Vascular access is the circulatory site that allows the connection between the patient's circulation and the dialyzer.
The two most common types of chronic access used for hemodialysis are: 1) Arterio-venous (AV) fistula and 2) Arterio-venous (AV) graft
This is created internally and is used for prolonged periods of time. This involves a small operation to join an artery and vein, allowing arterial blood to flow directly into the vein.
The blood vessels of the arm are usually chosen, e.g. at the wrist or at the upper forearm. Due to the arterial pressure, the vein will increase in size and its walls will thicken. It takes about 3 to 7 weeks for the fistula vein to mature. It is then easier to put a needle into this vein to allow blood to flow through the dialyzer using the blood pump on the machine.
The arterio-venous graft (AVG) is an artificial blood vessel used to join artery and vein. It is used when the patient's own blood vessels are too small for fistula construction. Often, these patients are the elderly or have pre-existing diabetes mellitus. The graft, which may be either straight or looped, is close to the surface of the skin for easier needle insertion. The graft may be of an artificial material such as polytetrafluoroethylene or Gortex, or can be obtained from the patient's own body, e.g. the vein in the thigh.
Grafts are most commonly placed in the upper arm, lower arm, and thigh. Two to four weeks should pass before the graft is punctured to allow adequate healing and sufficient growth of tissue to stabilize the graft.
These are temporary or immediate accesses created for use in cases where urgent dialysis is needed, and the patient cannot wait weeks for the AV fistula to be ready for use. These include 1) the subclavian catheter, 2) internal jugular catheter and 3) arterio-venous shunt.
The subclavian catheter is a tube which is inserted into the subclavian vein near the neck. The internal jugular catheter is placed in the veins by the side of the neck. It cannot be used beyond a few weeks as it tends to get blocked by clotting blood or the site of insertion gets infected.
An arterio-venous shunt is surgically created which consists of two pieces of silastic tubing, each with a Teflon tip on one end. The Teflon tip of one piece of the shunt tubing is placed in an artery and the Teflon tip of the other is placed in an adjacent vein. The tubing is then brought through two puncture wounds in the skin and connected. The AV shunt has limited life-span due to clotting or infection and does not usually work for longer than 6 months whereas an AV fistula can be used for years.
For more information on Vascular Access see the National Kidney Foundation guidelines