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WHAT IS RENAL REPLACEMENT THERAPY? ? Renal replacement therapies are treatments for severe kidney failure, also called renal failure. When the kidneys are no longer working effectively, waste products and fluid build up in the blood. These therapies take over the function of the failing kidneys and remove the fluid and waste. ( See "Patient information: Overview of renal replacement therapy" ).

Renal replacement therapy is usually not needed until more than 90 percent of kidney function is lost. This usually takes many months or years after kidney disease is first discovered. Early in the course of kidney disease, other treatments are used to help preserve kidney function and delay the need for replacement therapy.

HOW DOES MY DOCTOR KNOW WHEN RENAL REPLACEMENT THERAPY IS NEEDED? ? As kidney disease progresses, the decision to begin dialysis is made by the patient and doctor after considering a number of factors. The patient's kidney function (as measured by blood and urine tests), overall health, quality of life, personal preferences, and other factors impact the decision. Doctors recommend that dialysis begin well before kidney disease has advanced to the point where life threatening complications might occur. There are also data to suggest that it is beneficial to begin dialysis before signs of malnutrition, a complication of kidney disease, are evident.

Certain clinical signs indicate that dialysis must be started immediately. If blood tests measuring kidney function fall outside certain parameters, or if the patient has symptoms such as mental confusion or bleeding that is related to kidney disease, dialysis should be started at once.

CHOICE OF RENAL REPLACEMENT THERAPY ? Once it is determined that renal replacement therapy will eventually be required, the patient should be counseled considering the advantages and disadvantages of the three types of therapy: hemodialysis (in-center or at home), peritoneal dialysis, and renal transplantation (living or cadaveric donor).

Kidney transplantation is the treatment of choice for end-stage renal disease. A successful kidney transplant improves the quality of life and reduces the mortality risk for most patients, when compared with maintenance dialysis. However, not all patients are appropriate candidates for this therapy because of absolute and/or relative contraindications to this procedure.

For these individuals and for those who are suitable transplant recipients but must wait for an available kidney, the choice between hemodialysis or peritoneal dialysis is influenced by a number of considerations such as availability, convenience, coexisting disorders, home situation, age, gender, and other considerations. This choice is best performed in consultation with the patient's family and physicians.

PREPARATIONS FOR HEMODIALYSIS ? If hemodialysis will be used for renal replacement, it is important to think about this well in advance to make necessary preparations. In particular, venous access should be established so that a functioning access is available at the time that dialysis must begin. As an example, an arteriovenous (AV) fistula, which connects an artery to a vein (see below) is the preferred form of vascular access; it should be placed two to four months before it is needed. Discussions about venous access should ultimately begin even earlier, since care must be taken not to traumatize blood vessels with frequent blood drawing in the arm that will eventually be used for access (most often the non-dominant arm).

In some patients, hemodialysis must be initiated prior to the placement and/or maturation of a permanent access. In this setting, a temporary venous catheter is placed for the dialysis sessions.

HOW IS HEMODIALYSIS DONE? ? In hemodialysis, the patient's blood is routed through a dialysis machine in order to remove waste products and fluids.

Removing waste products and fluid ? A dialysis machine works by putting the patient's blood in contact with a special solution, called dialysate, across a membrane. The membrane allows movement of fluid and substances between the blood and the dialysate. Certain substances in high concentration in the blood, such as the waste products the kidney normally removes, are in lower concentration or not present in the dialysate. This causes these substances to move from the blood, across the membrane, and into the dialysate in an attempt to equalize the concentration of the various substances.

Additional physical forces are also at work as blood is pumped through the machine, These forces cause more fluid and waste to move from the blood into the dialysate.

Vascular access ? The patient's blood is connected to the dialysis machine using a surgically constructed path called a "vascular access," usually referred to as an "access." The access creates a way for blood to be removed from the body, circulate through the dialysis machine, and then be returned to the body.

There are three major types of access: primary AV fistula, synthetic AV access, or central venous catheter.

Primary AV fistula ? This is the preferred type of vascular access. A surgeon creates a path between an artery and a vein, usually in the lower arm. The path, or fistula, sits under the skin. During dialysis, small needles are inserted into the fistula. Blood flows out through one needle, circulates through the dialysis machine, and flows back through the other.

A fistula cannot be used right away. It needs several months to "mature" before it can be used for dialysis.

Synthetic AV access, or bridge graft ? Sometimes, the patient's blood vessels are not suitable for creating a fistula. In these cases, the surgeon uses a small plastic tube, called a graft, to create the path between an artery and vein. The graft sits under the skin and is used in much the same way as the fistula to perform the dialysis.

Grafts mature more quickly than fistulas and can be used in about two weeks after they are created. However, complications such as narrowing or infection are more common in grafts than in AV fistulas.

Central venous catheter ? A tube (eg, venous catheter) can be placed into a large vein in the neck if dialysis must be done right away and the patient does not have a functioning AV fistula or graft. This type of access is usually used only on a temporary basis. In some cases, however, there are problems maintaining an AV fistula or graft, and the central venous route is used for long-term access.

WHERE IS HEMODIALYSIS DONE? ? Hemodialysis can be done either at a dialysis center or at home. Some dialysis centers are "free standing" (that is, they only do dialysis treatment); others are connected to hospitals. Home treatment is an option for some people, but requires special training and the right environment and home supports.

HOW WILL I FEEL DURING TREATMENT? ? The vast majority of hemodialysis sessions are extremely well tolerated. However, side effects can occur. These include:

Low blood pressure is the most common complication and can be accompanied by lightheadedness, shortness of breath, cramps, nausea, or vomiting. Treatments and preventive measures are available for the discomforts that may occur during dialysis.

HOW LONG DOES HEMODIALYSIS TAKE? ? Treatment times vary depending upon a number of factors related to each patient's condition. In general, hemodialysis takes between two and four hours and is done about three times a week.

WHERE TO GET MORE INFORMATION ? Your doctor is the best resource for finding out important information related to your particular case. Because every patient is different, it is important that your situation is evaluated by someone who knows you as a whole person.