Kidney Dialysis Health Article

Definition

Dialysis treatment replaces the function of the kidneys, which normally serve as the body's natural filtration system. Through the use of a blood filter and a chemical solution known as dialysate, the treatment removes waste products and excess fluids from the bloodstream, while maintaining the proper chemical balance of the blood. There are two types of dialysis treatment: hemodialysis and peritoneal dialysis.

Purpose

Dialysis is most commonly prescribed for patients with temporary or permanent kidney failure. People with end-stage renal disease (ESRD) have kidneys that are no longer capable of adequately removing fluids and wastes from their body or of maintaining the proper level of certain kidney-regulated chemicals in the bloodstream. For these individuals, dialysis is the only treatment option available outside of kidney transplantation. Dialysis may also be used to simulate kidney function in patients awaiting a transplant until a donor kidney becomes available. Also, dialysis may be used in the treatment of patients suffering from poisoning or overdose in order to quickly remove drugs from the bloodstream.

Demographics

As of December 31, 2000, in the United States, over 275,000 people were undergoing regular dialysis treatments to manage their ESRD. Diabetes mellitus is the leading single cause of ESRD. According to the 2002 Annual Data Report of the United States Renal Data System (USRDS), 42% of non-Hispanic dialysis patients in the United States have ESRD caused by diabetes. People of Native American and Hispanic descent are at an elevated high risk for both kidney disease and diabetes. ESRD caused by diabetes occurred in 65% of Hispanic dialysis patients. And of those Native Americans who had been on dialysis for one year in 1999, 82% had diabetes.

Hypertension (high blood pressure) is the second leading cause of ESRD in adults, accounting for 25.5% of the patient population, followed by glomerulonephritis (8.4%). African-Americans are more likely to develop hypertension-related ESRD than whites and Hispanics.

Among children and young adults under 20 on dialysis, glomerulonephritis is the leading cause of ESRD (31%), and hereditary, cystic, and congenital diseases account for 37%. Pediatric patients typically spend less time on dialysis than adults; according to the USRDS the average waiting period for a kidney transplant for patients under age 20 is 10 months, compared to the adult wait of approximately two years.

Description

There are two types of dialysis treatment: hemodialysis and peritoneal dialysis.

Hemodialysis

Hemodialysis is the most frequently prescribed type of dialysis treatment in the United States. The treatment involves circulating the patient's blood outside of the body through an extracorporeal circuit (ECC), or dialysis circuit. Two needles are inserted into the patient's vein, or access site, and are attached to the ECC, which consists of plastic blood tubing, a filter known as a dialyzer (artificial kidney), and a dialysis machine that monitors and maintains blood flow and administers dialysate. Dialysate is a chemical bath that is used to draw waste products out of the blood.

Since the 1980s, the majority of hemodialysis treatments in the United States have been performed with hollow fiber dialyzers. A hollow fiber dialyzer is composed of thousands of tube-like hollow fiber strands encased in a clear plastic cylinder several inches in diameter. There are two compartments within the dialyzer (the blood compartment and the dialysate compartment).

The membrane that separates these two compartments is semipermeable. This means that it allows the passage of certain sized molecules across it, but prevents the passage of other, larger molecules. As blood is pushed through the blood compartment in one direction, suction or vacuum pressure pulls the dialysate through the dialysate compartment in a countercurrent, or opposite direction. These opposing pressures work to drain excess fluids out of the bloodstream and into the dialysate, a process called ultrafiltration.

A second process called diffusion moves waste products in the blood across the membrane and into the dialysate compartment, where they are carried out of the body. At the same time, electrolytes and other chemicals in the dialysate solution cross the membrane into the blood compartment. The purified, chemically balanced blood is then returned to the body.

Most hemodialysis patients require treatment three times a week, for an average of three to four hours per dialysis "run." Specific treatment schedules depend on the type of dialyzer used and the patient's current physical condition.

Blood pressure changes associated with hemodialysis may pose a risk for patients with heart problems. Peritoneal dialysis may be the preferred treatment option in these cases.