Everything about Arteriovenous Fistula totally explained
An
arteriovenous fistula is an abnormal connection or passageway between an
artery and a
vein. It may be
congenital, surgically created for
hemodialysis treatments, or acquired due to
pathologic process, such as
trauma or erosion of an arterial
aneurysm.
Vascular access for hemodialysis
Patients with
end stage renal failure are treated with
hemodialysis. In dialysis, blood is withdrawn from an artery or vein, purified, and returned to a vein. The volume of blood is too great for veins to handle, so a vein must be enlarged. An artery and vein, usually in the arm above or below the elbow, are sewn together, to create a
fistula, and arterial pressure eventually enlarges the vein. The enlarged vein can accommodate a
cannula or large needle.
Pathophysiology
When an arteriovenous fistula is formed involving a major artery like the
abdominal aorta, it can lead to a large decrease in
peripheral resistance. This lowered peripheral resistance causes the heart to increase
cardiac output in order to maintain proper blood flow to all tissues. The physical manifestations of this would be a relatively normal systolic
blood pressure with a decreased diastolic blood pressure resulting in a wide (large)
pulse pressure.
Normal blood flow in the brachial artery is 85 to 110 milliliters per minute (mL/min). After the creation of a fistula, the blood flow increases to 400 to 500 mL/min immediately, and 700 to 1,000 mL/min within 1 month. A bracheocephalic fistula above the elbow has a greater flow rate than a radiocephalic fistula at the wrist. Both the artery and the vein dilate and elongate in response to the greater blood flow and shear stress, but the vein dilates more and becomes "arterialized". In one study, the cephalic vein increased from 2.3 mm to 6.3 mm diameter after 2 months. When the vein is large enough to allow cannulation, the fistula is defined as "mature."
Treatment
Congenital fistulas, if small, usually don't need treatment. Acquired fistulas can be treated by
surgery.
Further Information
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