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Dialysis is a treatment that filters and purifies the blood using a machine. This helps keep your body in balance when the kidneys can't do their job. Dialysis has been used since the 1940s to treat people with kidney problems.

Dialysis helps the body by performing the functions of failed kidneys. The kidney has many roles. An essential job of the kidney is to regulate the body's fluid balance. It does this by adjusting the amount of urine that is excreted on a daily basis. On hot days, the body sweats more. Thus, less water needs to be excreted through the kidneys. On cold days, the body sweats less. Thus, urine output needs to be greater in order to maintain the proper balance within the body. It is the kidney's job to regulate fluid balance by adjusting urine output. Another major duty of the kidney is to remove the waste products that the body produces throughout the day. As the body functions, cells use energy. The operation of the cells produces waste products that must be removed from the body.


When these waste products are not removed adequately, they build up in the body. An elevation of waste products, as measured in the blood, is called "azotemia." When waste products accumulate they cause a sick feeling throughout the body called "uremia," which is due to urea and other nitrogenous waste compounds.

A healthy person's kidneys filter around 120 to 150 quarts of blood each day. If the kidneys are not working correctly, waste builds up in the blood. Eventually, this can lead to coma and death. The cause might be a chronic, or long-term condition, or an acute problem, such as an injury or a short-term illness that affects the kidneys. Dialysis prevents the waste products in the blood from reaching hazardous levels. It can also remove toxins or drugs from the blood in an emergency setting.

There are different types of dialysis.The three main approaches are:

  • Intermittent hemodialysis (IHD)
  • Peritoneal dialysis (PD)
  • Continuous renal replacement therapies (CRRT)

The choice will depend on factors such as the patient's situation, availability, and cost.

Intermittent hemodialysis

In hemodialysis, the blood circulates outside the body of the patient. It goes through a machine with special filters.The blood comes out of the patient through a flexible tube known as a catheter. The tube is inserted into the vein.Like the kidneys, the filters remove the waste products from the blood. The filtered blood then returns to the patient through another catheter. The system works like an artificial kidney.Patients who are going to have hemodialysis need surgery to enlarge a blood vessel, usually in the arm. Enlarging the vein makes it possible to insert the catheters.

Peritoneal dialysis

While hemodialysis removes impurities by filtering the blood, peritoneal dialysis works through diffusion. In peritoneal dialysis, a sterile dialysate solution, rich in minerals and glucose, is run through a tube into the peritoneal cavity, the abdominal body cavity that surrounds the intestine. It has a semi-permeable membrane, the peritoneal membrane. Peritoneal dialysis uses the natural filtering ability of the peritoneum, the internal lining of the abdomen, to filter waste products from the blood.

The dialysate is left in the peritoneal cavity for some time, so that it can absorb waste products. Then it is drained out through a tube and discarded. This exchange, or cycle, is normally repeated several times during the day, and it can be done overnight with an automated system. The elimination of unwanted water, or ultrafiltration, occurs through osmosis. The dialysis solution has a high concentration of glucose, and this causes osmotic pressure. The pressure causes the fluid to move from the blood into the dialysate. As a result, more fluid is drained than is introduced.

Peritoneal dialysis is less efficient than hemodialysis. It takes longer periods, and it removes around the same amount of total waste product, salt, and water as hemodialysis.

Continuous renal replacement therapies (CRRT)

Dialysis can be intermittent or continuous. While a session of intermittent dialysis lasts for up to 6 hours, continuous renal replacement therapies (CRRT) are designed for 24-hour use in an intensive care unit (ICU). There are different types of CRRT. It can involve either filtration or diffusion. It is better tolerated than intermittent dialysis, because the solute or fluid removal is slower. This leads to fewer complications.

In some cases, the kidneys recover and do not need further treatment.