Dialysis

Alternative names:

artificial kidneys; AV fistula; AV graft; hemodialysis; peritoneal dialysis

How the test is performed:

PERITONEAL DIALYSIS
Peritoneal dialysis works by using the peritoneal membrane inside the abdomen as the semipermeable membrane. Special solutions that absorb toxins are infused in, remain in the abdomen for a time, and then drained out.

HEMODIALYSIS
Hemodialysis works by circulating the blood through a machine. The blood flows across a semipermeable membrane with solutions that remove 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, then both are joined externally. 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 will remove specific soluble materials from your blood.

In children, hemodialysis is used as preparation for kidney transplant rather than for chronic care.

How to prepare for the test:

Blood pressure medications are frequently withheld 6 to 12 hours before hemodialysis, as are water soluble vitamins. Also, it is best to eat before treatment, since dialysis can take 4 to 5 hours and you will not be permitted to eat during the procedure.

Just before your health care provider begins the hemodialysis procedure, the following assessments will be made:

• blood pressure
• temperature
• heart rate
• respiratory rate
• weight
• chest assessment
• examination of venous access
• if you need the procedure explained

How the test will feel:

Since dialysis takes several hours, it may become tedious. With children it is especially important to have games, something to read, or other distractions.

Why the test is performed:

This procedure is performed to remove contaminants from the blood that could and eventually would result in death in the absence of kidney function.

The kidneys function as filters for the blood, removing products of amino acid breakdown. More than that, they serve to reclaim and regulate body water, maintain electrolyte balance, and ensure that the blood pH remains between 7.35 and 7.45. Without the function of the kidney, life is not possible.

Dialysis serves to replace some of the functions of the kidney. Since dialysis is not an constant ongoing process, it cannot serve as a constant monitor as do normal functioning kidneys, but it can eliminate waste products and restore electrolyte and pH levels on an as needed basis.