Kidneys keep us healthy in many ways. One important kidney function is to help our bodies maintain a constant balance of chemicals and water, no matter what we eat or drink. For example, when we ingest extra salt or water, the kidneys excrete the excess in the urine to maintain proper levels within our bodies. As kidneys weaken or fail, our body chemistry changes. The changes can be dangerous. When the danger becomes too great, kidney function must be replaced by artificial means, called renal replacement therapy (“RRT”), to sustain life. Renal replacement therapy is kidney transplantation or dialysis. Dialysis is the procedure for artificially replacing many functions performed by normal kidneys. It is necessary to replace kidney function when kidneys are no longer able to keep people healthy and safe. There are two common types of dialysis: hemodialysis and peritoneal dialysis. Both types of dialysis remove toxins, metabolic breakdown products, fluid and excessive chemical build-up normally controlled by functioning kidneys. Both use the principles of chemical diffusion to accomplish these goals. Chemical diffusion is simply the passage of a substance in solution across a semipermiable membrane from a site of high concentration to one of lower concentration. This motion doesn’t need any energy outlay, like water running downhill or a child going down a slide on the playground.

The two types of dialysis use different semipermiable membranes to carry out chemical diffusion. Peritoneal dialysis uses the bodies own covering of the bowel and abdominal cavity as the semipermiable membrane. This membrane is called the peritoneal membrane, hence the name “peritoneal dialysis.” Special dialysis fluid, called dialysate, is instilled into the abdominal cavity through a thin plastic tube, called a peritoneal catheter. The catheter is inserted surgically below the belly button into the abdominal cavity. The catheter is below the beltline and is covered by the blouse or shirt, invisible to others. The dialysis fluid stays (“dwells”) in the abdomen for varying amounts of time, after which the fluid is drained and replaced with new, fresh fluid. As the dialysis fluid “dwells” in the abdominal cavity, fluid, chemicals and waste products leave the blood, across the peritoneal membrane into the dialysis fluid. Then the old fluid is drained out of the abdomen through the catheter and replaced with fresh dialysis fluid. The dialysis fluid is “changed” four to six times each day. There are two methods for changing the fluid. One method changes the fluid automatically with a machine. The machine is called a “cycler” because it automatically “cycles” the fluid. A cycle consists of: (1) inflow – placing new, fresh dialysis fluid into the abdominal cavity; (2) dwell – leaving the dialysis fluid in the abdominal cavity for approximately 4 to 6 hours; and (3) drain – removing the dialysis fluid. Cycles are repeated four to six times. After the last cycle, fresh dialysis fluid flows into the abdominal cavity, the catheter is disconnected from the cycler machine, capped, and you are then free to go about your usual daily business. Dialysis fluid dwells in the abdomen all day. At bedtime, the catheter is connected to the cycler machine, and the process repeats. Because dialysis fluid is in the abdomen 24 hours per day, seven days per week, the technique is called “continuous, cycler peritoneal dialysis” or “CCPD.” The second type of peritoneal dialysis involves manually (i.e. without a machine) changing the fluid during the day by connecting a hanging bag of dialysis fluid to the catheter. This allows the fluid to flow into the abdominal cavity by gravity. Then the catheter is disconnected from the empty bag. The catheter is sealed with a screw on cap. You tuck in your shirt or blouse, and go about your daily activities, letting the fluid dwell in your abdominal cavity for four to six hours. Then you sit in a quiet place and repeat the process of “exchanging” old dialysis fluid and dissolved wastes with new, fresh dialysis fluid. Between dialysis fluid exchanges, you are free to do almost anything you want while the fluid dwells in the abdomen. Therefore, this type of peritoneal dialysis is called “ambulatory” meaning “walking around.” Because there is fluid in the abdomen all the time, 24 hours a day, seven days a week, the technique is called “continuous.” You will hear this method called “CAPD” which stands for “continuous, ambulatory, peritoneal dialysis.” CCPD works at night, with a long dwell of fluid during the day. CAPD works during the day with a long dwell of fluid overnight. Hemodialysis uses an artificial membrane, outside the body, to perform chemical diffusion. The hemodialysis machine directly cleans the blood, therefore its name “hemo” dialysis. For the hemodialysis machine to work, there must be access to your blood. Blood is removed from your body via needles placed in a specially created blood vessel underneath the skin of an arm, usually the arm opposite the hand you use. This special blood vessel is called a fistula, or arterio-venous fistula (“AVF”). Two needles are inserted into the fistula, one to remove blood and the other to return blood. For every drop of blood removed from your body, a drop is returned, in a continuous fashion. Many people, just like you, learn to insert the needles themselves. It may sound difficult or uncomfortable, but after you learn how to do it, most people think it is easy. You can learn more about inserting your own needles. The process is called “self-care” and it can be done at home (“home hemodialysis”) or in a dialysis center. If you want to learn “self-care” later, nurses will place the needles for you.

Everyone receives an appointment time and day to come to the dialysis center. Then you sit in a large recliner chair and the needles are inserted. The hemodialysis machine is started and blood flows from your fistula through plastic tubing into and out of the artificial kidney, through more plastic tubing, through the second needle, and back into you. The blood flows continuously from you, through the artificial kidney and back into you. Hemodialysis usually takes four hours each treatment. Three treatments per week are needed, Monday-Wednesday-Friday or Tuesday-Thursday-Saturday. Each dialysis type has strengths and weaknesses, advantages and disadvantages. It is important to understand the advantages and disadvantages for each type of dialysis so you can select the one you think fits best with your lifestyle. Always ask your health professional about the “risks” and “benefits” of each treatment. You can also find more information on AAKP’s web site, www.aakp.org and in AAKP’s pamphlets.

When should renal replacement therapy (RRT) with dialysis begin? There is no simple or uniform answer. In general, when quality of life and safety are significantly compromised by kidney dysfunction, it is time for RRT. If too much water accumulates in the body, severe shortness of breath caused by congestive heart failure can occur. If too much potassium collects in the body, muscles, including the heart muscle, are weakened and eventually paralyzed. If too much acid accumulates in the body, bones thin, blood can’t carry oxygen normally, and cells don’t function normally. If too much metabolic waste builds up in the body, confusion, seizures, loss of appetite, nausea, vomiting, restless legs, twitching and other symptoms can occur. These symptoms are called the “uremic syndrome.” It is time to replace damaged kidney function when these complications occur. That said, it is even better to start replacing damaged kidney function before these complications occur. In general, the better you feel when you start renal replacement, the better you will continue to feel. This is the reason there is no simple or uniform answer to the question “when to start.”

Instead of waiting for symptoms and complications to occur, many use the numerical severity of kidney dysfunction to begin renal replacement. The degree of kidney function or dysfunction can be determined by calculating kidney function from a blood test, called serum creatinine. Creatinine is a pigment made by muscle tissue in a fixed amount and released into the blood every day. The only way creatinine can leave the blood is by kidneys filtering it and excreting it in the urine. Thus, serum creatinine is the inverse, or reverse, of kidney function. As kidney function decreases, serum creatinine increases. The higher the serum creatinine, the poorer the kidneys are working. Serum creatinine is entered into a mathematical formula (called the MDRD Equation) and the resulting number (called GFR, or glomerular filtration rate) shows the percent of normal the kidneys are working. For example, a GFR of 100 means the kidneys are working 100 percent, while a GFR of ten means the kidneys are only working ten percent of normal (90 percent of function has been lost). Starting dialysis is usually recommended when kidney function is 15 percent of normal or less (85 percent or more has been lost). If you know your serum creatinine level and have access to the Internet, you can calculate your own GFR (http://www.nkdep.nih.gov/professionals/gfr_calculators/orig_con.htm).

Because peritoneal dialysis catheters and AV fistulas must heal before they can be used for dialysis, planning for dialysis usually begins when kidney function is 30 percent or less. Planning includes learning about the risks and benefits, advantages and disadvantages, of transplant and dialysis. It can be helpful to have someone with you when you learn about treatment choices. Four ears and two brains are better than two ears and one brain! Afterwards, the two of you can compare notes and discuss what you learned. If new questions arise, you can ask them on the telephone, by e-mail (if available) or at your next visit. Questions are best asked when they are fresh in your mind.

When you understand your choices well enough, you can make an “informed” choice between treatment types. Once you choose, you can have the peritoneal dialysis catheter or hemodialysis fistula made months before it may be needed. If a peritoneal dialysis catheter or an AV fistula is not made at least six to 12 weeks before starting dialysis, the chances of needing emergency dialysis in the hospital or intensive care unit increase. If advanced planning does occur, the chances of a scheduled, non-emergent beginning of dialysis, with plenty of warning, is more likely. Scheduled initiation of dialysis means you can have maximum input into what to start and when to start.

It could be years before you need dialysis. You have the right and responsibility to know the treatment options available to you.  Ask questions of your healthcare team and make sure you understand the answers. Early detection and treatment can delay some of the problems brought on by CKD.

Answer provided by Dr. Richard Goldman. Dr. Goldman is a member of the AAKP Board of Directors, AAKP Medical Advisory Board and a retired renal physician.