How Does Dialysis Work

The kidneys are an important part of human anatomy that filters excess water and wastes from the blood and excretes them in the urine. The kidneys also secrete chemicals into the bloodstream that are used to help regulate blood pressure and help initiate red blood cell creation and bone formation. If the kidneys have reached a point of failure that is above 80%, then the individual who is suffering from kidney failure may need to go on dialysis in order to continue to get rid of the extra water and wastes.

How Does Dialysis Work


A dialysis machine has been designed to mimic the filtration process that occurs in a healthy kidney. If you have ever had the privilege of learning how diffusion works, then you know that particles in water will pass from areas of high concentration to areas of low concentration if they are small enough to fit through the holes in a membrane. The kidneys take advantage of the principle of diffusion when they filter the blood. Within the kidneys, there are small chambers (Bowman’s Capsules) that contain a collection of very small blood vessels. As the blood passes through the vessels in these chambers, molecules move from the bloodstream into the network of tubes that form urine.

When someone asks, how does dialysis work, it is usually easiest to explain it in terms of the process that occurs in the kidney. The dialysis machine contains a semipermeable membrane that allows water and waste materials to leave the blood and enter a special dialysis fluid that is on the opposite side of the membrane. The filtered blood is then returned to the patient’s bloodstream and the waste material is disposed of. Although the dialysis machine is not as efficient as a healthy kidney in discerning the products that should be filtered and those that need to be returned to the bloodstream, it does allow for patients who would otherwise die from kidney failure to live for an extended period of time. Many of the inefficiencies of a dialysis machine can be compensated for through supplementation.

How Does Dialysis Work in Hemodialysis Patients

There are two common forms of dialysis that work in different ways. The form of dialysis that most people think about when they hear the term is hemodialysis. This type of dialysis involves an external machine that the blood passes through in order to be filtered. As the blood flows by the semipermeable member, waste cross the membrane and enter the special dialysis fluid on the other side. Bicarbonate is allowed to diffuse in the opposite direction of wastes so that it can help neutralize the metabolic acidosis that commonly results from the procedure. Traditionally, patients have had this procedure performed in a dialysis center three to fives times per week, but technology has now advanced to the point where many patients are able to perform dialysis at home on a more frequent basis. This has proven to be beneficial for the health of dialysis patients.

How Does Dialysis Work in Peritoneal Patients

Peritoneal dialysis patients undergo a procedure in which the filtration process occurs inside the abdomen. In this type of dialysis, the peritoneal membrane within the abdomen is used as a natural semipermeable membrane. The peritoneal membrane is effective as a membrane because it contains the blood vessels that line the abdominal cavity and internal organs. The wastes that are collected in the special dialysis fluid are drained from the abdomen through a tube. This type of dialysis is usually performed five to seven times per day and can be administered overnight. While peritoneal dialysis is less efficient than hemodialysis, it does allow patients to avoid having to make trips to the dialysis clinic each week.

There are two primary types of peritoneal dialysis that patients use. Continuous Ambulatory Peritoneal Dialysis (CAPD) is usually performed by the patient and it does not require the use of machines. The dialysate is placed inside the peritoneal cavity through a catheter and is drained into a bag approximately four or five hours later. The bag can then be discarded. The other type of peritoneal dialysis is called Automated Peritoneal Dialysis (APD). APD utilizes a machine known as a cycler that shortens the diffusion exchange by about three to four hours. This type of dialysis is most commonly performed at home while the patient sleeps.

How Does Dialysis Work in Hemofiltration


Hemofiltration is a type of hemodialysis that does not use a special dialysis fluid in order to filter water and metabolic wastes. Instead, a pressure gradient is used to force water across the membrane causing it to take many waste molecules with it. A special fluid is used during the process to replace water and salts that are lost as a result of the filtration procedure. Other types of dialysis include hemodiafiltration and intestinal dialysis. These are not as common as hemodialysis and peritoneal dialysis.

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