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Dialysis dī-ˈal-ə-səs

by James I. McMillan, MD

Dialysis is an artificial process for removing waste products and excess fluids from the body, a process that is needed when the kidneys are not functioning properly.

There are a number of reasons why people may need dialysis, but the inability of the kidneys to adequately filter waste products from the blood (kidney failure) is the most common. Kidney function may decline quickly (called acute kidney injury or acute kidney failure—see Acute Kidney Injury), or the kidneys may slowly lose their ability to filter waste products (called chronic kidney disease or chronic kidney failure—see Chronic Kidney Disease). In people with kidney failure, many doctors recommend dialysis when blood tests show that the kidneys can no longer filter waste products adequately and the accumulating waste products cause problems. For acute kidney injury, doctors continue dialysis until the person’s blood test results indicate that adequate kidney function has been restored. For people with chronic kidney disease, dialysis may be used as long-term therapy or as a temporary measure until a kidney can be transplanted. Short-term or urgent dialysis can also be used to remove fluids, certain drugs, or poisons from the body.

Making the decision to begin long-term dialysis is not easy because it entails a major change in lifestyle, including a dependency on machines to maintain life. However, for most people, a successful dialysis program results in an acceptable quality of life. Most people undergoing dialysis are able to eat a tolerable diet, have normal blood pressure, and avoid progression of nerve damage, severe anemia (a decrease in the number of red blood cells, which carry oxygen to the cells of the body), and other severe complications.

Dialysis usually requires the effort of a team of people. A doctor completes a dialysis prescription, manages complications, and provides the medical care. A nurse monitors the person’s general well-being, educates the person about dialysis and what needs to be done to maintain the best possible health, oversees the dialysis procedure, and supervises the dialysis technicians. Often, a social worker assesses mental health, arranges transportation, arranges for dialysis in other locations if the person is traveling, and arranges home assistance when needed. A dietitian recommends an appropriate diet and monitors the person’s response to dietary changes. When dialysis is intended to be used temporarily until a kidney can be transplanted, the transplant surgeon is also part of the dialysis team. For hemodialysis (in which blood is removed from the body and filtered by an artificial kidney machine), a technician assists in getting the procedure started and monitors the dialysis machine during the dialysis. For hemodialysis, doctors such as a vascular surgeon and often an interventional radiologist prepare the blood vessels so that blood can be easily withdrawn from the body and cycled through the dialysis machine.

Occasionally, another technique (such as hemofiltration or hemoperfusion) is used to temporarily filter the blood and accomplish what dialysis would. These techniques are most often used if dialysis cannot be done, to remove the poisons from the blood, or to remove large amounts of fluid in some people who have acute kidney injury.

Types of Dialysis

There are two types of dialysis:

  • Hemodialysis

  • Peritoneal dialysis

Hemodialysis

In hemodialysis, blood is removed from the body and pumped by a machine outside the body into a dialyzer (artificial kidney). The dialyzer filters metabolic waste products from the blood and then returns the purified blood to the person. The total amount of fluid returned can be adjusted.

Hemodialysis requires repeated access to the bloodstream. Doctors can achieve temporary access by inserting a large intravenous catheter in a big vein, usually one near the neck. However, an artificial connection between an artery and a vein (an arteriovenous fistula) is usually surgically created to make long-term access easier. In this procedure, typically the radial artery in the forearm is joined with the cephalic vein in the forearm. As a result, the cephalic vein subsequently enlarges and blood flow through the vein increases, making the vein suitable for repeated puncture with a needle. Fistulas are created by vascular surgeons. When a fistula cannot be created, an artery and a vein may be surgically connected to each other using a synthetic connector (graft). Grafts are often placed in the person's arm. In hemodialysis, a technician places needles into the person's fistula or graft.

Heparin, a drug that prevents clotting, is given during hemodialysis to prevent blood from clotting in the dialyzer. Inside the dialyzer, a porous artificial membrane separates the blood from a fluid (the dialysate). Fluid, waste products, and electrolytes in the blood filter through the membrane into the dialysate. Blood cells and large proteins are unable to filter through the small pores of the membrane and so remain in the blood. The dialyzed (purified) blood is then returned to the person’s body.

Dialyzers have different sizes and degrees of efficiency. Dialysis treatment time is usually about 3 to 5 hours. Most people who have chronic kidney disease need hemodialysis 3 times a week.

The most common complication of hemodialysis is low blood pressure during or shortly after dialysis. Blood pressure usually increases during the period between treatments. People, particularly when starting hemodialysis, may have muscle cramps, itching, nausea and vomiting, headache, restless legs syndrome, and pain the chest and back. Less often, they can have confusion, restlessness, blurred vision, and/or seizures.

Complications can also involve the graft or fistula, such as infection, blood clots, bleeding, and bulging (aneurysm formation). People should promptly notify their doctors if any of the following occur:

  • Pain

  • Redness or warmth

  • Breaks in nearby skin

  • Bruising

  • Prolonged bleeding from the fistula site

  • Rapidly enlarging (over a few days or less) bulge over the graft or fistula

  • Loss of the pulse or vibratory feeling that the graft or fistula site normally has

  • Swelling (edema)

Some Common Complications of Hemodialysis

Complication

Usual Cause

Fever

Bacteria or fever-causing substances (pyrogens) in the bloodstream

Overheated dialysate

Life-threatening allergic reaction (anaphylaxis)

Allergy to a substance in the dialyzer or the tubing that carries blood or to drugs given during dialysis

Low blood pressure

Removal of too much fluid

Abnormal heart rhythms

Abnormal levels of potassium and other substances in the blood

Low blood pressure

Air embolus

Air entering the tubing that carries blood

Bleeding in the intestine, brain, eyes, or abdomen

Use of too much heparin to prevent clotting in the dialyzer

Infection

Bacteria entering the bloodstream through a needle inserted into veins for hemodialysis access

Muscle cramps

Possibly rapid changes in the amount or distribution of body fluids or salts

Peritoneal dialysis

In peritoneal dialysis, the peritoneum—a membrane that lines the abdomen and covers the abdominal organs—acts as a filter. This membrane has a large surface area and a rich network of blood vessels. Substances from the blood can easily pass through the peritoneum into the abdominal (peritoneal) cavity. A fluid (dialysate) is infused through a catheter inserted through the abdominal wall into the peritoneal space within the abdomen. The dialysate must be left in the abdomen for a sufficient time to allow waste products from the bloodstream to pass slowly into it. Then the dialysate is drained out, discarded, and replaced with fresh dialysate.

A soft silicone rubber or porous polyurethane catheter allows the dialysate to flow smoothly and is unlikely to cause damage. A catheter can be put in place temporarily at the person’s bedside, or it may be surgically put in place permanently. One type of permanent catheter eventually forms a seal with the skin and can be capped when not in use.

Peritoneal dialysis can be done using a machine (called automated peritoneal dialysis) or without one (called manual techniques).

Manual peritoneal dialysis techniques are the simplest. No machine is used. There are two types:

  • In manual intermittent peritoneal dialysis, bags containing dialysate are warmed to body temperature and infused into the peritoneal (abdominal) cavity, which takes about 10 minutes. The dialysate is allowed to remain there (dwell time) for 60 to 90 minutes and then is drained out in about 10 to 20 minutes. This process is then repeated. The entire treatment can take 12 to 24 hours. Between periods of dialysis, there is no dialysate in the peritoneal cavity.

  • In continuous ambulatory peritoneal dialysis, the dialysate is usually drained and replenished 4 or 5 times per day. Generally, 3 of these dialysate exchanges are done during the day, with dwell times of 4 hours or longer. An exchange is done at night with a long dwell time of 8 to 12 hours during sleep. Continuous ambulatory peritoneal dialysis differs from intermittent peritoneal dialysis in that there is always dialysate in the peritoneal cavity.

Automated peritoneal dialysis techniques are becoming the most commonly used forms of peritoneal dialysis. In automated peritoneal dialysis, an automated device does multiple exchanges during the night while the person sleeps. These techniques minimize the number of exchanges during the day but prevent mobility at night because of cumbersome equipment. Sometimes a daytime exchange time is used. Automated peritoneal dialysis techniques are further divided into three subcategories:

  • Continuous cyclic peritoneal dialysis uses a long (12- to 15-hour) daytime dwell period and 3 to 6 nighttime exchanges done with an automated cycler.

  • Nocturnal intermittent peritoneal dialysis uses exchanges done with a cycler at night while the person's peritoneal cavity is left without dialysate fluid during the day.

  • Tidal peritoneal dialysis is a modification in which some of the dialysate fluid is left in the peritoneal cavity from one exchange to the next. This technique may be more comfortable for the person. Tidal peritoneal dialysis may be done with or without a daytime dwell period.

Some people require a combination of continuous ambulatory peritoneal dialysis and continuous cyclic peritoneal dialysis to achieve adequate removal of waste products from their blood.

Choice of technique

Many factors, including lifestyle, must be considered in determining which type of dialysis is best for a person. People typically undergo hemodialysis at a dialysis center, usually outside of a hospital. Peritoneal dialysis can be done at home, eliminating the need for travel to a hemodialysis center.

Doctors recommend hemodialysis for people with recent abdominal wounds or abdominal surgery or defects in the abdominal wall that make peritoneal dialysis difficult. Peritoneal dialysis is better tolerated in people whose blood pressure fluctuates frequently between periods of high or normal pressure and periods of low blood pressure.

Some Common Complications of Peritoneal Dialysis

Complication

Cause

Low blood pressure

Loss of too much fluid and salt during dialysis

Bleeding

Unintentional perforation of an internal organ during placement of the catheter

Removal of the catheter from the body

Irritation and inflammation of the membrane that lines the abdomen (peritoneum) or the area around the insertion site (when the catheter does not seal to the abdominal wall)

Infection

Unsterile techniques during dialysis

Low level of albumin (a protein) in the blood

Loss of protein in fluid removed during dialysis along with inadequate protein in diet

Scarring of the peritoneum*

Inflammation and infection

Electrolytes in the dialysis fluid

Use of certain drugs

A high sugar (glucose) level in the blood

Use of a peritoneal dialysate that has a high concentration of glucose (used to remove water and sodium during dialysis)

Hernias in the abdomen or groin

Increased pressure within the abdomen caused by continued exposure to high fluid levels, which weaken the barriers that normally prevent excessive movement of organs and other structures

Constipation

Intake of inadequate fiber or use of calcium salts to treat high phosphate levels in the blood, causing the intestine to widen, which possibly interferes with dialysate flow in and out of the abdomen

*The peritoneum acts as a filter in peritoneal dialysis. When the peritoneum is scarred, fluids and waste products can no longer readily pass through it to be removed.

The most common and troublesome complications of peritoneal dialysis are infection of the peritoneal fluid (causing inflammation of the peritoneum, called peritonitis) and infection of the area where the catheter enters the skin (insertion site). Peritonitis may cause constant, sharp, severe pain throughout the abdomen, but sometimes causes little pain. Infection at the insertion site causes redness of the skin and pain at the insertion site. Such infections can be treated with antibiotics and careful wound care.

Comparing Hemodialysis With Peritoneal Dialysis

When the kidneys fail, waste products and excess water can be removed from the blood by hemodialysis or peritoneal dialysis.

In hemodialysis, blood is removed from the body into a dialyzer (called an artificial kidney), which filters the blood. An artificial connection between an artery and a vein (arteriovenous fistula) is made to facilitate the removal of blood.

In peritoneal dialysis, the peritoneum is used as a filter. The peritoneum is a membrane that lines the abdomen and covers the abdominal organs, creating a space within the abdomen called the peritoneal space or abdominal cavity. Waste products from the body drain across the peritoneum into the fluid (dialysate) in the abdominal cavity.

Special Considerations

Diet

People undergoing dialysis need a special diet. In people undergoing peritoneal dialysis, appetite is generally poor, and protein is lost during dialysis. The diet should have enough calories (about 16 calories per pound of ideal body weight, slightly more in children) and be relatively high in protein (about 1/2 gram of protein per pound of ideal body weight) per day). ( The American Association of Kidney Patients has a food guide.) Salt, both the usual table salt containing sodium and the salt containing potassium, is restricted.

For people undergoing hemodialysis, daily consumption of sodium and potassium is even more restricted. Foods high in phosphorus also may have to be limited. Daily fluid intake is limited for people who have very little urine output or a persistently low or decreasing sodium concentration in the blood. Daily weighing is important to monitor weight gain. Excessive weight gain between hemodialysis treatments indicates that the person is consuming excessive fluid. Usually, excessive fluid intake is the result of excessive sodium intake, which makes a person thirsty.

Multivitamin supplements are needed to replace the nutrients lost through hemodialysis or peritoneal dialysis. Vitamin supplements should be discussed with a doctor or nutritionist.

Medical considerations

Because people with chronic kidney disease develop anemia, erythropoietin or darbepoietin may be given to stimulate the production of red blood cells. Iron may also be needed to help the body produce new red blood cells.

Phosphate binders, most often those such as calcium carbonate or calcium acetate, are used to remove excess dietary phosphate.

Normally the body’s bone tissue is continually replaced, helping bones remain strong and dense. The kidneys convert vitamin D to its active form ( calcitriol ), which helps regulate the amount of calcium in the blood and the amount used to produce bone tissue. In people with kidney failure, the kidneys are not able to convert enough vitamin D to its active form, so parathyroid hormone levels may increase. High parathyroid hormone levels can weaken bones by decreasing their density, a bone condition called renal osteodystrophy (see Chronic Kidney Disease). To correct this problem, the active form of vitamin D or a similar substance is given to lower high parathyroid hormone levels..

People who are undergoing dialysis often have risk factors for coronary artery disease, including high blood pressure, high levels of lipids (fats) in the blood, and diabetes. People need to take special care to lower their risk of coronary artery disease.

Constipation may occur in people undergoing dialysis, which may hamper peritoneal dialysis. If too much stool fills the intestine, the extra volume can partly block the catheter that drains dialysis fluid. People may need to take laxatives, but they are usually given bulking agents (such as psyllium) or sorbitol, not laxatives that contain phosphate or magnesium (see Laxatives).

High levels of aluminum in the blood (aluminum toxicity) may occur in people who take phosphate binders that contain aluminum. Another potential source of aluminum is the water used to make the dialysate. Because many phosphate binders are available that do not have aluminum and because aluminum is effectively removed during preparation of the ultra pure water used in dialysate today, aluminum toxicity is now uncommon. Aluminum toxicity can cause weak bones, anemia, and dementia. Deferoxamine can be given through the peritoneal catheter or through a vein to help eliminate aluminum from the body.

Calciphylaxis is a rare disorder in which arteries harden, causing a reduction in blood flow to the skin of the trunk, buttocks, and legs. It is caused in part by high levels of calcium and phosphorus in the blood. It causes painful skin bumps and ulcers that often become infected. Severe infection can affect the entire body and be fatal. Treatment aims to relieve complications of calciphylaxis. For example, infection is treated with antibiotics, and pain is treated with analgesics. Drugs may be given to lower levels of calcium and phosphorus in the blood. Wounds are treated with careful skin care.

Psychosocial considerations

People undergoing dialysis may experience losses in every aspect of their life. The potential loss of independence can be especially distressing. Coping with disruptions in lifestyle can be difficult. Many people undergoing dialysis become depressed and anxious. Psychologic and social counseling is often helpful to families as well as to those undergoing dialysis. Many dialysis centers provide psychologic and social support. Dealing with a loss of independence is helped when people are encouraged to pursue their previous interests. People undergoing hemodialysis need to arrange for transportation to and from dialysis centers on a regular basis. Dialysis sessions may interfere with work, school, or leisure activities.

More than half of the people on long-term dialysis are 60 years of age or older. Older people often are better able to adapt to long-term dialysis and the loss of independence than are younger people. However, older people undergoing dialysis may become more dependent on their grown children or may not be able to continue living alone. Older people are more likely to experience fatigue from treatments. Often, family roles and responsibilities must be modified to fit the dialysis routine, creating stress and feelings of guilt and inadequacy.

Considerations in children

Children whose growth has been stunted may feel isolated and different from their peers. Young adults and adolescents coping with identity, independence, and body image issues may find these issues further complicated by dialysis. Diet is an important issue for children undergoing dialysis because children must receive enough nutrients to support their growth.

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