Clotted AV fistula: signs, what to do and how fast
A thrombosed arteriovenous fistula leaves the patient without their dialysis access. If it is not reopened quickly, it usually ends in a central venous catheter and sometimes in permanent loss of the fistula. This guide explains how to recognize it, what to do in the unit, why time matters, how it is treated and how to prevent it.
Key points
- It is an emergency. Declotting should be attempted within the first 48 hours, to avoid a central venous catheter [2].
- Suspect it when there is no thrill and no bruit. Sometimes there is a hard, tender cord, or cannulation gives no flashback and clots are aspirated.
- There is almost always a stenosis behind it: it accounts for 80–85% of thromboses. The rest are due to hypotension, compression, hematomas or other non-anatomical causes [2].
- It is treated with endovascular or surgical thrombectomy, correcting the stenosis that caused it at the same time. For native fistulas, no randomized trials compare the two approaches [1].
- In Spain, the "Fistula Code" (GEMAV with the patient associations ALCER and ADER) organizes urgent referral to the vascular access unit [2].
How to recognize it
| Where | What you find |
|---|---|
| Exam | No thrill and no bruit anywhere along the course. Sometimes a hard, cord-like, tender and red vein. The patient may say the fistula "stopped buzzing". |
| At cannulation | No flashback, or clots are aspirated. Do not needle repeatedly to "check". |
| Ultrasound | The vein is filled with material, does not compress and has no color Doppler flow. Fresh thrombus is hypoechoic or anechoic; older thrombus is more echogenic [5]. The feeding artery reverts to a high-resistance waveform. |
Thrombosis can be partial: the thrill fades, the blood pump speed cannot be reached or clots are aspirated, but some flow remains. That is urgent too, because it usually progresses.
What to do in the unit
- Do not cannulate the fistula. Needling a clotted fistula does not clear it and adds hematomas that make rescue harder.
- Confirm with an exam of the whole course and, if available, with ultrasound.
- Ask when it last worked: the last thrill the patient felt and the last normal session. Time since onset shapes the treatment.
- Alert nephrology and the vascular access team immediately, following any local urgent-referral pathway [1].
- Plan dialysis with the team: if dialysis is needed before the rescue, the catheter decision is theirs.
- Do not massage the fistula or try to clear it by aspiration.
- Document the findings, the time and who was told, plus recent session problems: pressures, flows, prolonged bleeding, difficult cannulation or hypotension.
Why time matters
Over hours, the thrombus organizes and sticks to the wall, and rescue gets harder. Every day without the fistula is also another day on a catheter, with its risk of infection and central venous stenosis. That is why declotting should be attempted within the first 48 hours [2]. Local protocols vary, and some hospitals repair the fistula within 24 hours so that no catheter is needed. The Spanish GEMAV guideline sets a quality standard of rescuing more than 70% of potentially salvageable thrombosed fistulas [1].
How it is treated
- Endovascular: clot removal by mechanical thrombectomy, thrombolysis or a combination, with angioplasty of the causative stenosis in the same procedure [2].
- Surgical: thrombectomy with an embolectomy catheter and, often, a new anastomosis a few centimeters more proximal or a bypass graft [2]. For a native fistula clotted because of a juxta-anastomotic stenosis, GEMAV recommends surgery as the first choice, provided it does not require a central venous catheter [1].
For native fistulas there are no randomized trials comparing surgery with endovascular treatment, so guidelines accept both, depending on the lesion and the center's experience [1,3]. What is not up for debate is fixing the cause: without treating the stenosis, thrombosis tends to recur.
Why fistulas clot
- Significant stenosis: 80–85% of cases [2]. See AV fistula stenosis.
- Non-anatomical causes (15–20%) [2]:
- hypotension during or after dialysis, and dehydration;
- external compression: tight dressings, hemostasis that stops the thrill, sleeping on the arm or taking blood pressure on it;
- hematomas and infiltrations: in one series, 26% of major infiltrations ended in thrombosis [4];
- hypercoagulable states and low cardiac output.
How to prevent it
- Find and treat stenosis before it clots: an exam at every session (see the AV fistula physical exam) and prompt workup of any change.
- Hemostasis without occlusion: compress the puncture site while keeping a palpable thrill above it. Never use clamps on a graft.
- Avoid hypotension during and after dialysis, adjusting ultrafiltration with the team.
- Prevent infiltrations (see fistula infiltration).
- Teach the patient to check every day that the fistula buzzes, to avoid compressing it (clothing, watches, sleeping on it, blood pressure cuffs) and to call straight away if they cannot feel it.
Frequently asked questions
How do I know if a fistula is clotted?
There is no vibration (thrill) to feel and no bruit to hear anywhere, and sometimes the vein is hard and tender. Ultrasound confirms it: the vein does not compress and has no Doppler flow.
How long do you have to declot a fistula?
Declotting should be attempted within the first 48 hours. The sooner, the better the chance of success and the lower the need for a central venous catheter.
Can you cannulate a clotted fistula?
No. Needling it does not clear it and adds hematomas that make rescue harder. Alert the vascular access team and plan dialysis another way if needed.
Why does a fistula clot?
In 80–85% of cases, because of a stenosis. The rest are due to hypotension, dehydration, compression of the arm, hematomas or clotting disorders.
How is a clotted fistula treated?
With endovascular thrombectomy (mechanical, with drugs or combined) or surgical thrombectomy, correcting the stenosis that caused it at the same time. The choice depends on the lesion and the center's experience.
What should patients do if their fistula stops buzzing?
Contact their dialysis unit or the emergency service straight away, without waiting for the next session. Every hour counts to save the fistula.
Educational content. It does not replace supervised hands-on training or your unit's protocols.
References
- Ibeas J, Roca-Tey R, Vallespín J, Moreno T, et al. Spanish Clinical Guidelines on Vascular Access for Haemodialysis (GEMAV). Nefrología. 2017;37(Suppl 1):1-191. doi.org
- Roca-Tey R, Gruss E, Ibeas J. Trombosis de la fístula arteriovenosa [Arteriovenous fistula thrombosis; in Spanish]. Nefrología al día. nefrologiaaldia.org
- Lok CE, Huber TS, Lee T, Shenoy S, et al. KDOQI Clinical Practice Guideline for Vascular Access: 2019 Update. Am J Kidney Dis. 2020;75(4 Suppl 2):S1-S164. doi.org
- Lee T, Barker J, Allon M. Needle infiltration of arteriovenous fistulae in hemodialysis: risk factors and consequences. Am J Kidney Dis. 2006;47(6):1020-1026. doi.org
- Sharbidre KG, Alexander LF, Varma RK, et al. Hemodialysis access: US for preprocedural mapping and evaluation of maturity and access dysfunction. RadioGraphics. 2024;44(1):e230053. doi.org