Having an arteriovenous fistula (AVF) for dialysis. What I tell my patients:
Why do I need a fistula for dialysis?
As your native kidney function deteriorates, a means of replacing the job of the kidneys, known as ‘renal replacement therapy’, is needed. The best way overall is to have a kidney transplant, but if there is not a transplant option, or if you are on the waiting list for a transplant, dialysis is necessary. This can be peritoneal dialysis or most commonly haemodialysis.
In haemodialysis, blood is removed from the bloodstream and passes through a dialysis machine. This acts like an artificial kidney, removing impurities that have built up, and returning ‘clean’ blood back into the body. In order to do this, there needs to be a route of entry or ‘vascular access’ into the bloodstream of which there are three kinds; a arteriovenous fistula, a graft or a central venous catheter. A fistula is the preferred means of access and the thrust of this article. However patient preference is very important and has a large influence on the choice of vascular access.
What is a fistula and how is it formed?
Blood is pumped through the dialysis machine at reasonably high speeds so normal ‘blood test veins’ are simply not strong enough and would collapse under the pressure. The ideal is a ‘stronger’ blood vessel, easily accessible and sitting just under the skin. This ideal is a fistula. It is created by surgically connecting a vein to an artery typically in the wrist or elbow area. This allows a proportion of fast flowing blood from the artery to be diverted up the vein. The vein adapts to this faster volume of blood by slowly thickening up, enlarging and becoming strong enough to withstand regular needling necessary for dialysis. Where possible it is made in the non-dominant arm which means that if you are right-handed, the surgeon will use your left arm and vice versa.
Can all patients with renal failure have a fistula?
Not all renal patients can have a fistula. There must be appropriate sized blood vessels in the arm. Vessels are assessed by clinical examination in clinic this might be sufficient to place you on the operating list for fistula creation. However if the vessels are not easily visible, ‘duplex mapping’ (an ultrasound scan to accurately measure arteries and veins) can be done.
Sometimes the arm veins are not large enough. Or they have been damaged by numerous blood tests or insertion of cannulae as part of previous medical treatment. This is why kidney patients are advised to protect their veins at forearm and elbow level in the non-dominant arm.
Other vascular access options
The best vascular access choice is a fistula, however, if the veins are unsuitable, there are two other options. The first is a ‘graft’. It is a prosthetic or plastic tube connecting an artery to a vein with blood flowing through it so it that can be needled like a fistula. The main problem with a graft is that because it is ‘foreign’ material it can be prone to infection.
A central venous catheter is another option. Plastic catheters are placed in the great veins leading to the heart. The exit site for these catheters is usually the chest wall. Again this involves plastic material prone to infection, the infection risk being greater than a graft, but in certain circumstances, such as short-term dialysis or for frail or elderly patients, it is often a sensible option despite long-term complications.
What does the fistula operation involve and what should I look out for after the surgery?
To create the fistula it is necessary to have a small operation done, as ‘day-case procedure. This means there is no need to stay overnight. It is typically done under local anaesthetic - you are awake during the procedure, can chat with the surgeon throughout and even listen to music. In fact in my theatre, the patient always has first choice of the type of music! The operation lasts about an hour. Once the fistula is created, there will be a ‘buzz’ in the vein. The surgeon will show you how to feel this buzzing and it is your way of checking that the fistula is working.
Not all fistulas made will work and this is important to know before having the procedure. However after the operation there are things you can do to help develop the fistula and stop it clotting off. Drinking plenty to keep well hydrated is essential – this prevents the blood becoming ‘sticky’ and so more likely to clot. Exercising the fingers and hands on the same arm as the fistula, for example by squeezing a pair of socks or rubber ball for 5 minutes, 5 times a day encourages blood flow.
If the ‘buzz’ disappears, then please alert your dialysis nurse or doctor. There are rescue procedures that can be done to restore flow in the fistula.If the site of the fistula operation becomes red or swollen, this may be the sign of a wound infection and you should see your doctor. Occasionally too much blood flow is diverted to the fistula and the hand might become cooler. If you notice this, please tell your doctor. Pins and needles in the hand after surgery can be due to bruising around the nerves and usually settles in a few days.
For a few days after the operation it is a good idea to elevate the arm whilst relaxing at home and not use your arm for lifting heavy bags or weights. Once the wound is fully healed and the fistula is working well, there are no restrictions and you can use your arm as normal. Driving is usually fine after a couple of weeks.Once the fistula has been created, it is vital not to have blood tests or measure blood pressure in the fistula arm. Both of these could potentially damage or clot the fistula.
Potential Complications after Fistula Surgery
- Failure to mature
- Wound infection
- Steal syndrome
- Becoming unsightly with time
When can my fistula be used for dialysis?
The fistula usually takes about 6 weeks to mature and it this point it is ready to be ‘needled’ for dialysis. However, some mature in much less time and some take longer. Your surgeon or dialysis nurse can examine the fistula and give you an indication of its maturity.
When first used, the walls of the fistula might be soft and mobile and so inserting the needle for the first few dialysis sessions may be difficult and bleeding can occasionally occur at the puncture site. This is not uncommon and whilst the bruising may be unsightly, it usually settles within a few days. The dialysis nurse is then able to make further attempts at inserting the needle. With time, the vessel becomes fixed in position and the vessel wall stronger, meaning few or no further problems when the needle is inserted.
Are there long-term problems with the fistula?
As the fistula matures and is needled, the vein still remains reasonably small and discreet. Sometimes though, the vein enlarges and becomes unsightly. This is usually due to either needling the same portion of vein too many times or due to a narrowing within the fistula somewhere ‘upstream’. The fistula can be surgically repaired to make it cosmetically acceptable again. A narrowing can be opened out using minimally invasive techniques by a radiologist and this is known as a fistuloplasty.
If the fistula becomes overly developed, it can ‘steal’ blood intended for the hand. Sometimes the hand is a little cooler and may not a problem. However this ‘steal syndrome’ can cause pins and needles or pain in the hand and at this point needs to be sorted out. Surgery can reduce the flow in the fistula therefore more blood flows into the hand to relieve the symptoms.
- There are three types of vascular access for haemodialysis
- Each patient has a say in the best form of vascular access for them
- A fistula does not involve plastic or ‘foreign’ material therefore decreasing infection risk
When nearing dialysis, it is important to protect the veins in your arm from blood tests, particularly at the elbow crease.