Peritoneal Dialysis: How Does It Work?

Peritoneal dialysis is another procedure that removes extra water, wastes and chemicals from your body. This type of dialysis uses the peritoneum inside your abdomen as a filter membrane ("dialyser"). The peritoneum is a thin lining (membrane) that covers the inner wall of the abdominal cavity as well as most of your abdominal organs. The peritoneal membrane contains many tiny blood vessels and has a large adjoining surface to the abdominal cavity. Therefore, it is appropriate to filter your blood, when your abdominal cavity is filled with a clean dialysis fluid.

The dialysis fluid is put into your abdomen through a small soft tube, e.g. a Tenckhoff catheter. This solution contains a mixture of minerals and sugar dissolved in water. The sugar, called dextrose, draws wastes, chemicals and extra water from the blood vessels in your peritoneal membrane into the dialysis solution. After a few hours, the used solution is drained from your abdomen through the soft tube, taking the wastes from your blood with it. The period during which the dialysis solution is in your abdomen is called the dwell time. Then you fill your abdomen with fresh dialysis solution and the cycle is repeated. Each cycle is called an exchange and has to be performed 4 to 5 times per day. Patients can perform peritoneal dialysis by themselves.

Principle of Continuous Ambulatory Peritoneal Dialysis (CAPD)

Types of peritoneal dialysis

There are two main types of peritoneal dialysis: the Continuous Ambulatory Peritoneal Dialysis (CAPD), typically done during the day and the Continuous Cycling Peritoneal Dialysis (CCPD) that can be performed at night by using a machine that drains and refills the abdomen automatically. Both types of peritoneal dialysis are usually performed by the patient without help from a partner.

1. Continuous Ambulatory Peritoneal Dialysis (CAPD)

CAPD is the most common type of peritoneal dialysis. It requires no machine and can be done while you go about your daily life. With CAPD, your blood is being cleaned continuously. The dialysis solution passes from a plastic bag through the catheter and into your abdomen, where it stays for several hours while the catheter is sealed. Next, you drain the dialysis solution back into the bag for disposal. You then use the same catheter to refill your abdomen with fresh dialysis solution so the cleaning process can begin again. With CAPD, the dialysis solution stays in your abdomen for a dwell time of 4 to 6 hours (or more). The process of draining the used dialysis solution and replacing it with fresh solution takes about 30 to 40 minutes. It should be done in a clean, well-lit place. Most people change the dialysis solution at least four times a day and sleep with the solution in their abdomen at night. With CAPD, it’s not necessary to wake up and perform dialysis tasks during the night.

2. Continuous Cycling Peritoneal Dialysis (CCPD)

CCPD is also called Automated Peritoneal Dialysis (APD). It uses a machine called a cycler to fill and empty your abdomen three to five times during the night while you sleep. In the morning, you begin one exchange with a dwell time that lasts the entire day. During that time you are free to go about your daily activities. Before going to bed, the catheter will be re-attached to the cycler and the night exchanges are started.

A modified form of CCPD is the “PD Plus-therapy” that requires one additional exchange during the day. This type is mainly used by larger/overweight patients or if the peritoneal membrane filters wastes slowly. If PD Plus-therapy is advised by your doctor, you can use a cycler at night but also perform one exchange during the day. At that time the cycler can be used as source of dialysis fluid – if you are at home, or you can use the CAPD method. This additional exchange is implemented to increase the amount of waste removed and to reduce the amount of fluid left behind in your body.

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  1. Schönweiß G: Dialysefibel 3, Band 2. Abakiss Verlag, 3rd Edition, 2006.