By Marlo Sollitto
Healthy kidneys clean blood by removing excess fluid, minerals, and wastes. They also make hormones that keep bones strong and blood healthy. When the kidneys fail, harmful wastes build up in the body, blood pressure may rise, and the body may retain excess fluid and not make enough red blood cells. When this happens, treatment is needed to replace the work of your failed kidneys.
There are two types of dialysis: hemodialysis and peritoneal dialysis. Hemodialysis is the more prevalent treatment in the U.S.
In hemodialysis, a device called a dialyzer (or artificial kidney) is used to remove excess fluid and waste products from the bloodstream. During the treatment, blood travels out of the patient, through blood tubing, a dialysis machine, and a dialyzer (known collectively as the dialysis circuit), and back into the patient again.
To provide easy access to a person's vascular system, a surgically implanted access site called a fistula or graft is created, usually on the arm. This is where blood exits and re-enters the dialysis patient's body through attached catheters. Sometimes a catheter is inserted into a vein for temporary vascular access while a person awaits a permanent access site.
When the person's blood passes through the dialyzer, an artificial membrane within it acts as a filter. Dialysate, a liquid solution, is cycled through one side of the membrane while blood is pumped through the other. Toxins and excess fluids are filtered from the bloodstream and into the dialysate fluid, and electrolytes pass from the dialysate across the dialyzer membrane and into the bloodstream. The clean and chemically balanced blood is shuttled back into the body via the vascular access.
Hemodialysis treatment is typically administered three times a week, and takes three to four hours (depending on the person's clinical needs and the type of dialyzer used). It is usually performed in a dialysis unit — a dedicated dialysis clinic that is located in a freestanding outpatient center or within a hospital setting. Home hemodialysis is also a treatment option, but because it requires a significant investment in both training and equipment, the majority of U.S. ESRD patients undergo dialysis in a center.
Peritoneal dialysis (PD) uses the lining of the abdomen (peritoneum) to filter toxins from the bloodstream. A surgically implanted catheter is used to fill the abdominal cavity with dialysate. The peritoneum is similar to a hemodialysis membrane, drawing toxins out of the blood and into the dialysate-filled abdominal cavity. The waste-filled dialysate is then removed from the abdominal cavity after a prescribed period of dwell time. This is known as an exchange. The various types of PD are explained below.
- Continuous Ambulatory Peritoneal Dialysis (CAPD). The patient inserts a catheter into the abdomen and infuses a fresh supply of dialysate. The process is performed several times during the day (usually a four to six hour exchange each time) and once while sleeping through the night.
- Continuous Cyclic Peritoneal Dialysis (CCPD). A machine, or cycler, performs the dialysate exchange in CCPD. It will perform several cycles during the night, and then one or two daytime exchanges that last the entire day.
- Intermittent Peritoneal Dialysis (IPD). IPD, sometimes called NIPD (nocturnal intermittent peritoneal dialysis) also uses a cycler to perform six or more exchanges at night. However, unlike CCPD, there is no daytime exchange.
Grafting a healthy kidney from a cadaver or living donor is a complex process. The donor kidney and the transplant candidate must be tissue matched for antigen compatibility. The kidney has six antigens (which stimulate the production of antibodies), and compatibility is based on how many of the antigens match up from donor to candidate — the more the better. After transplant, a life-long regimen of immunosuppressive medication is required, leaving the patient at increased risk for infections due to the weakened immune system.
Although the majority of transplants come from cadaver organ donors, living kidney donations are becoming much more commonplace. Living donor kidneys have a significantly higher survival rate than cadaver kidneys (at five years, living donor kidney transplants have a 78.4% graft survival rate compared to 64.7% for cadaver kidney transplants).
Transplanted kidneys do not last forever; the average life of a cadaver graft is less than 15 years and rejection of the kidney can occur at any time. However, the life span of transplanted kidneys has increased dramatically over the past decade, and there are transplant recipients who have had functioning grafts for over 35 years.
According to the National Kidney and Urologic Diseases Information Clearinghouse, the graft survival rate in 2001 following a cadaver transplant is:
- 1 year: 87.7%
- 2 years: 82.8%
- 5 years: 64.9%
- 10 years: 37.1%
For a living-donor transplant, the survival rate is:
- 1 year: 94.1%
- 2 years: 91.1%
- 5 years: 77.7%
- 10 years: 56.5%