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The Use of Peritoneal Dialysis in the Management of Kidney Failure
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By Jack W. Moncrief, MD, FACP Peritoneal dialysis (PD) is one of the generally available and internationally used forms of treatment and management of patients who reach end-stage kidney failure. It is the primary form of treatment for renal failure used at home and for self-dialysis. In order for a dialysis technique to be successful, it must include treatment of two fundamental processes that no longer spontaneously occur due to the absence of kidney function: removing waste products and removing water. Removing Waste Products Dialysis involves removal of the toxic waste products that result from metabolism, the process that provides energy for our bodies. The source of these products is the non-usable part of food and nutrition that is available for energy production, tissue repair, growth, and health. Just as an automobile requires gasoline, part of which is unusable and is emitted as exhaust or heat, the body has its own exhaust system. This takes the form of volatile waste—breath, solid waste (stool), heat, water—and water-soluble waste (urine). "Kidney poisoning" is the result when the kidneys can no longer remove the urine. Therefore, dialysis is required to rid the body of this water-soluble waste material. PD is performed by placing fluid (dialysate) into the patient's abdomen (the peritoneal cavity). The lining of this cavity, which lies on the surface of the intestine and the inside wall of the abdomen, is rich in blood supply The kidney poisons move from this blood supply into the fluid, thereby separating the poisons from the body. The contaminated fluid is then drained from the body and discarded and is replaced by fresh fluid, which stays (dwells) in the body until the next exchange of fluid. An adequate flow of this fluid, as well as good contact with the membrane that surrounds the peritoneal cavity, is necessary to complete the procedure and remove enough poisons to prevent uremia (a condition resulting from the advanced stages of kidney failure in which urea and other waste products accumulate in the blood)—in other words, “kidney poisoning.” Several techniques are available for placing (infusing) the fluid into the body, allowing the fluid to dwell in the body, and then draining the fluid. These techniques can be adjusted to the needs and desires of the individual patient and to his or her life schedule. Removing Water The second fundamental process required for the dialysis technique to be successful involves the adequate removal and maintenance of body water to prevent fluid overload, high blood pressure (BP), lung congestion, and heart stress (heart failure). This part of the procedure is called ultrafiltration. With PD, ultrafiltration is performed by placing a varying amount of sugar (glucose) in the PD fluid. This glucose pulls water from the bloodstream and causes it to accumulate in the abdominal cavity, where it is available for drainage and removal. Water, Water Everywhere Most of the food we eat is actually water. A beef steak or sandwich are over 60% water. Anything that will slosh in a glass (such as a soft drink) should be considered 100% water. A small amount of excess water escapes from the body by the process of breathing. Another small amount is emitted by sweat. The majority of fluid, however, is removed by the normal functioning of the kidneys. When renal function is lost and urine output stops, fluid removal becomes totally dependent upon dialysis. It is essential that the total intake of water ingested by patients who have kidney failure be balanced with the total removal of the excess water by dialysis. If this is not done, major complications will occur. For instance, if too much water is removed, low BP, shock, fainting, and even death can occur. If too little water is removed, hypertension (high BP), tissue swelling (edema), lung congestion, and heart failure can occur. A Delicate Balance Achieving this balance is fairly easy when one understands that each pint of water weighs one pound. It’s simple to achieve a stable body weight by closely monitoring the body weight adjusting the amount of fluid removed (done by adjusting the glucose added to the PD fluid). Close monitoring of the BP is also required, because PD is a slow process and the BP does not rapidly change. CAPD and APD Continuous ambulatory peritoneal dialysis (CAPD) and automated PD (APD) are the standard forms of the technique used to infuse and drain the dialysis fluid. With CAPD, the patient performs a single exchange upon rising from bed in the morning. The dialysate (fluid) is left in the abdomen while the person goes about his or her daily activities. A second exchange is usually performed at noon, followed by a third procedure in the early evening. A fourth and usually final exchange is carried out right before bedtime. These four daily exchanges, lasting about 30 minutes each, are usually enough for adequate management of both poison removal and ultrafiltration. With APD, a device delivers a measured amount of dialysis fluid into the abdomen (from a heated bag) at a specifically scheduled time during the night. A scheduled dwell time is set, and an automatic drain is accomplished during the night. This usually requires connection to the device for about 10 hours, 6 to 7 nights per week. Education, Adherence, and Long-Term Commitment Except in rare circumstances, these techniques are self-administered. Therefore, it is essential that the individual accept responsibility for carefully performing the technique as instructed by expert medical personnel. The techniques have been standardized for adequate poison and water removal in order to prevent the signs and symptoms associated with kidney failure. They are designed for long-term management and, with careful and disciplined application, should allow good health maintenance and personal vigor. PD allows many patients to enjoy an excellent lifestyle, including continued employment, family participation, and travel while using PD. Historical data on thousands of patients have allowed the medical community to recommend this technique to those individuals who are able and willing to accept the responsibility and independence of self-dialysis. PD allows patients to continue their independent life experiences without the encumbrance of having to travel to a dialysis facility three times a week. The timing of the exchanges can easily be adjusted to fit family and employment requirements, thereby reducing interference with lifestyle commitments. For instance, exchanges can be delayed or temporarily interrupted and "made up" when necessary to accommodate air travel, family emergencies, work requirements, and other activities. A good general understanding of the requirements for treating uremia to make the exchanges successful and to keep the patient's body in as healthy a state as possible is essential. Conclusion Many patients have a fear of taking on the responsibility of their own dialysis because it appears complex and dangerous. But peritoneal dialysis has allowed many thousands of patients to continue to be independent and remain close, productive members of their own families and social groups in spite of the fact that they have to meet the long-term requirements of treating kidney failure. Life expectancy and mortality rates associated with the use of PD have been favorably compared with the many scientific long-term studies pertaining to standard hemodialysis. The choice of doing PD or in-center hemodialysis is a lifestyle choice. But many experts in the field, as well as many patients, agree that PD offers a superior lifestyle. About the Author Jack W. Moncrief, MD, FACP, is the co-inventor with Robert Popovich, PhD, of CAPD. He is also the President and Co-Director of the Moncrief-Popovich Research Institute, Austin, TX. Moncrief is a recipient of the prestigious Torchbearer Award from the American Kidney Fund and the First Annual Belding H. Scribner Award from the American Society of Nephrology.
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