Renal Failure & Dialysis Access
Dialysis is a technique of artificially cleaning blood in patients with severe kidney (renal) disease. The treatment removes impurities and waste products from the blood, regulates body water levels and maintains electrolyte balance. Dialysis can be performed by using either of two methods, peritoneal dialysis or haemodialysis. Peritoneal dialysis uses the peritoneal membrane, the lining of your abdomen whereas haemodialysis requires a dialysis machine and relies on direct communication with large blood vessels to clean the blood.
Dialysis access can be temporary or permanent:
Temporary access: - A tube (catheter) is placed into the large vein in the upper chest to allow access. Dialysis catheters are recommended for temporary access and are used for emergencies or for short periods. Tunnelled catheters can be used for longer periods.
Permanent access: Permanent access is created by surgically joining together veins and arteries to form either an Arterio-venous fistula (AVF) or Arterio-venous graft (AVG).
- AV Fistula: An AV fistula is created by joining a large vein to a nearby artery. The large vein is divided and stitched to the opening made at the side of artery. This is commonly at the wrist or near the elbow crease. High pressure arterial blood flows into the vein which over time enlarges or "matures" at which point it allows for reliable access for dialysis.
- AV Graft: The connection between an artery and vein can be made using a synthetic bridge (graft). Grafts are used if your veins are unsuitable or blocked. One end of the graft is stitched to one a vein and the other end is connected to an artery. The graft is placed either straight but more commonly as a loop under the skin of lower arm. A synthetic AV Graft can also be constructed in a leg.
An assessment of your veins and arteries prior to creating dialysis access is very important. Before dialysis access is created, your vascular surgeon will commonly order an ultrasound assessment of blood vessels in your arms and/or legs. It is important to know that the atrial supply of blood flowing towards the access site is normal and, that the veins that will make up the access site are present and of a good quality. Using a diseased artery or a small or blocked vein will result in inadequate blood flow and failure of the access site.
It is important that over the time the AV Fistula or Graft increases in size (matures) making it easier for the dialysis staff to use it. It also means that enough blood passes through it so that the blood is cleaned efficiently. Compared to AV fistula, AV grafts mature quickly however they have the disadvantage of being more prone to infection.