further contributing to edema through inflammatory responses 2, 3, 4, 5, 6.
• The creation of AVFs can lead to complications such as Hemodialysis Access-Induced Distal Ischemia (HAIDI) and high-flow AVFs, which can disrupt overall circulatory dynamics 2.
• HAIDI is characterized by ischemia in extremities due to reduced capillary perfusion, potentially leading to severe outcomes such as tissue necrosis and digital amputations 2.

Pathophysiological Basis of Steal Syndrome

• The pathophysiological basis of steal syndrome is a marked decrease or reversal of flow in the arterial segment distal to the AV fistula or AV graft, induced by the low resistance of the fistula outflow 4.
• Steal syndrome can manifest with either mild symptoms (coolness, paresthesia, and absence of distal pulses), or severe symptoms (rest pain, severe paresthesia, paralysis, cyanosis, and gangrene) immediately after construction of the AV access or later after its inception 4.

Diagnosis and Treatment of Steal Syndrome

• Diagnosis of steal syndrome is based on clinical manifestations, aided by the vascular laboratory and angiography 4, 6.
• Treatment of steal syndrome includes observation of developing symptoms in mild cases, balloon angioplasty for arterial stenosis, and surgical corrective procedures such as access ligation, banding, elongation, distal arterial ligation, and distal revascularization-interval ligation 3, 4, 6.
• Endovascular embolization using vascular plugs or coils can also be used to treat steal syndrome, particularly in cases where surgical intervention is not feasible 3, 5.