Medihub - Medical Information - Renal Medicine - Promises and Problems in Peritoneal Dialysis

Dialysis is treatment to replace kidney function. It does not cure the kidney disease; neither does it replace the function of the kidney entirely. The normal kidneys primarily remove waste products (which for simplicity will be called salt) and regulate water balance in the body; dialysis to some degree mimics these two important functions, which medication alone cannot do in the patient with end stage kidney disease.

Dialytic therapy however cannot replace the factory-like function of the kidney in producing substances (called hormones) that keep in balance the blood composition as well as the bone composition; additional medication must be given in a dialysis patient to replace these two functions. Nevertheless, with dialysis, patients with end stage kidney disease can live longer, feel better and in many instances return back as much as possible to their previous lifestyle.

The more traditional form of dialysis is called haemodialysis. Most patients know about this better in Singapore because of the widespread publicity of its availability.

Haemodialysis uses an artificial membrane that functions as an alternative kidney, and requires blood to be drawn from the body to pass alongside this membrane for cleansing (or rather dialysis). Each session of dialysis lasts on average 4 hours, and most patients will require about dialysis thrice weekly. For each session the patient must travel to a dialysis center, and during each session, the patient is hooked up to a machine and cannot move about.

A patient needs to have created on his wrist or arm an arteriovenous fistula in anticipation of haemodialysis. This is the lifeline of the haemodialysis patient. It is essentially a vein, which is artificially made stronger than usual to withstand the large blood flows required for efficient haemodialysis.

A poor fistula is usually associated with poor quality haemodialysis. With haemodialysis, many lives have been restored, which is what it is intended to do.

There is however another equally viable form of dialysis available that the public may know less well about. This is called peritoneal dialysis. Peritoneal dialysis (or PD) uses a natural pre-existing membrane in the body as a substitute for kidney function.

The membrane exists within the abdomen, and is called the peritoneal membrane. This membrane normally does not function like a kidney; however in certain circumstances it can. This membrane can mimic the function of waste removal and excess fluid removal from the body like the normal kidney when specialized fluid is placed into the abdomen.

This process is called peritoneal dialysis. Blood is not drawn from the patient for cleansing. Instead, fluid is placed into the abdominal cavity, where water and salt removal occur. The dialysate is replaced each time with a fresh dialysate for the process of dialysis to continue.

A typical form of PD is called Continuous Ambulatory peritoneal dialysis (CAPD), where 4 exchanges are done a day in the morning, noon, evening and prior to sleeping. Each exchange consists of an initial drain of fluid from the cavity, followed by a dwell of a fresh dialysate, which typically is between 2 to 2.5 litres. The process of exchange takes about 30minutes. After the fresh dialysate is instilled, the patient is free to go about his day as he needs to until the next exchange.

The process of exchange essentially is manually done; no machine is used for the exchange. Because of this, the treatment can be done almost anywhere.

Treatment can be done as much as at home, as well as in an office environment away from the home, making it suitable for the home bound patient as well as the working executive.

Like a haemodialysis patient, a PD patient also needs a surgical operation to prepare for PD therapy. A tube or catheter is electively inserted into the abdomen; this catheter tube allows the free flow of fluid into as well as out of the abdomen. As the arteriovenous fistula is the lifeline to the haemodialysis patient, so is the PD catheter the lifeline of the PD patient.

There are other variants of PD. Probably the most exciting form is Automated PD. PD exchanges are done in the sleeping hours of the patient and not in the day as in the typical CAPD pattern.

These night exchanges are done by a machine, hence the word automated. In a typical APD, the patient hooks himself up to the machine, which he leaves by his bedside. The machine performs the fluid exchanges, including removal and reinfusion several times at night while he sleeps. He disconnects himself from the machine in the morning, and the rest of the day is left free for him to do his work uninterrupted. The social advantages of this system are immediately apparent. It is the major form of night-time dialysis and frees the patient's day. It is also home based therapy.

PD from a patients perspectives can offer some unique advantages over HD. Each patient however is different and the choice of therapy is based on medical factors, and the patients choice, availability of home care, ease of travel and lifestyle.

Some advantages of PD are:

1. PD exchanges can be done in most relatively clean environments; it can be done at home or at the office.

Because of this it is suitable for those who prefer to be home, but it retains its versatility for it to be done even at environments away from home. PD offers home therapy for patients who prefer not to or perhaps cannot travel regularly to a HD center, these may include the elderly or those more infirmed with limited mobility. However, the mobile working adult may still do PD with a day exchange at midday in his office environment away from home.

Patients who require a free day, or families with little daytime help, can do APD. Patients with busy schedules do particularly benefit from having APD, which is essentially night-time dialysis leaving the `awake' hours free. For the families, APD releases the helpers burdens and only requires them to help the patient at home at the morning and evening hours.

2. PD provides slow, continues therapy. Fluid is always left in the abdomen; where there is fluid there is continuous removal of salt and water. The situation is more akin to that of a continuously functioning kidney, unlike a HD situation where water and salt removal occurs intermittently only 3x per week.

The continuity of salt and fluid removal does have an impact on the patient's diet.The daily fluid removal allows a more continuous fluid intake and dietary intake. The other advantage of PD is that is `slow' therapy. The word `slow' is better equated with `gentle' rather than `inefficient'.

Slow therapies provide less severe cardiovascular instabilities in patients with underlying heart disease, and can be advantageous in patients with severe heart failure or severe coronary artery disease.

3. There are other advantages that are briefly mentioned. PD does not require anti-blood clotting medication during the dialysis procedure unlike that of HD. This is advantageous to patients who have underlying diseases that can potentially bleed during a HD procedure, like active peptic ulcer disease, or severe diabetic eye disease or patients with aortic aneurysms.

4. Finally, from a medical perspective, PD preserves whatever little function of the kidney there is better that does HD. This little function is not enough alone to sustain life, but certainly it does help to reduce the dialysis requirements to compensate for the loss of function of the native kidneys.

PD therapy is not a panacea. It has its own inherent disadvantages and limitations as well. Its complications include the following:

- Catheter related infections can occur, just as the arteriovenous fistula can get infected in the haemodialysis patient. However, the rate of catheter infections have come down significantly with improved use of superior connection systems, as well as modern exit site care protocols. Catheter related infections cause abdominal pain and fever, but most cases respond well to antibiotic therapy. Patients who do not respond to antibiotic therapy need to have their
catheter removed. Under these circumstances, PD therapy is usually interrupted temporarily and haemodialysis instituted until the infection clears and the catheter can be reinserted safely.

- Some patients feel uncomfortable with the tube there permanently. About 4 to 6 cm of the tube exits from the abdomen site. When not in use it can be rolled up inconspicuously. Unfortunately, a patient with a PD catheter should not take up swimming, as pool water can potentially infect the catheter. Patients on PD therapy however can continue most land-based sports.

- Some patients feel uncomfortable with fluid in their abdomen. One might expect intuitively that smaller patients are more likely to have problems. However, our experience in this varies; we have had small 45 kg patients who have had no problems with 2 litres of fluid in the abdomen; conversely we have had 70kg patients who complain with the same volume of fluid instilled. Patients who do have complaints usually complain in the first one to two weeks of treatment, but subsequently these rarely persist.

In conclusion proper PD therapy is associated with good clinical outcomes comparable to that of HD. It is an equal viable alternative to most patients with end stage renal disease; in certain patient groups, it may even be preferrable. It allows a more liberated diet and fluid intake. APD is an available enhanced form of PD that has major social advantages with only night-time dialysis, and is an option of choice for the busy executive or the family structure with less daytime resource to help the home bound patient. It is another option for our patients suffering from end stage renal disease