American Medical Association Family Medical Guide - American Medical Association [543]
Dialysis
If your kidneys are temporarily unable to function, or if they have been badly damaged by chronic inflammation, you will probably receive a treatment called dialysis. In dialysis, the functions of the kidneys, which include removing waste products from the body and regulating the body’s chemical and water balance, are performed by a machine called a dialysis unit or by infusing a special fluid into the abdomen.
There are two forms of dialysis—hemodialysis (usually called, simply, dialysis) and peritoneal dialysis. Hemodialysis filters waste products from the blood. To do this, blood from an arm or leg artery is passed through a thin tube to the dialysis unit, through its filter, and back through another tube into an adjacent vein. A special solution in the filter draws out waste, and suction draws out excess fluid. A standard hemodialysis treatment lasts 4 hours and is repeated two or three times a week, which is enough to control the levels of waste products and excess water in the body.
How hemodialysis is done
In hemodialysis, blood from an artery in your arm or leg flows through a tube and into a machine called a dialysis unit. Inside the dialysis unit, a membrane filter that works as an artificial kidney cleanses the blood, which then flows out of the machine and back into your body through another tube, which has been inserted into a vein in the same arm or leg.
Before beginning dialysis treatment, you must first have a minor surgical procedure in which an artery and a vein in your arm are connected to enlarge the vein and provide permanent access to your bloodstream for hemodialysis. If your veins are too small for this procedure, a synthetic blood vessel is placed under your skin to connect an artery and a vein. Temporary dialysis is performed using a thin, flexible tube (catheter) placed in a large blood vessel. People on dialysis learn how to insert their own needles and run the machine themselves. Small portable dialysis units are available that allow people on home dialysis to travel and take their machine with them. People who receive a kidney transplant (see page 820) no longer need dialysis.
In peritoneal dialysis, the doctor makes a small incision in your abdominal wall and threads a thin plastic tube into your abdomen. A special fluid flows slowly through the tube and fills the peritoneal space (the space between the inner and outer layers of the lining of the abdomen). The fluid draws in waste products from the blood vessels that line the abdomen, and drains from the abdomen along with excess water. The process takes several hours. Peritoneal dialysis is a painless procedure.
If you have acute kidney failure, you will gradually be weaned off of dialysis as your kidneys recover. If the damage to your kidneys is permanent, you may be taught to perform peritoneal dialysis yourself. This procedure (called continuous ambulatory peritoneal dialysis, or CAPD) is performed at home, during the day or overnight, and allows you to carry out your normal daily activities.
In chronic kidney failure, body chemicals gradually build up in the blood, and the kidneys gradually lose their ability to filter and excrete waste products and excess water. Because the kidneys also help regulate blood pressure, chronic kidney failure can cause high blood pressure (see page 574). The kidneys can become scarred and continue to lose function, which eventually leads to end-stage