Using the Kidney you never thought you had

Note: This page is online only because I could not find a layperson's reference to peritoneal dialysis. Please check with your doctor for accurate information on this or any other medical need.

You mean I've got another kidney?

In reality man has only two kidneys. But there is a natural membrane called the peritoneum (perry-toe-knee-um) inside your body that with a special fluid called dialysate can function very much like a kidney does when it removes wastes and water from the blood. If you have been a cycling peritoneal dialysis patient, you may know about it already. But if you have been only on hemodialysis or are completely unfamiliar with dialysis, you will need to know more about another common form of dialysis called Continuous Ambulatory Peritoneal Dialysis (CAPD).

This booklet will help explain what CAPD is all about, and some of the things you and your family will have to learn to take advantage of the freedom CAPD has to offer. CAPD is a technique that requires a little patience and a little practice. However, with the little time you spend to learn a few simple procedures, your blood will be cleansed continuously so that you can enjoy more of the life you want to live without having to be periodically attached to a kidney machine.

What does a normal kidney
do that CAPD can accomplish?

The healthy human kidney helps to control blood pressure, helps to regulate red blood cell production, and helps to regulate the amount of certain elements like sodium, potassium, and calcium found in the blood. The kidney also regulates fluid balance by removing excess water and acts as an elaborate filter to remove unwanted substances from the blood. These substances, dissolved in the excess water, are collected in the bladder and form urine. This is the function of the kidney that the peritoneum can take over with a little help from you.

Why does the kidney stop working?

Sometimes, due to disease or physical damage, the kidney becomes unable to function. This is known as renal failure. When renal failure is permanent and gets progressively worse, it is known as chronic renal failure. Substances that are harmful to the body, and are normally removed by the kidneys, build up and may make the patient feel sick. The patient can become anemic, lose appetite and lose weight, or build up excess fluid and gain weight. The patient can also experience a rise in blood pressure. Sometimes, there will be a noticeable swelling of the ankles and abdomen, and other symptoms may appear.

What are my alternatives?

There are several ways of making up for loss of normal kidney function with respect to the elimination of waste materials and excess fluid. These are: 1) Kidney Transplant, 2) Hemodialysis, 3) Cycling Peritoneal Dialysis or 4) Continuous Ambulatory Peritoneal Dialysis.

A successful kidney transplant is a wonderful thing if a patient is eligible for one and if a transplant kidney becomes available. If not, one of the other alternatives must be considered. In hemodialysis, the blood-cleansing process is performed outside the body by diverting blood from the arteries and veins and filtering it through an artificial kidney machine (hemodialysis machine). Blood flows through the artificial kidney machine where impurities are removed by an artificial membrane filter and the blood flows back into the body.

What is peritoneal dialysis?

Peritoneal dialysis is another way of filtering the blood, but it does this inside the body without diverting the blood from its normal circulation. There are two types of peritoneal dialysis: Continuous Cycling Peritoneal Dialysis (CCPD) and Continuous Ambulatory Peritoneal Dialysis (CAPD). Both use the peritoneum, a thin membrane inside your body that surrounds and helps protect many of your internal organs. Like all other tissues in the body, it has its own blood supply. The process of peritoneal dialysis uses this natural membrane to filter the impurities from the blood in much the same way as hemodialysis does. All the filtering of the blood is done inside the body, so there is no need to connect to a hemodialysis machine.

Continuous Cycling Peritoneal Dialysis requires the use of a peritoneal dialysis machine, often called a cycler. Portable cyclers are available, and CCPD can be done conveniently in your home.

With CAPD, no dialysis machine is required. Dialysis is occurring continuously... as you walk, sit, stand, work, play, whatever is needed. But before we can talk about continuos ambulatory peritoneal dialysis specifically, we have to know something about why and how it works.

CAPD sounds great...
how does it work?

CAPD takes advantage of two scientific principles called Diffusion and Osmosis. Both are concerned with the way a fluid on one side of a membrane reacts with the fluid on the other side of a membrane. Not just any membrane, however, will work. It has to be a semipermeable membrane.

A semipermeable membrane has tiny, microscopic holes or pores that allow very small particles or molecules in the liquid on one side of the membrane to pass through or "permeate" to another liquid on the other side of the membrane - without allowing particles larger than the holes in the membrane to pass through. The artificial kidney or hemodialysis machine previously mentioned contains such a membrane.

The peritoneum is another, natural semipermeable membrane inside the body. It can work much like the kidney does by filtering impurities and excess water from the blood that flows through it.


Diffusion is the process in which particles in two different solutions pass through a semipermeable membrane until there is the same number of particles of any given kind on both sides of the membrane. When these particles are the waste substances usually filtered from the bloodstream by a normal kidney, the waste particles go through the membrane from the blood and into a special solution, called dialysis solution or dialysate, that is placed inside your peritoneal cavity (more about this later). This dialysis solution is changed periodically to maintain a lower concentration of waste products in the dialysis solution than in the blood. This enables diffusion (from blood to dialysis solution) to continue to take place, cleansing the blood of impurities. Since blood cells are relatively large particles, they will not pass through the peritoneal membrane.


We not only want to cleanse impurities from the blood during dialysis, we also want to be able to remove excess water, since this is one of the normal functions of a healthy kidney. Osmosis is the process, much like diffusion, by which water molecules pass through a semipermeable membrane from a solution with a lot of water to a solution with less water until there is the same amount of water on both sides of the membrane. Because dialysis solution contains sugar or dextrose in water, it can have less water in it than there is in the blood. Thus, excess water in the blood will pass to the dialysis solution by the process of osmosis.

Osmosis and diffusion are two important processes that enable peritoneal dialysis to remove impurities and excess water from the blood much like a normal kidney would do. The peritoneum is a semipermeable membrane with blood flowing through it. To make osmosis and diffusion work across the peritoneum, dialysis solution is introduced into the abdominal cavity through a small tube or catheter. Then the cleansing of your blood can begin without your ever being aware that anything is going on.

OK, CAPD... what next?

Continuous Ambulatory Peritoneal Dialysis is a long name for a relatively simple procedure. If you are a hemodialysis patient, CAPD means fewer visits to the dialysis center and no more sitting for several hours during the dialysis procedure.

There will be no more shunts or fistulas, no more worries about being far away from the kidney machine. You will enjoy fewer restrictions on fluid intake and diet.

Yet, for all this new-found freedom, you now hold the responsibility for the supervision of your own daily therapy. Your dialysis center will instruct you thoroughly about the necessary procedure and you will receive detailed manuals describing every step. Be sure to study these carefully and never skip a step for the sake of a short-cut. Sterility and cleanliness are very important in peritoneal dialysis, and if you take short-cuts, serious infection can result. The likelihood of this happening will be less if you follow the procedure carefully and exactly.

How do I begin CAPD?

The first thing you need is a small tube or catheter inserted into your abdomen near your navel. This requires a minor surgical procedure and a short hospital stay. A tiny incision is made and the catheter is placed into your abdominal cavity inside the peritoneum. Once it's in, you will find it easy to live with.

It is through this small tube that the dialysis solution (remember ... osmosis, diffusion?) will be introduced into your abdominal cavity so that it can come into contact with the peritoneum.

If you are a new peritoneal dialysis patient, you will probably use small amounts of dialysis solution in the beginning in order to become used to the volume of fluid in your abdomen.

Once you are ready for CAPD, the dialysis solution will stay in your abdomen about four to six hours, then will be drained out. The process of draining and filling your abdomen with dialysis solution is called making an "exchange". Between exchanges, the dialysis solution is doing its work with your peritoneum, cleansing your blood.

The exciting result is that you are being continuously dialyzed as you move, travel. work, watch a movie ... even go fishing!

That is the whole procedure ... no bloodlines, no nurses, no fancy machinery. Just a little fluid working within your own body.

What about changing the dialysis solution?

This is where you really come in. You change the dialysis solution all by yourself. This may sound scary, but it really should not be. If you have ever been on hemodialysis, you may be saying to yourself, "How can I possibly do what all those nurses and machines take so many hours to do?" The answer is simple. You do not have to do all those things. The machinery and staff are geared to do only one thing ... to place your blood in contact with the dialysis solution or dialysate inside an artificial kidney-outside your body, so that osmosis and diffusion can take place. To do that, they use an elaborate system of pumps to push your blood and the dialysate past each other separated by an artificial membrane, thereby filtering the blood of its wastes. Now, if you choose CAPD, you will use your own, built-in membrane inside your body. And you will be changing the solution yourself about every four to six hours during the day.

Changing containers and solutions can be very easy to do, and the details are covered in your training manual. Be sure to carefully read all of the instructional material your dialysis center will give you. From time to time, the tubing from the catheter to the container will have to be changed (every few months or so). You will not have to do this yourself, however. It will be changed by experienced personnel at your dialysis center.

The other task you need to perform is to check the catheter and the area around it periodically. Be aware of any redness or swelling of the skin near the catheter, and immediately report any changes in color, swelling or pain to your dialysis center or your doctor.

Observe the clarity of the used dialysate and report any cloudiness in the solution or any accompanying abdominal pain to your physician or your dialysis center immediately. Also be watchful for nausea, vomiting, diarrhea, abdominal distension, bloating or tenderness. Both the clarity of the drained solution, as well as the presence of abdominal pain and unusual gastrointestinal symptoms, could be the first signs of peritonitis. Peritonitis is an infection within your abdominal cavity and needs to be treated immediately.

In mild cases of peritonitis, antibiotic medication may be all that is necessary. By observing symptoms early and receiving proper treatment, recovery is usually uneventful. More severe cases may require hospitalization.

Being careful and observant will always pay off. On CAPD, you will be able to do more, move around more, and probably feel better than you have felt in a long time.

How much physical activity can I do?

Your level of activity should be a matter between you and your doctor. Generally, however, perform those physical activities you feel comfortable doing, and do nothing that might pull on or dislodge the catheter. Also, try to avoid activities that might contaminate the sterile connection between the container and the tube. This must be protected at all times.

What if I do a lot of traveling?

Travel should not be a problem. If you are only going to be gone for a short time, pack the number of solution containers and prep kits that you will need during the time you will be gone with a couple of extras in case of delays during travel. If you are going to be gone for an extended period of time, your dialysis center can give you the names of centers near your destination where supplies are available. Or, you can arrange with your dialysis supplier to have supplies sent to your destination.

What about solution exchanges at work?

Solution exchanges at work can be done with little or no difficulty... let your employer know you are under a doctor care. Then, just locate a private, clean space and do just what you would do at home.

All this has got to affect my family ...

... for the better! No more gearing your life around a machine ... so there is more time for them. All they will need is a little understanding. For instance, pets must be kept away from the area where you do the solution exchange. Children or grandchildren should not take a flying, although affectionate, leap into your lap. This might dislodge the catheter. Furthermore, your family should understand that you should not be interrupted during the solution exchange. Your concentration is very important, so that sterility is maintained. Pending any diet restrictions your doctor may specify, you can eat almost everything your family eats... no more special meals (which should make the "cook" very happy).

The relationship with your family should only improve after you begin CAPD. Even intimate relations with your spouse need not present problems. The tube and container are just an extension of yourself that is helping you to function normally and should not come between two people who love and support each other. Family support can make all the difference between success and failure in CAPD. Encouragement, understanding, taking the time to learn about CAPD, helping when you need help ... all these things are qualities that only members of a family can give to one another.

We hope that this booklet has been helpful in explaining CAPD and how you can benefit from the freedom CAPD can give you. CAPD uses a natural membrane to work with a special solution placed in your abdominal cavity to help filter the blood of its toxic wastes and remove excess fluid. The dialysis solution is placed into your abdominal cavity via a small tube, and this solution is changed by you every four to six hours during the day. With a little effort on your part, and a little understanding from your family, CAPD should be a new and exciting means of restoring a feeling of greater freedom and independence.

From a booklet (without permission) "Using the "kidney" you never thought you had"

Fresenius USA, Inc

2637 Shadelands Drive

Walnut Creek, CA 94598


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