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Living Day to Day with Kidney Dialysis

How Dialysis Works continued...

Blood drains into the dialysis machine to be cleaned. The machine has two parts, one side for blood and one for a fluid called dialysate. A thin, semipermeable membrane separates the two parts. As dialysate passes on one side of the membrane, and blood on the other, particles of waste from the blood pass through microscopic holes in the membrane and are washed away in the dialysate. Blood cells are too large to go through the membrane and are returned to the body.

The benefits of hemodialysis are that the patient requires no special training, and he or she is monitored regularly by someone trained in providing dialysis.

The other type of treatment, peritoneal dialysis, uses the patient's own peritoneal membrane as a filter. The peritoneal membrane is a sac around the abdominal organs. This membrane (like the dialysis machine membrane) is semipermeable. Waste particles can get through it, but larger blood cells cannot.

The patient has a plastic tube called a peritoneal catheter surgically implanted into the belly. He or she slowly empties about two quarts of dialysate fluid through the catheter into the abdomen. As the patient's blood gets exposed to the dialysate through the peritoneal membrane, impurities in the blood are drawn through the membrane walls and into the dialysate. The patient drains out the dialysate after three or four hours and pours in fresh fluid. The draining takes about half an hour and must be repeated about five times a day. This is called Continuous Ambulatory Peritoneal Dialysis (CAPD).

The main benefit of CAPD is freedom -- the patient doesn't have to stay at a dialysis clinic several hours a day, three times a week. The dialysate can be exchanged in any well-lit, clean place, and the process is not painful. The drawback to this treatment is that some people get an infection of their peritoneal lining, and the process may not work well enough on very large people.

Children often do a similar type of dialysis called Continuous Cycling Peritoneal Dialysis (CCPD). Their treatments can be done at night while they sleep. A machine warms and meters dialysate in and out of their abdomens for 10 hours continuously. Then they are free from treatments during the day.

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