Chronic kidney disease often requires hemodialysis, a treatment that filters waste and excess fluid from the blood. Effective hemodialysis requires a robust, long-term access point to the patient’s bloodstream. This specialized access, known as an arteriovenous (AV) fistula, is the preferred option. The AV fistula provides a durable connection that sustains the high flow rates required by the dialysis machine.
Defining the Arteriovenous Fistula
An arteriovenous fistula is a surgically created connection between an artery and a vein, usually established in the arm or wrist. Normally, arteries carry high-pressure blood away from the heart, and veins return low-pressure blood. The fistula bypasses the normal capillary bed, joining the artery and vein directly. This union forces high-pressure arterial blood flow into the low-pressure vein, a process called arterialization.
This physiological change causes the vein walls to strengthen and remodel over time. The increased pressure stimulates the vein to dilate and thicken. This structural transformation prepares the vessel to endure the repeated needle insertions required for hemodialysis treatments. The resulting vessel is strong enough to handle the volume and trauma of regular access.
Surgical Creation and Maturation
A vascular surgeon creates an AV fistula by connecting a native vein, such as the cephalic or basilic vein, to an adjacent artery. The procedure is usually performed on the non-dominant arm in an outpatient setting under local anesthesia. Surgeons aim to create the anastomosis, or surgical junction, as far down the arm as possible to preserve proximal vessels for future access.
After surgery, the fistula requires a dedicated period of development called maturation before it can be used for dialysis. This biological process typically takes six to twelve weeks. During maturation, the vein expands and thickens sufficiently to accommodate the large needles used during treatment sessions. Physicians often use the “Rule of 6s” to confirm readiness: a diameter of at least six millimeters, a blood flow of at least 600 milliliters per minute, and a straight segment of six centimeters close to the skin.
Function and Utility in Hemodialysis
The mature AV fistula provides the high-flow access necessary for efficient hemodialysis. The dialysis machine requires a rapid flow of blood to effectively filter waste products and excess fluids. The arterialized fistula consistently supplies this required flow rate, which smaller, native veins cannot sustain.
During a dialysis session, two specialized needles are inserted into the fistula. One needle draws blood to send it to the dialyzer, the filtering component of the machine. The second needle returns the cleaned blood back into the patient’s circulation. Compared to other types of vascular access, the fistula has a lower risk of infection and thrombosis, or clotting.
Essential Care and Monitoring
Daily monitoring of the AV fistula is important for maintaining its long-term function. Patients must regularly check for the “thrill,” a distinct buzzing or vibratory sensation felt over the access site. The thrill indicates that the high-pressure blood flow is patent and flowing correctly. A loss or weakening of the thrill suggests a clot or narrowing may be forming and requires immediate medical evaluation.
A “bruit” can also be heard by listening over the fistula with a stethoscope. This whooshing sound is the auditory equivalent of the thrill and helps assess blood flow. Patients must take protective measures to avoid injury or compression to the access arm, such as avoiding tight clothing, jewelry, or sleeping on the arm.
Protecting the Access Arm
The fistula arm should never be used for blood pressure readings, blood draws, or intravenous insertions, as these can damage the vessel or cause a clot. Patients should watch the access site daily for signs of infection, such as redness, warmth, swelling, or drainage. Concerning symptoms that warrant immediate medical attention include pain, numbness, or tingling in the hand. These symptoms can signal “steal syndrome,” a condition where the fistula diverts too much blood away from the hand and fingers.