The peritoneum is a natural lining or membrane that lines the inside of the abdominal wall and covers all the abdominal organs (the stomach, bowels, liver, etc.). It resembles a sausage skin, but has lots of extremely tiny holes in it. These holes allow the peritoneum to be used for dialysis (clearing waste from the blood). As blood flows through the blood vessels in the peritoneum, it flows past the holes. Although the holes are extremely tiny, water and toxins can easily pass through, but blood cells are too large. In this way the peritoneum in PD works as a ‘natural filter’, performing the same function as the ‘artificial filter’ used in haemodialysis.
The peritoneum has two layers, and the space or cavity between the layers can be used as a reservoir for dialysis fluid. Normally, the peritoneal cavity contains only about 100 ml of liquid. In fact, it can expand to hold up to 5 litres of liquid (Women who have been pregnant can vouch for this).
The basic principles of dialysis are the same for PD and haemodialysis. Both types of dialysis use a special liquid (called the dialysis fluid, dialysis solution or dialysate) and a membrane (called the dialysis membrane) to do some of the work of the kidneys. In PD, the dialysis membrane is the person’s own peritoneum (see diagram right). The dialysis fluid provides the ‘container’ in which waste products and excess water can be removed from the body. The dialysis membrane acts as a filter. It keeps the dialysis fluid and the blood separate from each other, but it allows certain substances and water to pass through it. During dialysis, waste toxins and excess water pass from the blood into the dialysis fluid, and this is drained out of the body after a few hours. A new bag of dialysis fluid is drained in, and the process is repeated.
PD needs to be done every day. PD involves draining dialysis fluid out of, and into the body (known as an exchange), and leaving dialysis fluid in the body while dialysis takes place. Draining fluid out usually takes around 20 minutes and draining fluid in takes around 5-10 minutes.
There are no ‘set’ times to carry out the exchanges. However, on CAPD, a four-bag regime ‘fits’ into a typical day. For example, the first bag might be exchanged before breakfast, the second before lunch, the third before the evening meal, and the fourth before going to bed (leaving the fluid for the last exchange in through the night). It is easy for people to adapt the timing of exchanges to their own needs. For example, if a person wants to go out for the day, they could delay the mid-day exchange, and do two ‘quick bags’ (say, 3 hours apart) after they come home. See diagram below.
Joanne, a CAPD patient, has kindly agreed to show us how to carry out a CAPD exchange. This is presented on a series of 15 webpages – a bit like a slide show. Each picture has a brief caption explaining what is being shown. For more information on CAPD, click on the ‘Peritoneal Dialysis’ button on the left.
Click here to move to the first picture, then click on the 
button on each page to continue through the show.
To receive PD, a kidney patient first needs to have an operation. During the operation (which is performed using a local or a general anaesthetic), a plastic tube is permanently inserted into the abdomen (see diagram). This tube is called a PD catheter. It is about 30 cm (12 in) long and as wide as a pencil.
The PD catheter is placed through the lower abdominal wall, into the peritoneal cavity. Half of the catheter lies inside the abdomen, and half lies outside the body. It comes out to one side of the navel (belly button). The PD catheter acts as a permanent pathway into the peritoneal cavity from outside the body.
People are usually allowed to go home 1 or 2 days after the operation to insert their PD catheter. The catheter is usually ‘left alone’ for 5 days or more after the operation before it is used for dialysis. This allows it to ‘settle in’ and gives the abdominal wound time to heal. Some people remain in hospital while they train to do their PD exchanges, but most go to the hospital each day for training.
Before anyone is expected to carry out their own dialysis, specialist nurses will train them in all aspects of their care. Most people can become competent in the exchange technique in 3 to 14 days. Some hospitals train people as an in-patient, some as an out-patient. When people first go home and have to do the exchanges by themselves, they may find it a bit daunting. However, within a few weeks most people find that they are doing the dialysis by themselves without any problems. All Units can give advice 24 hours a day, and people on PD need to know who to contact their Unit if they have a problem.
PD is performed by people in their own homes. They therefore need to have supplies of fluid delivered to them and to be able to store these supplies in a convenient place. The bags of dialysis fluid come in boxes. Each box contains four or five bags of fluid. One month’s supplies can be as many as forty boxes. These can be stored in a cupboard under the stairs, a spare bedroom, the shed or even the garage.
Most people receive a delivery of supplies once a month, though people with very small houses or flats may be able to arrange fortnightly deliveries. The people who deliver the supplies deliver to many others on dialysis, and are specially recruited and trained to go into peoples’ homes. They will move the supplies to exactly where people want them, and will even move boxes around so that fluid from previous deliveries gets used before the new stock. Many people don’t like the idea of a ‘delivery man’ coming to their home regularly, but may find the relationship with their driver is positive, and part of the overall security you need when doing your own dialysis.
NKF Controlled Document No. 220, What is Peritoneal Dialysis?, written 26 January 2001. Last reviewed 1 November 2007.
The National Kidney Federation cannot accept responsibility for information provided. The above is for guidance only. Patients are advised to seek further information from their own doctor.
Page created: 26 January 2001
Last updated: 22 August 2007
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