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Definition of Renal Dialysis
Dialysis can be short term or long term. Though in theory renal dialysis could sustain life indefinitely, in practice most people experience a steady decline of overall health with long-term dialysis because artificial methods of cleansing toxins from the blood are not as effective, efficient, or thorough as the natural processes the kidneys perform.
However, it is not uncommon for people to use renal dialysis for 10 to 20 years or longer. There are two general types of renal dialysis: hemodialysis and peritoneal dialysis.
Hemodialysis filters toxins directly from the blood. The person goes to a hemodialysis center for each dialysis treatment. A catheter inserted into a blood vessel, usually in the arm, routes the blood circulation externally through a machine that removes toxins. The cleansed blood then returns to the body through a second catheter. When hemodialysis is long term, the doctor places a permanent arteriovenous (AV) shunt that connects an artery and a vein. The dialysis machine’s cannulas then connect to the shunt.
The hemodialysis machine consists of a pump and a container, called the dialyzer with a semiporous membrane inside. The membrane looks somewhat like the filter inside a water purification canister. On one side of the membrane is a solution called the dialysate. The dialyzer pumps blood into the container on the other side of the membrane. The dialysate attracts certain substances-minerals, electrolytes, and waste byproducts—to cross the membrane from the blood.
The dialysate absorbs these substances. Fresh dialysate circulates through the dialyzer at the same rate as the blood. The blood and the dialysate never come into direct contact with one another. Another type of filter traps any air bubbles that are in the blood before the blood returns to the body. The dialyzer holds only a few ounces of blood at a time. It takes three to five hours for the blood to circulate through the dialyzer enough times to remove an appropriate amount of waste and toxins. Most people need three hemodialysis sessions every week.
In the United States hemodialysis is the standard renal dialysis method. Many nephrologists feel it more thoroughly cleanses the blood. However, hemodialysis entails significant risks. Key among these risks are infection with hepatitis and other bloodborne conditions, injury to the blood vessels used to shuttle blood between the person and the dialysis machine, and microscopic damage to the blood cells.
Peritoneal dialysis makes use of a natural membrane in the body, the peritoneum, which encloses the abdominal cavity. It is a continuous process. Two catheters surgically inserted into the abdominal cavity serve as the portals through which dialysate enters and leaves the cavity. The doctor prescribes the dialysate, which comes premixed in single-dose bags.
The molecules of the dialysate are to large to pass through the peritoneum so the solution remains contained in the abdominal cavity. The blood’s natural circulation carries blood through the blood vessels (capillary networks) within the peritoneum. As with hemodialysis, the dialysate attracts certain molecules to cross the membrane into the dialysate. A second catheter carries dialysate out of the abdominal cavity. There are two stages to peritoneal dialysis, the exchange (draining the dialysate into and out of the abdominal cavity) and the dwell (the time during which the dialysate remains in the abdominal cavity.
Two types of peritoneal dialysis
- Continuous ambulatory peritoneal dialysis (CAPD) instills dialysate into the abdominal cavity using gravity to pull the dialysate into the catheter. The dialysate remains in the abdominal cavity for about four hours, then the person drains it out through the second catheter. Most people who use this method need four treatments each day. Aside from the 30 minutes it takes to instill the dialysate and the 30 minutes it takes to drain the dialysate, the person is unencumbered and goes about his or her regular activities.
- Continuous cycler-assisted peritoneal dialysis (CCPD) uses a pump to rapidly infuse and extract the dialysate at night when the person is sleeping, with dwell times of about two hours. The person then infuses the abdominal cavity with dialysate upon awakening, and retains the solution all day for a single long dwell time.
The primary advantage of peritoneal dialysis is mobility. Most people are able to participate in regular activities, including work, while peritoneal dialysis is under way, provided the person can perform exchanges on the necessary time schedule and there is a hygienic, private location where the person can do the exchange. The success of peritoneal dialysis is more variable than that of hemodialysis because the permeability of the peritoneum varies among individuals. Some doctors believe peritoneal dialysis is less effective than hemodialysis at clearing toxins from the body.
Benefits and Risks of Renal Dialysis
Renal dialysis is the difference between life and death for people who have end-stage renal disease (ESRD). For most people, the benefits clearly outweigh the potential risks and complications. The primary risks related to renal dialysis are infection, and, with hemodialysis, bleeding.
Renal dialysis becomes less effective over time because it simply is not as effective as the body’s natural mechanisms. A slow cascade of complications arises. Dialysis only cleanses the blood; it cannot restore kidney function or prevent further degeneration of the kidneys.
See also QUALITY OF LIFE.