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Alternative names

Artificial kidneys; Hemodialysis; Peritoneal dialysis; Renal replacement therapy;


Dialysis is a method of removing toxic substances (impurities or wastes) from the blood when the kidneys are unable to do so. Dialysis is most frequently used for patients who have kidney failure , but may also be used to quickly remove drugs or poisons in acute situations. This technique can be life saving in people with acute or chronic kidney failure .

How the test is performed

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 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.

How to prepare for the test

Blood pressure medications are frequently withheld 6 to 12 hours before hemodialysis, as are water soluble vitamins.

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 a 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.

What the risks are

Immediate risks include:
  • Shock
  • Emotional distress
  • Infection
  • Electrolyte imbalance
Long term risks include:
  • Anemia
  • Hypotension
  • Growth retardation
  • Neurologic complications
  • Pericarditis
  • Osteodystrophy
  • Severe psychological problems
  • Peritonitis (for peritoneal dialysis)
  • Peritonitis; dialysis associated

Special considerations

Take the following precautions if you have internal angioaccess (access to a vein through a fistula or AV Graft):
  • When you sleep, avoid placing pressure on the extremity with the access
  • Do not allow anyone to take a blood pressure on the extremity with the access
  • Observe the access site after dialysis watching for swelling , infection, or bleeding
  • Do not wear tight clothing around the access site
  • Routinely check the access site for the thrill indicating that the AV site is still functioning (if the thrill disappears, call your health care provider immediately)
  • Do not use creams or lotions over the access site
If you have an external access, take additional precautions:
  • Avoid physical activity that might dislodge the access, which could result in excessive bleeding, and air entering the circulatory system (if this happens, call 911 and get immediate medical attention)
  • If the color in the tubes changes color and becomes a dark red, call your health care provider immediately (the blood may be clotting)
  • Always keep a clamping tool on hand -- in the event that the tubing comes unclamped, you can use the tool to clamp off the tube and stop the bleeding (if this happens call your health care provider immediately)
  • Call your health care provider immediately if your have a fever or other sign of infection
  • Do not allow the site to become wet (protect it with plastic if you are to bathe)

Update Date: 1/20/2002

Andrew Koren, M.D., Department of Nephrology, NYU-Mount Sinai Medical Center, New York, NY. Review provided by VeriMed Healthcare Network.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT