Introduction
An arterio-venous fistula (AVF) is created to allow patients to undergo haemodialysis. Haemodialysis is used to treat patients who have kidney failure and is an artificial way for cleaning the patients’ blood and removing toxic products. It is a very important lifesaving procedure.
To allow haemodialysis a large volume of blood needs to be pumped through a dialysis machine. Normal veins that are used for IV cannula do not have enough blood flow to allow this. Larger veins within the abdomen and chest do have enough blood flow and at times a catheter (tube) is placed into these veins to facilitate dialysis. These lines have to protrude outside of the body and therefore have risks of infection and blockage.
A better alternative is the creation of an arterio-venous fistula. This is the process of joining a vein from the arm or leg, onto an artery so that some of the arterial blood flow is directed through the vein. This allows a suitably large volume of blood to flow through the vein that can then be used for dialysis. As these veins are quite close to the skin they can readily be accessed.
AVF are preferable in the arm, however their position is dictated by having suitable veins. At times artificial grafts can be used for fistula creation, however these are quite prone to infection and occlusion.
Indications
AVF creation is primarily used for dialysis. In some situations where regular repeated access to veins is required for other medical treatments an AVF may be created.
The timing of AVF creation is determined by the treating kidney specialist (nephrologist). It does take 6 weeks after creation of the fistula to be ready for use. Because of this lag time, having a fistula ready for use is desirable in patients whose kidney function is deteriorating.
Preoperative Instructions
Fistula creation may be performed under general or local anaesthesia depending on the site selected. Ultrasound scans to identify suitable veins and arteries will be arranged prior to booking surgery. The actual site of the fistula will mainly depend on the size of the veins. Usually, the fistula is created either at the wrist or elbow crease. Review of usual medications will need to be undertaken, particularly with regards to blood thinners and diabetic medications. Fasting times will be advised when the procedure is booked.
Procedure
The actual procedure of AV fistula creation involves exposing the vein that is to be used for the fistula and then suturing (anastomosing) that vein onto the side of the appropriate artery. This allows some of the arterial blood flow to pass through the vein, back up the arm and to the heart. The wound is quite superficial and closed with some dissolving sutures that will not require removal. Most patients will be monitored overnight following the procedure and discharged the following morning.
Postoperative Instructions
Post operatively, the dressing should be left on for 3 days. After that time the dressing can be removed, and the wound washed in the shower. The wound can be left open thereafter. Once at home it is important to use the arm as much as possible. It is normal to have a degree of swelling after the surgery and elevation of the arm on 1-2 pillows will generally help.
A follow up appointment will be scheduled for approximately 2 weeks and then an ultrasound scan performed at 6 weeks after the surgery. It does take 6 weeks for the vein to become suitable to start using for dialysis. In the 6-week period, the vein wall will thicken in response to the increased blood flow and pressure. The thickening of the vein wall allows it to be punctured safely to facilitate dialysis.
When a fistula is first being used it is quite common to develop bruising at the needle puncture sites. As the fistula continues to improve the amount of bruising should reduce. Regular follow up reviews and ultrasound scans will be arranged to monitor the fistula.
Risks
Arterio-venous fistula are important to allow life saving dialysis. Whilst the fistula surgery is very safe a number of potential complications can occur. These complications can develop immediately after surgery or over time. It is quite common for fistula to need some maintenance interventions over the years. This may include balloon angioplasty, stenting or surgical revision. At times, some fistulas require removal and the development of a new fistula at a different location.
The potential complications that can occur include:
- Anaesthetic complications – reaction to medications or stress on pre-existing heart or lung Issues.
- Bleeding.
- Wound infection.
- Occlusion of the fistula – damaged or scarred veins have poor flow and can cause a fistula to occlude. Whilst not dangerous it does mean the fistula will not work and an alternative option will need to be considered. Depending on the quality of the vein, re-operation would be considered to try and ensure the fistula works.
- Arm swelling – it is normal to have a degree of arm swelling, however in some situations this can be excessive. Swelling develops, as the fistula does mean that more blood flow is entering the veins. If there is scarring in the veins higher up the arm or in the chest then a back pressure can build up and cause swelling. This can be a problem in patients with pacemakers or pre-existing lines for dialysis which can scar and narrow the main veins in the chest.
- Steal – this is the process where too much blood is diverted into the fistula and then not enough reaches the hand. It can cause a critical lack of blood flow to the hand which can cause ulcers or wounds. It can be very painful and will need correction. Further revision of the fistula may correct the symptoms, however, at times the fistula will need to be removed.
- Stenosis – over time, scar tissue can build up within the fistula and cause narrowing (stenosis) to develop. This can reduce the blood flow through the fistula and potentially make dialysis difficult, impossible or ineffective. The narrowing may be corrected by balloon angioplasty, stenting or surgical correction. In severe cases a new fistula will be required. The scar tissue develops due to the higher blood flow than normal for a vein. It is the nature of fistula and is difficult to avoid or prevent.
- Nerve injury – nerves close to the veins can be stretched or traumatised from the surgery. This can cause some altered sensation or numbness in the forearm or hand.
- Heart failure – rarely, too much blood flow through the fistula can stress the heart. This occurs mainly in people with significant underlying heart disease, and fistula creation may therefore not be possible
- Aneurysm – most fistula will dilate to a certain degree. This is useful as it allows easier access for dialysis. Occasionally the vein can dilate too much and become an aneurysm. Whilst this can develop into quite a large visible vein, they rarely cause problems. In some situations, if they are very large then surgical removal would be considered.
Treatment Alternatives
Dialysis access is critical to provide a means for haemodialysis. Th only 2 options are a fistula or a tunneled venous catheter (line). The AVF does provide a much better long-term option, however lines are used when dialysis is required urgently or if no suitable veins are available to create and AVF. There are many options for the site of an AVF and the most suitable site is individualised for each patient.
Related Information
Arterial Bypass Surgery
Peripheral Artery Balloon Angioplasty
Peripheral Artery Stenting
Dialysis Acess