What is dialysis?

To understand dialysis, you need to know about the kidneys and what they do. The kidneys are organs located in the back of your body, just below your ribs. They look like beans and are about the size of a fist. Most people are born with two kidneys, one on each side, but people can live normally with one.

The kidneys do many good things for the body. The main job of the kidneys is to filter the body's blood supply to remove extra water, salt and the waste products left over after the body uses the energy it needs to live. The extra fluid and waste leave the body when you urinate.

Since the body is made up mostly of water, the kidneys make sure there is the right balance of fluid for the body to stay healthy. The kidneys also control blood pressure, maintain the levels of certain chemicals in the blood and make hormones necessary for the body to function correctly.

Each kidney contains about one million tiny structures, called nephrons, along with a series of collecting tubes. This is where the filtering takes place. Sometimes the nephrons start to lose their ability to filter blood. This is most often caused by conditions such as diabetes, high blood pressure, and obesity. These conditions make the kidneys work extra hard, and they start to break down. Most often, damage to the kidneys happens slowly over a period of time.

When the kidneys do not work, the blood must be filtered another way. This is done using a treatment called dialysis. Dialysis does what the kidneys are no longer able to do. There are different types of dialysis. They differ in the way the filtering is done. The main methods of dialysis are hemodialysis and peritoneal dialysis. You and your doctor will discuss which type of dialysis is best for you.

What is hemodialysis?

During hemodialysis, a machine with a special filter (called a dialyzer) is used to clean the blood. The filter is sometimes called an "artificial kidney." The blood flows from the body into the dialyzer where the filtering takes place, and then the clean blood returns to the body. The blood leaves and returns through a small opening called access. The access is made by your doctor during a minor procedure and stays in place between treatments. During treatment, needles are placed into the access to allow the blood to flow in and out.

There are different types of access:

Fistula – This is the most common. To make a fistula, the doctor links an artery directly to a vein, usually in the arm. This allows for more blood to flow into the vein. A fistula can take several months to be ready to use.

Graft – If your veins are small or the fistula doesn't develop properly, the doctor can place a soft hollow tube under your skin to link the artery and vein. A graft is ready to use as soon as the surgical swelling goes down, usually within a week or two.

Venous catheter – Sometimes it is necessary to begin dialysis before the fistula or graft is ready. In these cases, the doctor can place a hollow tube into a larger vein, usually on your neck or shoulder. This access is usually temporary, used until permanent access is developed.

You will be taught how to care for your access.

Hemodialysis can be done in a hospital or in a dialysis clinic. The time it takes for this type of dialysis depends on factors such as how damaged your kidneys are, how big you are, how much extra fluid you have in your body and the type of machine being used. In most cases, treatments last about four hours and are done three times a week. You will also follow a special diet.

What is peritoneal dialysis? How is it different?

Peritoneal dialysis is different because the blood is filtered inside the body, but not through the kidneys.

Peritoneal dialysis enables you to have more freedom because you do not have to go to a dialysis center. You can do this yourself at home and even at work. There are two types of this kind of dialysis: continuous ambulatory peritoneal dialysis (CAPD) and continuous cycling peritoneal dialysis (CCPD).

Continuous ambulatory dialysis — During CAPD, a special fluid, called dialysate, is pumped into the space in your belly – called the peritoneal cavity – through a small opening using a soft tube called a catheter. The dialysate is able to remove the waste products through the blood vessels that line the cavity. The water and wastes are removed when you drain the solution from your body.

The process of filling and emptying the fluid is called an exchange. It usually takes about 30 to 40 minutes to complete. The PD fluid dwells within the abdomen for several hours during an exchange. How often you must do this depends on your condition, but it is generally done four times a day. CAPD does not use a machine, so you can walk around while you are having the treatment.

Continuous cycling peritoneal dialysis — CCPD still uses a machine, called a cycler, which fills and drains the solution from your body. The benefit of this type of dialysis is that you can do it while you are sleeping, which frees up your day for school or work. You usually do CCPD for six to eight hours 5 to 7 times a week.

Why would someone need dialysis?

People whose overall kidney function is so poor that it threatens health and survival are said to have end-stage renal disease (ESRD), and need renal replacement therapy--either dialysis or kidney transplantation. When a kidney transplant is not immediately available or not possible, dialysis can replace the critical functions of the kidneys and sustain life. Today, about 350,000 people in the United States use dialysis as renal replacement therapy.

(This information comes from the National Institute of Diabetes, and Digestive, and Kidney Diseases (NIDDK). To learn more visit the NIDDK website.)

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