Dialysis access: AV fistulas, grafts and catheters explained

Why dialysis access matters

Haemodialysis works by drawing blood from the body, passing it through a machine that filters out waste products and excess fluid, and returning it. To do this three times a week, every week, you need a reliable, robust access point in the bloodstream that can withstand repeated use.

Ordinary veins are too fragile for this. The walls are thin and would collapse or scar quickly under repeated needling and the high flows required. The solution is to create a dedicated access point that is purposely strengthened for dialysis use.

The quality of your dialysis access has a direct effect on the quality of your dialysis and your health. Poor access means interrupted treatment, hospital admissions and reduced life expectancy. This is why planning access well in advance of starting dialysis is so important.

The three types of dialysis access

When should access planning begin?

The timing of access creation is critical. ESVS guidelines recommend referral for access planning when the eGFR (estimated glomerular filtration rate, a measure of kidney function) falls below 15 to 20 mL/min per 1.73 m2. This is typically at least 6 months before dialysis is expected to start.

Creating a fistula early gives time for it to mature fully before it is needed. Starting too late means relying on a tunnelled catheter as a bridge, which increases infection risk and can cause scarring in the central veins that makes future access more difficult.

Your kidney team (nephrologist) will refer you to a vascular surgeon for access planning as your kidney function declines. If you have not yet been referred and your eGFR is below 20, ask your team about access planning.

What happens at the access planning appointment

At a vascular surgery access planning appointment, the surgeon will take a history including your kidney disease, diabetes status, previous access attempts, and any arm surgery or injury. A detailed examination of both arms is performed, feeling the arteries and veins.

A pre-operative vein mapping Doppler ultrasound is then performed. This is a painless scan that images the veins and arteries in both arms to identify the best vessels for fistula creation. Studies consistently show that pre-operative mapping improves fistula maturation rates and long-term outcomes compared to clinical assessment alone.

The scan looks for:

• Vein diameter (minimum 2.5 mm is generally required for a wrist fistula)
• Vein depth (deep veins are harder to needle for dialysis)
• Arterial flow and diameter at the proposed anastomosis site
• Any previous scarring, stenosis or occlusion in the central veins (from previous catheters)

The AV fistula operation

AV fistula creation is typically done as a day case under local anaesthetic, though general or regional anaesthesia is used if preferred by the patient or if the anatomy is complex. The operation takes approximately 45 to 90 minutes.

The surgeon makes a small incision at the chosen site, identifies the artery and vein, and creates a side-to-end or end-to-side connection between them using very fine sutures under surgical magnification. Blood immediately flows from the artery into the vein, which you can feel as a thrill (a buzzing sensation) at the anastomosis site.

The most common sites in order of preference are:

• Wrist (radiocephalic): radial artery to cephalic vein at the wrist. Preferred first option where anatomy allows. Longer maturation time but best long-term patency
• Upper arm antecubital (brachiocephalic): brachial artery to cephalic vein at the elbow crease. Used when wrist vessels are unsuitable. Matures faster and has higher blood flow, but carries a higher risk of steal syndrome (see below)
• Brachiobasilic transposition: brachial artery to basilic vein in the upper arm. The basilic vein runs deep and must be surgically repositioned (transposed) to a more superficial position for needling. A more complex operation but useful when other sites have been exhausted

Fistula maturation: what to expect

After surgery, the fistula needs time to mature before it can be used for dialysis. Maturation means the vein has enlarged enough and its wall has thickened enough to withstand repeated needling. This typically takes 6 to 8 weeks for a wrist fistula and 6 to 12 weeks for an upper arm fistula.

You will be asked to do fistula exercises: repeatedly squeezing a soft ball or rubber ring with the fistula arm for several minutes a few times each day. This promotes blood flow through the fistula and encourages the vein to mature more quickly.

Maturation is confirmed at a follow-up appointment with clinical examination and Doppler ultrasound. The fistula is assessed for adequate diameter (at least 6 mm for reliable needling), adequate depth (no more than 6 mm from the skin surface) and adequate blood flow (at least 500 to 600 mL per minute).

When a fistula does not mature

Unfortunately, approximately 40 to 50% of newly created AV fistulas fail to mature adequately. This is the most significant challenge in dialysis access surgery and is the reason the UK currently has difficulty meeting the recommended target of 80% of prevalent dialysis patients on permanent access (rather than a catheter).

Failure to mature is most commonly caused by a stenosis (narrowing) at or near the fistula, or by competitive flow through a side branch that diverts blood away from the main vein. Both of these are potentially correctable.

When a fistula fails to mature, the options include:

• Balloon angioplasty: a catheter procedure to dilate a stenosis in the fistula vein
• Surgical ligation of competing branches: tying off side branches that are stealing flow from the main fistula vein
• Fistula revision: surgical revision of the anastomosis if the connection itself is the problem
• New fistula at an alternative site

Managing a functioning fistula long-term

A well-functioning fistula requires ongoing care and monitoring. Most dialysis units have a dedicated access surveillance programme using regular clinical assessment and Doppler ultrasound.

The most common long-term problem is stenosis: a narrowing that develops, usually near the anastomosis or in the outflow vein. Stenosis reduces blood flow and dialysis adequacy and, if untreated, can lead to fistula thrombosis (clotting off). Regular monitoring allows stenoses to be identified and treated before the fistula clots.

Treatment of fistula stenosis is usually with balloon angioplasty, which can be done as a day case procedure. Stenting is used selectively for recurrent or resistant stenoses. Surgical revision is considered when endovascular options have been exhausted.

Fistula thrombosis

If a fistula clots, the thrill (buzzing sensation) disappears and the fistula becomes soft and non-pulsatile. This is an urgent problem. Contact your dialysis unit or the on-call vascular surgery team immediately. Declotting is most successful when performed within hours of thrombosis, either surgically or with catheter-directed thrombolysis.

Steal syndrome

Steal syndrome occurs when the fistula diverts so much blood from the artery that the hand downstream from the fistula does not receive enough flow. Symptoms include hand pain during dialysis or exercise, coldness, numbness or weakness in the hand, and in severe cases ischaemic ulceration. Steal is more common with high-flow upper arm fistulas. It requires urgent vascular assessment and may need surgical revision to reduce fistula flow.

Fistula aneurysms

Over years of use, the repeated needling of a fistula can cause the vein to develop aneurysmal dilations (bulges). Small aneurysms are very common and usually harmless. Large aneurysms, or those with overlying thin skin at risk of rupture, may need elective surgical repair to preserve the fistula and prevent bleeding.

Tunnelled dialysis catheters (TDC)

A tunnelled dialysis catheter is placed when immediate dialysis access is needed and a fistula is not yet ready. It consists of a dual-lumen tube (one channel takes blood to the machine, the other returns it) inserted into a central vein, most commonly the internal jugular vein in the neck, and tunnelled subcutaneously to exit at the chest wall.

TDCs can be used immediately after placement and are managed by the dialysis nursing team. The exit site requires regular cleaning and dressing changes. Patients should keep the exit site dry and report any redness, pain or discharge promptly.

The two main risks of TDCs are infection (including serious blood stream infections) and thrombosis. They should be considered a bridge to permanent access, not a permanent solution. Every effort should be made to create and mature an AV fistula so the catheter can be removed as soon as possible.

What to do next

If you have chronic kidney disease and have not yet had access planning, ask your kidney team about referral to vascular surgery. Early planning is the single most effective way to ensure you start dialysis with a working fistula rather than a catheter.

If you have an existing fistula with concerns about maturation, function or complications, a specialist vascular access assessment can provide a prompt review and plan.