Dialysis

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How is the Test Performed?

PERITONEAL DIALYSIS
Peritoneal dialysis works by using the peritoneal membrane inside the abdomen as the semipermeable membrane. Special solutions that facilitate removal of toxins are infused in, remain in the abdomen for a time, and then drained out. This form of dialysis can be performed at home, but must be done on a continuous everyday basis.

HEMODIALYSIS
Hemodialysis works by circulating the blood through special filters. The blood flows across a semipermeable membrane (the dialyzer or filter), along with solutions that help facilitate removal of toxins. Before hemodialysis can be performed, there needs to be adequate access to the vascular system. The access needs to support a blood flow of 250 milliliters per minute (ml/min), and a normal venous peripheral IV will not support that volume of blood flow. A special type of arterial and venous access is therefore established.

The access can be either external or internal. External access involves two catheters -- one that is placed in an artery, and one in an adjacent 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 AV graft. An AV 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 4 to 6 weeks the fistula needs to heal, needles can be placed so that arterial blood can be pulled off for dialysis, and the cleansed blood returns through the dilated vein. Turbulent blood flow over the AV fistula is commonly felt and termed a thrill.

An AV graft may be used for people whose veins are not suitable for an AV 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. The port from the artery leads into the machine, and the port returning from the machine leads into the vein. Inside the machine, your blood is run through tubes with semipermeable membranes, and the tubes are bathed with solutions that help remove specific soluble materials from your blood.

In children, hemodialysis is used as preparation for kidney transplant, rather than for chronic care. In adults with chronic kidney failure, hemodialysis is typically performed over 3 to 4 hours three times a week.