What is dialysis?

What is dialysis?

The kidneys are responsible for filtering waste products from the blood. Dialysis is a procedure that is a substitute for many of the normal duties of the kidneys. The kidneys are two organs located on either side of the back of the abdominal cavity. Dialysis can allow individuals to live productive and useful lives, even though their kidneys no longer work adequately. In the United States, there are over 200,000 people who use dialysis techniques on an ongoing basis.
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, the 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."


In medicine, dialysis is primarily used to provide an artificial replacement for lost kidney function (renal replacement therapy) due to renal failure. Dialysis may be used for very sick patients who have suddenly but temporarily, lost their kidney function (acute renal failure) or for quite stable patients who have permanently lost their kidney function (stage 5 chronic kidney disease).
For patients with stage 5, or End-Stage Kidney Disease (ESKD), the decline in kidney function occurred over a period of months to years until a level was reached at which treatment was needed for survival. Unlike Acute Renal Failure (ARF) (Acute Kidney Injury (AKI)), Chronic Kidney Failure cannot be cured or reversed and long-term treatments are needed to replace the lost functions of the kidney. The treatment for ESKD that most naturally replaces lost kidney function is a kidney transplant. However, some patients are not good candidates for a transplant due to medical or other reasons, some cannot receive a transplant because of the short supply of donor kidneys, and others simply decide that a transplant is not the best option for them. As a result, most patients with ESKD must rely on dialysis to replace the water and waste removal functions of the healthy kidneys.
The kidneys have important roles in maintaining health. When healthy, the kidneys maintain the body's internal equilibrium of water and minerals (sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfate). Those acidic metabolism end products that the body cannot get rid of via respiration are also excreted through the kidneys. The kidneys also function as a part of the endocrine system producing erythropoietin and 1,25-dihydroxycholecalciferol (calcitriol). Erythropoietin is involved in the production of red blood cells and calcitriol plays a role in bone formation. Dialysis is an imperfect treatment to replace kidney function because it does not correct the endocrine functions of the kidney. Dialysis treatments replace some of these functions through diffusion (waste removal) and ultrafiltration (fluid removal).