Medical Encyclopedia


Medical Encyclopedia

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Contents of this page:


Kidney anatomy
Kidney anatomy
Kidney - blood and urine flow
Kidney - blood and urine flow

Alternative Names    Return to top

Artificial kidneys; Hemodialysis; Peritoneal dialysis; Renal replacement therapy

Definition    Return to top

Dialysis is a method of removing toxic substances (impurities or wastes) from the blood when the kidneys are unable to do so.

How the Test is Performed    Return to top

Dialysis can be performed using several different methods.


Peritoneal dialysis filters waste using the peritoneal membrane inside the abdomen. The abdomen is filled with special solutions that help remove toxins. The solutions remain in the abdomen for a time and then are drained out. This form of dialysis can be performed at home, but must be done every day.


Hemodialysis works by circulating the blood through special filters outside the body. The blood flows across a filter, along with solutions that help remove toxins.

Dialysis uses special ways of accessing the blood in the blood vessels. The access can be temporary or permanent.

Temporary access takes the form of dialysis catheters -- hollow tubes placed in large veins that can support acceptable blood flows. Most catheters are used in emergency situations for short periods of time. However, catheters called tunneled catheters can be used for prolonged periods of time, often weeks to months.

Permanent access is created by surgically joining an artery to a vein. This allows the vein to receive blood at high pressure, leading to a thickening of the vein's wall. This vein can handle repeated puncture and also provides excellent blood flow rates.

The connection between an artery and a vein can be made using blood vessels (an arteriovenous fistula, or AVF) or a synthetic bridge (arteriovenous graft, or AVG). Your health care provider may suggest an AVF, because it has lower infection rates and better long-term function than an AVG.

Blood is diverted from the access point in the body to a dialysis machine. Here, the blood flows counter-current to a special solution called the dialysate. The chemical imbalances and impurities of the blood are corrected and the blood is then returned to the body. Typically, most patients undergo hemodialysis for three sessions every week. Each session lasts 3 - 4 hours.

How to Prepare for the Test    Return to top

When possible, patients should prepare for dialysis before dialysis is absolutely necessary.

It is important to stick to the diet and medicines prescribed by the dialysis staff and your kidney specialist (nephrologist).

The health care provider will make the following assessments before beginning the hemodialysis procedure:

How the Test Will Feel    Return to top

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

Why the Test is Performed    Return to top

The kidneys function as filters for the blood, removing waste products. They also:

Dialysis replaces some of the functions for kidneys that aren't working properly. It removes contaminants from the blood that could, and eventually would, lead to death if the kidney is not functioning.

Since dialysis is not a constant process, it cannot monitor body functions as do normal kidneys, but it can eliminate waste products and restore electrolyte and pH levels on an as-needed basis.

Dialysis is most often used for patients who have kidney failure, but it can also quickly remove drugs or poisons in acute situations. This technique can be lifesaving in people with acute or chronic kidney failure.

Risks    Return to top

The immediate risks include:

Long-term risks include:

Considerations    Return to top

Take the following precautions if you are using an AVF or AVG:

If you have an external access, take these additional precautions:

If you perform peritoneal dialysis at home:

Do not miss or skip any dialysis sessions.

References    Return to top

Tolkoff-Rubin N. Treatment of irreversible renal failure. In: Goldman L, Ausiello D, eds. Cecil Textbook of Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 133.

Mitch WE. Chronic kidney disease. In: Goldman L, Ausiello D, eds. Cecil Textbook of Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 131.

Update Date: 10/15/2008

Updated by: Parul Patel, MD, Private practice specializing in Nephrology, Kidney and Pancreas Transplantation, affiliated with California Pacific Medical Center, Department of Transplantation, San Francisco, CA. Review provided by VeriMed Healthcare Network. Also reviewed byDavid Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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