A fistula is a surgically created connection between an artery and a vein, most commonly used to provide reliable access to the bloodstream for hemodialysis. People with kidney failure need dialysis several times a week, and a fistula gives healthcare providers a durable, low-risk entry point to filter the blood. While the word “fistula” can also refer to abnormal connections that form from injury or disease, the most common reason someone has a fistula intentionally created is to support long-term dialysis treatment.
How a Fistula Works for Dialysis
During hemodialysis, blood needs to be drawn out of the body, run through a machine that filters out waste and excess fluid, and then returned. This requires a access point that can handle high blood flow repeatedly, sometimes three or more times per week, for years. A standard vein is too small and fragile for that kind of use.
A fistula solves this by connecting an artery directly to a vein, usually in the arm. Arterial blood flows into the vein under higher pressure than the vein normally handles, which causes the vein to enlarge and its walls to thicken over time. This “matured” vein becomes strong enough to tolerate repeated needle insertions. During each dialysis session, two needles are placed into the enlarged vein: one draws blood out to the machine, and the other returns the cleaned blood to the body.
Why Fistulas Are Preferred Over Other Options
Three types of vascular access exist for dialysis: fistulas, grafts (a synthetic tube connecting artery to vein), and central venous catheters (tubes placed in a large vein in the chest or neck). Clinical guidelines rank fistulas as the first choice, grafts second, and catheters last.
The main advantage is durability. Fistulas use your own tissue rather than foreign material, which dramatically lowers infection risk. In a meta-analysis comparing fistulas to grafts in elderly patients, grafts carried nearly ten times the infection rate. Patients with grafts also had significantly worse overall survival, with a 38% higher risk of death compared to those with fistulas. Because there’s no synthetic material for bacteria to colonize, fistulas simply hold up better over time. Catheters carry the highest infection risk of all three and are generally reserved for urgent or temporary situations.
Where a Fistula Is Placed
Surgeons typically create fistulas in the non-dominant arm, starting as far from the shoulder as possible to preserve future access sites if needed. The three most common types are:
- Radiocephalic (forearm): Connects the radial artery to a vein near the wrist. This is often the first choice because it has the lowest rate of steal syndrome (about 1%), a complication where the hand doesn’t get enough blood flow. The trade-off is a higher chance the fistula won’t mature properly.
- Brachiocephalic (upper arm): Connects the brachial artery to a vein just above the elbow. These mature more reliably and last longer, but steal syndrome rates are higher (5 to 20%), and placing one here rules out creating a forearm fistula later.
- Transposed basilic vein (upper arm): Uses a deeper vein that must be surgically repositioned closer to the skin surface. This is typically a backup option when the first two aren’t feasible.
The Maturation Period
A fistula can’t be used immediately after surgery. The vein needs time to enlarge and strengthen under the increased blood flow. This maturation process typically takes 4 to 6 weeks, though the full range can be anywhere from 1 to 4 months depending on the individual. During this waiting period, patients who already need dialysis will use a catheter or other temporary access.
Not every fistula matures successfully. The most common reason for failure is narrowing near the surgical connection point, which restricts blood flow and prevents the vein from developing properly. If maturation stalls, a procedure to widen the narrowed area can sometimes salvage the fistula.
What Dialysis Feels Like Through a Fistula
Each dialysis session involves two needle sticks into the matured vein. Several techniques exist for placing these needles, and the approach can affect comfort. In the “rope ladder” method, new puncture sites are chosen each session, spreading the wear across the length of the vein. The “buttonhole” technique uses the same sites every time, creating small tunnels that make insertion easier and less painful. This method is particularly common for people who do dialysis at home.
Over time, repeated punctures destroy nerve fibers in the area, which naturally reduces pain during needle insertion. However, this comes with a trade-off: the repeated trauma to the same tissue can contribute to bulging (aneurysms) and other complications over the long term. Some practitioners insert needles bevel-down to reduce discomfort and lower the risk of puncturing through the back wall of the vein.
How to Tell if a Fistula Is Working
A healthy fistula produces two telltale signs. The first is a “thrill,” a gentle vibration you can feel by placing your fingers lightly over the fistula site. The second is a “bruit,” a low-pitched, continuous whooshing sound you can hear with a stethoscope or sometimes by pressing your ear near the access site. The thrill should be strongest at the point where the artery and vein connect and detectable along the length of the outflow vein.
Patients are typically taught to check for the thrill daily, especially after episodes of low blood pressure, which can cause clotting. If the vibration or sound disappears, that’s a sign of a potential blockage that needs prompt attention. Other warning signs include persistent arm swelling, visible new veins branching across the skin surface (collateral veins), and prolonged bleeding after needle removal.
Complications to Be Aware Of
The most common complications are narrowing (stenosis) and blood clots (thrombosis). Narrowing gradually reduces blood flow and, if untreated, can lead to clotting that blocks the fistula entirely. These are typically caught through changes in the thrill or bruit, or when dialysis sessions become less efficient.
Steal syndrome occurs in up to 6% of patients. The fistula diverts so much blood that the hand and fingers downstream don’t receive enough. Normally the body compensates by increasing overall blood flow to the arm, but when that mechanism fails, the affected hand can feel cold, numb, or painful. Upper arm fistulas carry a higher risk of this than forearm fistulas.
In rare cases, a very high-flow fistula can strain the heart. The direct artery-to-vein connection lowers resistance in the circulatory system, which forces the heart to pump harder to maintain blood pressure. In a study of 120 patients with high-output heart failure, 23% had some form of arteriovenous shunt contributing to the problem. This is more likely with older, well-established fistulas that have grown to carry very high volumes of blood.
Fistulas That Aren’t Surgically Created
Outside of dialysis, the word “fistula” refers to any abnormal tunnel-like connection between two body parts that shouldn’t be connected. These are not created on purpose and typically result from injury, infection, surgery complications, or prolonged labor during childbirth. Vaginal fistulas, for instance, can form between the vagina and the bladder, rectum, or intestines, causing urinary or fecal leakage. Perianal fistulas form near the anus, often as a complication of Crohn’s disease or an abscess. These types of fistulas are medical problems that require treatment, not tools with a deliberate function like a dialysis fistula.