ADAM Health Encyclopedia

Dialysis

Definition

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

Alternative Names

Why the Test is Performed

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

• Regulate body water
• Maintain electrolyte balance
• Ensure that the blood pH remains between 7.35 and 7.45

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 life saving in people with acute or chronic kidney failure.

How the Test is Performed

Dialysis can be performed using several different methods.

PERITONEAL DIALYSIS

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

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).

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

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:

• Blood pressure
• Breathing rate
• Chest assessment
• Examination of venous access
• Heart rate
• Temperature
• Weight

How the Test Will Feel

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

Risks

The immediate risks include:

• A small bubble of air in the blood that travels to a blood vessel in another part of the body (air embolism)
• Bleeding from the access site
• Cramps
• Dialyzer reaction
• Electrolyte imbalance
• Infection
• Irregular heartbeat or ischemia
• Low blood pressure (hypotension)
• Nausea and vomiting

Long-term risks include:

• Autonomic neuropathy
• Blood loss leading to iron deficiency
• Cardiovascular disease
• Dialysis-associated amyloidosis
• Dialysis dementia

Considerations

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

• Do not allow anyone to take a blood pressure reading on an arm with the access.
• Do not use creams or lotions over the access site.
• Do not wear tight clothing around the access site.
• Observe the access site after dialysis, watching for swelling, infection, or bleeding.
• 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.)
• When you sleep, avoid placing pressure on an arm with the access (if the graft or fistula clots, you may need a new one).

• 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.)
• Call your health care provider immediately if you have a fever or other sign of infection.
• If the color in the tubes changes and becomes a dark red, call your health care provider immediately. (The blood may be clotting.)

If you perform peritoneal dialysis at home:

• Report any fever immediately.
• Report any pain in your abdomen immediately.

Do not miss or skip any dialysis sessions.