For individuals with kidney failure requiring frequent blood filtration, a reliable access point to the bloodstream is paramount for hemodialysis. Standard veins in the body cannot withstand the repeated needle insertions or provide the high volume of blood flow required to efficiently filter toxins and excess fluid. This challenge is addressed through the creation of a specialized, long-term connection known as a vascular access. The preferred and most durable type of vascular access is the arteriovenous (AV) fistula, which is created surgically to provide a robust, long-lasting site for treatment. Establishing this access point well in advance of starting dialysis helps ensure continuous, effective therapy.
Defining the Arteriovenous Fistula
An arteriovenous fistula is a surgically created connection between two different types of blood vessels: an artery and a vein. Arteries carry high-pressure, oxygen-rich blood away from the heart, while veins are lower-pressure vessels that return blood back to the heart. The fistula directly joins an artery to a neighboring vein, typically in the arm or wrist.
This direct surgical connection, called an anastomosis, bypasses the usual network of capillaries. As a result, the high-pressure, high-flow blood from the artery is suddenly routed into the lower-pressure vein. This increased blood flow and pressure forces the vein to adapt and enlarge, which is what makes it suitable for dialysis. The resulting structure is stronger, provides the necessary high blood flow, and is less prone to the infections and clotting seen with other access types.
Creating the Fistula
Creating a fistula is a minor surgical procedure performed by a vascular specialist, often on an outpatient basis, allowing the patient to return home the same day. Surgeons typically use local or regional anesthesia to numb the arm.
Before the procedure, the surgeon assesses the patient’s vessels using ultrasound to map the best artery and vein. The location is generally chosen in the non-dominant arm, ranging from the wrist (radiocephalic fistula) to the forearm or elbow (brachiocephalic fistula). A small incision is made, and the artery and vein are carefully sewn together, redirecting arterial blood flow into the chosen vein.
Maturation and Use for Dialysis
Following surgery, the fistula must undergo a period of development known as maturation before it can be used for dialysis. The high-pressure arterial blood flow causes the vein walls to thicken and enlarge (arterialization and dilation). This transformation makes the vein robust enough to withstand the repeated needle insertions required for hemodialysis.
The maturation period is variable but typically takes between two to three months, though it can sometimes take longer. This waiting time is essential because attempting to use an immature fistula risks permanent failure due to vessel collapse or damage. Successful maturation is often defined by the “Rule of Sixes,” which suggests the vein should have a diameter of at least 6 millimeters, be no deeper than 6 millimeters beneath the skin, and have a blood flow rate of at least 600 milliliters per minute.
Once fully mature, two specialized needles are inserted into the enlarged vein for each dialysis session. One needle draws blood out to the dialysis machine for filtering, and the second returns the cleaned blood back into the patient’s body. The high flow rate ensures the dialysis machine can efficiently cleanse the blood, often filtering about a pint of blood every minute.
Daily Care and Monitoring
Proper daily care is necessary to ensure the fistula remains functional for years of dialysis treatment. Patients must protect the access arm by avoiding any activity that could restrict blood flow or damage the vessel, including wearing tight jewelry or clothing, carrying heavy objects, or sleeping with the arm in a compressed position.
It is strictly advised that no blood pressure measurements, blood draws, or intravenous injections be performed on the fistula arm. A fundamental aspect of daily monitoring is checking the “thrill,” which is the distinct purring or buzzing vibration felt when lightly touching the fistula. The presence of a strong thrill indicates blood is flowing correctly, while its absence or a noticeable decrease can signal a potential blockage.
Patients should also monitor for warning signs requiring immediate medical attention, such as swelling, unusual pain, or infection (redness, warmth, or discharge). Another sign of proper function is the “bruit,” a continuous, low-pitched swooshing sound heard over the fistula with a stethoscope. Promptly reporting any changes to the healthcare team ensures the longevity of the fistula.