Hemodialysis works by circulating the blood through special filters. Before hemodialysis can be performed, there needs to be adequate access to the circulatory system. However, a normal IV will not support the volume required for hemodialysis. For this reason, a special type of arterial and venous access is established.
The access can be either external or internal. External access involves two catheters — one that is placed in an artery and one in a nearby vein, or two catheters positioned within different parts of a large vein. External access is typically only used in emergency situations.
Internal access can be either an arteriovenous (AV) fistula or graft. A fistula involves the surgical joining of an artery and vein under the skin. The increased blood volume stretches the elastic vein to allow a larger volume of blood flow. After the four to six weeks the fistula needs to heal, needles can be placed so that arterial blood can be pulled off for dialysis and the cleansed blood returned through the dilated vein.
A graft may be used for people whose veins are not suitable for a fistula. This procedure involves surgically grafting a donor vein from the patient's own saphenous vein (in the leg), a carotid artery from a cow or a synthetic graft from an artery to a vein. After there is adequate access with two ports, a hemodialysis machine is connected to cleanse the blood.