If your dialysis fistula stops working, contact your dialysis care team or nephrologist right away. A fistula that loses its blood flow is a time-sensitive problem, not a wait-and-see situation. The sooner you get evaluated, the better the chances of saving the fistula and avoiding a temporary catheter for your dialysis treatments.
How to Tell Your Fistula Isn’t Working
A healthy fistula has two reliable signs of good blood flow. The first is a “thrill,” a steady vibration you can feel when you place your fingers over the fistula site. The second is a “bruit,” a whooshing or humming sound you can hear with a stethoscope or sometimes by holding your ear close to the site. Your dialysis team likely taught you to check for the thrill regularly, and that daily habit is your best early warning system.
If the thrill feels weaker than usual, disappears entirely, or the area around your fistula becomes swollen, painful, or looks different, those are signs that blood flow has been disrupted. A fistula that feels firm or hard to the touch, rather than soft and compressible, may have developed a clot. Some people also notice that their arm on the fistula side feels cold, numb, or tingly. Any of these changes warrant an immediate call to your care team.
Why Fistulas Stop Working
The most common reason is narrowing of the vein, called stenosis. Over time, the inner wall of the vein can thicken and gradually choke off blood flow. Vein narrowing is the primary cause of fistula clotting. It can happen near the point where the artery and vein were surgically joined, and this specific type of narrowing develops in roughly 50% of new fistulas within the first four to six weeks after creation.
When narrowing goes undetected, it typically leads to a blood clot (thrombosis) that blocks the fistula entirely. Early clotting, soon after a fistula is created, usually stems from problems with blood flowing into the fistula. Late clotting, months or years down the line, tends to result from a blockage on the outflow side, where blood is trying to leave the fistula and return to the heart. Low blood pressure, dehydration, and excessive pressure on the fistula arm (sleeping on it, wearing tight clothing, or having blood pressure taken on that arm) can also contribute.
Who to Call and How Quickly
Call your dialysis center or nephrologist as soon as you suspect a problem. If you can’t reach them and your next dialysis session isn’t imminent, call the on-call provider at your nephrology practice. This is not typically a 911 emergency, but it is urgent. A clotted fistula that sits untreated for days becomes harder to salvage.
Your care team will likely arrange for you to be seen within hours, not days. They need to determine whether the fistula still has any flow, whether a clot has formed, and whether the underlying cause is something they can fix. If your next dialysis session is coming up soon and your fistula isn’t functional, you’ll need an alternative way to dialyze, which is another reason speed matters.
Tests Used to Evaluate the Problem
The first-line test is a duplex ultrasound, which uses sound waves to measure how fast blood is moving through the fistula. It’s painless, noninvasive, and gives your team a clear picture of whether there’s narrowing, a clot, or another structural issue. This is the most common and effective way to check a fistula in the arm or leg.
If the ultrasound shows a problem that needs a closer look, your team may order a CT angiogram, which uses contrast dye injected through an IV to create detailed images of the blood vessels. In some cases, a fistulogram (a type of X-ray study done with dye injected directly into the fistula) is performed. The fistulogram doubles as both a diagnostic tool and a treatment opportunity, since your interventional radiologist can often fix the problem during the same procedure.
How a Failing Fistula Is Treated
The treatment depends on what’s causing the failure. The most common approach is a percutaneous intervention, meaning it’s done through a small needle puncture rather than open surgery. During this procedure, an interventional radiologist or nephrologist threads a thin catheter into the fistula and uses one or more techniques to restore flow.
If narrowing is the culprit, balloon angioplasty is the standard fix. A tiny balloon is inflated inside the narrowed section to widen it. If a clot is present, it can be removed mechanically (pulled or suctioned out), dissolved with clot-busting medication, or cleared with a combination of both approaches. These procedures are typically done under local anesthesia, and you’re awake for them.
The good news is that the immediate success rate for these interventions is high. One study of patients with failing hemodialysis access found a 100% technical success rate for endovascular procedures. The longer-term picture is more modest: about 72% of treated fistulas were still working at six months, and 32% at one year. That means repeat procedures are common, and your team will monitor you closely afterward.
If the fistula can’t be salvaged with a catheter-based procedure, surgical thrombectomy (removal of the clot through an incision) is an option. In cases where the fistula is beyond repair, your vascular surgeon will discuss creating a new fistula, usually in a different location on the same arm or on the other arm.
What Happens to Your Dialysis in the Meantime
If your fistula can’t be used and you need dialysis before it’s repaired, your team will place a temporary catheter, usually in a large vein in the neck or chest. This provides immediate access for dialysis but comes with a higher risk of infection compared to a fistula. Temporary catheters are meant to be a bridge, not a long-term solution, and your team will prioritize restoring your fistula or creating a new one as quickly as possible.
Catheters come in two types: cuffed (designed for weeks of use) and non-cuffed (designed for days). Which one you get depends on how long your team expects the repair to take. Either way, the goal is to get you back on a functioning fistula as soon as it’s safe to do so.
Protecting Your Fistula Going Forward
Once your fistula is working again, daily monitoring becomes even more important. Check for the thrill at least once a day, ideally at the same time so you develop a sense of what your normal baseline feels like. A subtle change in the strength of that vibration can be an early sign of new narrowing, well before a clot forms.
Protect the arm with your fistula from anything that compresses the blood vessels. That means no blood pressure cuffs on that arm, no tight sleeves or jewelry, and no sleeping on it. Stay well hydrated, since dehydration thickens the blood and increases clotting risk. If you tend to have low blood pressure during or after dialysis, talk to your team about adjustments, because drops in blood pressure are a known trigger for fistula clotting.
Keep all your dialysis and nephrology appointments, even when things feel fine. Many clinics routinely monitor fistula flow rates during dialysis sessions, and a gradual decline in flow is one of the earliest detectable warning signs of developing stenosis. Catching narrowing before it causes a clot is far easier to treat and gives your fistula the longest possible life.