When the kidneys fail due to injury or disease, it leads to dangerous accumulation of substances in the blood. Dialysis is a procedure that performs some of the functions of normal, healthy kidneys, including removal of fluid, electrolytes, and byproducts of cell metabolism. Dialysis can also help control blood pressure and maintain acid-base balance in the blood. When dialysis is required for a prolonged period of time, it is called chronic dialysis.
Chronic kidney failure leading to end-stage renal disease (ESRD) is the primary indication for chronic dialysis. In the United States, ESRD is most often the result of long-standing diabetes or high blood pressure. Without dialysis, ESRD is fatal. Several hundred thousand patients in the U.S. and several million worldwide receive chronic dialysis each year.
When to initiate dialysis for ESRD varies significantly from patient to patient. Generally, patients have lost 85 to 90 percent of normal kidney function and have symptoms of ESRD. In many, dialysis becomes necessary when other medical interventions are unable to adequately control fluid overload or high potassium levels in the blood.
Dialysis has been done as a routine treatment for ESRD since the 1960s. The patient’s blood is slowly passed through a semi-permeable membrane to filter out and remove fluid, electrolytes, and waste products, and then returned to the patient. The undesirable electrolytes and waste products are in a higher concentration in the blood than in the dialysis fluid and move from higher to lower concentration by simple diffusion. The dialysis fluid is called dialysate and is prescribed for each individual patient by a physician.
There are two main types of chronic dialysis: hemodialysis and peritoneal dialysis. Hemodialysis may be done in the hospital, in a dialysis clinic, or at home. The usual hemodialysis treatment schedule in the U.S. is three- to five-hour sessions, three times per week. In some patients, more frequent hemodialysis, up to five or six times per week, may better control the complications of ESRD.
During hemodialysis, the patient’s blood is run through a membrane called the dialyzer, and then returned to the patient. Less than one cup of blood is actually outside of the patient’s body in the dialysis machine at any given time. For chronic dialysis by this method, health care providers must be able to easily access the patient’s blood. This is usually done with an arteriovenous (AV) fistula, where a surgeon joins an artery and a vein under the skin in the forearm to make a larger blood vessel.
Continuous ambulatory peritoneal dialysis (CAPD) is the other option for patients needing chronic dialysis. The patient instills dialysate into his or her abdominal cavity through an implanted catheter, allows the fluid to remain for several hours, and then drains the dialysate out. The peritoneal membrane, which contains many small blood vessels, acts as the dialysis filter. CAPD dialysate contains lots of glucose, which creates a concentration gradient to pull excess water out of the blood.
CAPD must be done four to five times per day. It has the advantage of being able to be done at home, at work, or while traveling. Nevertheless, it requires a very motivated patient to keep up with all the daily exchanges. A related procedure, called continuous cycling peritoneal dialysis, can also be done at home. This type of dialysis does require a machine, which performs frequent exchanges for 10 to 12 hours at night.
During the dialysis procedure, patients may experience low blood pressure, muscle cramps, and itching. Over time, there is a risk of infection in the AV fistula, which may require hospitalization. Patients who are on dialysis for several years or more are at risk of developing amyloidosis. This is a condition caused by protein deposits in the joints and tendons.
Patients receiving any type of chronic dialysis have several requirements. They must be willing to follow the strict treatment schedule to prevent accumulation of fluid and undesirable electrolytes. In addition, they must limit or monitor fluid intake and follow a special diet that limits protein, sodium, potassium, and phosphate. Most patients on dialysis also take multiple medications, such as phosphate binders, erythropoietin, and calcium/vitamin D.
Unless ESRD patients are able to receive a kidney transplant, chronic dialysis must be done for life. It may seem to be a cumbersome procedure, given the strict schedules and restrictions. In spite of this, chronic dialysis can allow patients with ESRD to live for many years.