page_title: Vascular access
section_title: AV fistula
hierarchical_section_title: Vascular access / AV fistula
caption_attribution_description: English: Hemodialysis. See a full animation of this medical topic.
context_page_description: Vascular access refers to a rapid, direct method of introducing or removing devices or chemicals from the bloodstream. In hemodialysis, vascular access is used to remove the patient's blood so that it can be filtered through the dialyzer. Three primary methods are used to gain access to the blood: an intravenous catheter, an arteriovenous fistula or a synthetic graft. In the latter two, needles are used to puncture the graft or fistula each time dialysis is performed.
  The type of vascular access created for patients on hemodialysis is influenced by factors such as the expected time course of a patient's kidney failure and the condition of his or her vasculature. Patients may have multiple accesses, usually because an AV fistula or graft is maturing and a catheter is still being used. The creation of all these three major types of vascular accesses requires surgery.
context_section_description: AV (arteriovenous) fistulas are recognized as the preferred access method. To create a fistula, a vascular surgeon joins an artery and a vein together through anastomosis. Since this bypasses the capillaries, blood flows rapidly through the fistula. One can feel this by placing one's finger over a mature fistula. This is called feeling for "thrill" and produces a distinct 'buzzing' feeling over the fistula. One can also listen through a stethoscope for the sound of the blood "whooshing" through the fistula, a sound called bruit.
  Fistulas are usually created in the nondominant arm and may be situated on the hand (the 'snuffbox' fistula'), the forearm (usually a radiocephalic fistula, or so-called Brescia-Cimino fistula, in which the radial artery is anastomosed to the cephalic vein), or the elbow (usually a brachiocephalic fistula, where the brachial artery is anastomosed to the cephalic vein). Though less common, fistulas can also be created in the groin, though the creation process differs. Placement in the groin is usually done when options in the arm and hands are not available due to anatomy or the failure of fistulas previously created in the arms/hands. A fistula will take a number of weeks to mature, on average perhaps 4–6 weeks.
  During treatment, two needles are inserted into the vein, one to draw blood and one to return it. The orientation of the needles takes the normal flow of the blood into account. The "arterial" needle draws blood from the "upstream" location while the "venous" needle returns blood "downstream". This sequence prevents partial recycling of the same blood through the dialysis machine, which would lead to less effective treatment.
  The advantages of the AV fistula use are lower infection rates, because no foreign material is involved in their formation, higher blood flow rates (which translates to more effective dialysis), and a lower incidence of thrombosis. The complications are fewer than with other access methods. If a fistula has a very high blood flow and the vasculature that supplies the rest of the limb is poor, a steal syndrome can occur, where blood entering the limb is drawn into the fistula and returned to the general circulation without entering the limb's capillaries. This results in cold extremities of that limb, cramping pains, and, if severe, tissue damage. One long-term complication of an AV fistula can be the development of an aneurysm, a bulging in the wall of the vein where it is weakened by the repeated insertion of needles over time. To a large extent the risk of developing an aneurysm can be reduced by carefully rotating needle sites over the entire fistula, or using the "buttonhole" (constant site) technique. Aneurysms may necessitate corrective surgery and may shorten the useful life of a fistula. Fistulas can also become blocked due to blood clotting or infected if sterile precautions are not followed during needle insertion at the start of dialysis. Because of the high volume of blood flowing through the fistula, excessive bleeding can also occur. This is most common soon after a dialysis treatment. Pressure must be applied to the needle holes to induce clotting. If that pressure is removed prematurely or a patient engages in physical activity too soon after dialysis, the needle holes can open up.
  To prevent damage to the fistula and aneurysm or pseudoaneurysm formation, it is recommended that the needle be inserted at different points in a rotating fashion. Another approach is to cannulate the fistula with a blunted needle, in exactly the same place. This is called a 'buttonhole' approach. Often two or three buttonhole places are available on a given fistula. This also can prolong fistula life and help prevent damage to the fistula.
  A recent study that was published in The American Journal of Pathology, provides information about the mechanisms underlying failure of the most common type of hemodialysis vascular access, the arteriovenous fistula. In spite of AV Fistula being one of the most preferred methods of Vascular access, the researchers observed that, up to 60
caption: Illustration depicting AV fistula during hemodialysis
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