A fistula is an abnormal connection that forms between two structures or spaces within the body. In a medical context, the term most commonly refers to the arteriovenous (AV) fistula created for life-sustaining treatment. This surgically created connection links an artery and a vein, providing the preferred vascular access for accessing the bloodstream during hemodialysis for individuals with kidney failure.
Anatomy and Types of Fistulas
An arteriovenous fistula joins a high-pressure artery directly to a low-pressure vein, usually in the arm or wrist. This direct surgical connection, known as an anastomosis, bypasses the capillary bed that normally separates the two vessel types. While pathological AV fistulas can occur naturally due to trauma or disease, the type used for dialysis is intentionally created to handle the demands of blood filtration. Common locations for these accesses include the wrist (radiocephalic) or the elbow (brachiocephalic).
The Role of Fistulas in Dialysis Access
The AV fistula is the gold standard for vascular access in patients receiving long-term hemodialysis. Hemodialysis requires drawing and returning blood at a high flow rate, often between 300 to 500 milliliters per minute, which a normal, thin-walled vein cannot sustain. By connecting the artery and vein, the fistula forces the vein to adapt to the increased volume and pressure of arterial blood flow. This process, known as venous arterialization, causes the vein to thicken and enlarge, making it strong enough for repeated needle insertions.
Compared to other access methods, such as synthetic grafts or central venous catheters, the AV fistula offers significant advantages. Fistulas last longer, utilize the patient’s native tissue, and have a lower risk of infection and blood clots, which translates to fewer hospitalizations and interventions over time.
Surgical Creation and Maturation
Creating an AV fistula is typically a minor outpatient procedure, often using local anesthesia. The surgeon performs the anastomosis by stitching the wall of an artery to the wall of an adjacent vein, establishing the new circulatory pathway.
Following surgery, the fistula requires a period of maturation, which can take anywhere from six weeks to several months. During this time, the increased pressure and flow from the artery stimulate the vein’s wall to thicken and increase in diameter. Patients are often encouraged to perform simple exercises, such as squeezing a soft ball, to promote blood flow and encourage the vein to enlarge. A mature fistula must meet specific criteria regarding size, depth, and blood flow rate to allow for successful and repeated cannulation with dialysis needles.
Recognizing and Addressing Complications
Even after successful maturation, an AV fistula requires careful monitoring to ensure proper function. The most common complications include stenosis (vessel narrowing) and thrombosis (a blood clot). Patients must check their fistula daily by feeling for the “thrill,” a distinct buzzing sensation created by the rapid blood flow. A diminished or absent thrill indicates a blockage and requires immediate medical attention.
Other complications include infection (redness, swelling, or warmth) and “steal syndrome.” Steal syndrome occurs when the fistula diverts too much arterial blood away from the hand, causing coldness, numbness, or pain. Recognizing these signs early and contacting the care team promptly can prevent the loss of the access.