Dialysis is a procedure that eliminates waste and excess fluid from the blood. This treatment may be necessary when the kidneys stop functioning properly. Dialysis typically involves diverting blood into a machine that filters it and returns it to the body.

Healthy kidneys remove waste products, maintain electrolyte levels, and regulate blood pressure. However, when the kidneys are no longer able to perform these tasks, a person may require dialysis to keep their body in balance.

This article will discuss dialysis in more detail, including the different types, how to prepare, and the potential risks.

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People may require dialysis, or renal replacement therapy, when they experience kidney failure, which can be either acute or chronic. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) classifies kidney failure as a decrease in kidney function to below 15% of the normal function. A person who loses 85–90% of their kidney function will likely be a candidate for dialysis.

Dialysis is a procedure that mimics the natural work of the kidneys.

What do the kidneys do?

The kidneys are vital organs that play an important role in the urinary system. They filter the blood, removing waste and excreting it as urine.

Learn more about what the kidneys do.

The kidneys should be able to filter about 150 quarts of blood each day. If disease, injury, or other factors prevent these organs from functioning as they should, salts and other waste products can accumulate in the blood and damage organs, making a person seriously ill.

Dialysis carries out the work of the kidneys, using a machine to filter and purify the blood before returning it to the body. It keeps fluids and electrolytes in balance, allowing the body to function as normal.

Although dialysis can mimic the role of the kidneys, it is not a cure for chronic kidney disease or other problems affecting the kidneys. People will require other treatments to address the underlying condition.

There are three types of kidney dialysis:


Hemodialysis is a procedure that uses a dialysis machine and a special filter called a dialyzer. Some people may refer to a dialyzer as an artificial kidney.

During the treatment, a healthcare professional will insert two needles into a blood vessel, typically in the arm, to connect the person to the machine. The machine then pumps the person’s blood through the dialyzer filter and returns it to their body. It also measures blood pressure, controls how quickly blood flows through the filter, and determines how much fluid to remove from the body.

Inside the machine, the blood passes through hollow fibers, and a dialysis solution passes in the opposite direction outside the fibers. Waste products move from the blood to the dialysis solution, and the filtered blood then returns to the body. A dialysis session typically lasts about 4 hours.

A person can get hemodialysis either in a hospital, in a dialysis center, or at home.

Peritoneal dialysis

Peritoneal dialysis is a form of dialysis that uses the lining of the belly, or the peritoneum, to filter blood.

There are two types of peritoneal dialysis: continuous ambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis (APD).


This method does not require a machine. Instead, it uses a bag full of dialysis solution, which contains water, salt, and other additives. A person connects the bag full of dialysis solution to their stomach via a catheter. The solution then flows into the stomach and absorbs waste and extra fluid from the body.

After a few hours, a person drains the solution and waste into an empty bag. They can then start over with a fresh bag of dialysis solution. It may be necessary to perform a dialysis exchange between three and five times every day.


This method is similar to CAPD, but it uses a machine called a cycler to deliver and drain the dialysis solution. Some people may also refer to this type of peritoneal dialysis as continuous cycler-assisted peritoneal dialysis (CCPD).

A person can perform CAPD or APD in any clean private place, such as at home or work.

Continuous renal replacement therapies

Continuous renal replacement therapy (CRRT) is a special type of dialysis to treat acute renal failure. A doctor may suggest CRRT for people in the intensive care unit when hemodialysis is unsuitable. It may be a good option for individuals who are hemodynamically unstable, which means that they have abnormal or fluctuating blood pressure that results in improper circulation.

CRRT is similar to hemodialysis, but instead of requiring multiple 4-hour sessions, the treatment lasts 24 hours, as it slowly and continuously filters blood.

There are three main types of CRRT:

  • Continuous venovenous hemofiltration (CVVH): CVVH uses convection to filter blood.
  • Continuous venovenous hemodialysis (CVVHD): CVVHD uses diffusion to filter blood.
  • Continuous venovenous hemodiafiltration (CVVHDF): CVVHDF combines both methods.

The preparation for dialysis will differ slightly depending on the method. Typically, it will involve a surgeon implanting a device to gain access to a person’s bloodstream, which is usually a quick operation.

It is advisable for a person to wear comfortable clothing during dialysis treatment and to follow any guidance from their doctor. For example, this could include a period of fasting before the treatment.


A person will require vascular access surgery to receive hemodialysis. This minor surgery allows a person to connect to the dialyzer easily. A vascular surgeon may fit either an arteriovenous (AV) fistula, an AV graft, or a catheter so that a person can readily get dialysis.

A doctor or renal dietitian may also advise some people to eat a special diet to prevent waste buildup in between dialysis treatments. The diet plan might involve increasing protein intake while limiting electrolytes and fluids. The person’s body size, nutritional status, and kidney condition will determine the exact amount of protein that they need.

Peritoneal dialysis

As with hemodialysis, a person will need minor surgery to place a catheter on their stomach. After a surgeon fits the catheter, a person will get training to learn how to perform exchanges by hand and avoid infections. A person who chooses APD will receive additional training in how to use the cycler.

Although anyone who receives dialysis may need to follow a diet plan, hemodialysis typically requires a more strict one than peritoneal dialysis. The reason for this is that peritoneal dialysis takes place more frequently, so waste products are less likely to accumulate.


A person does not need to prepare for CRRT. A doctor will quickly determine whether a person requires the treatment and will make the necessary preparations.

The risks of dialysis will vary slightly depending on the type of dialysis.


Common problems with hemodialysis include infection, poor blood flow, and blockage of the vascular access. In some cases, people may experience changes in their water and chemical balance, which can cause muscle cramps or a sudden drop in blood pressure. A loose needle could also result in blood loss, which could lead to severe complications.

Peritoneal dialysis

It is important that people regularly wash their hands to avoid an infection around the catheter and prevent peritonitis. Peritonitis is an infection of the fluid in the stomach, and it can cause pain, fever, nausea, and vomiting. Anyone who experiences these symptoms should speak with a doctor.

Learn more about peritonitis here.

Peritoneal dialysis can also increase the risk of a hernia because the catheter requires an opening in the body. In addition, it can sometimes cause weight gain due to the body absorbing the sugar in the dialysis solution.


Similar to the other methods, the risks of CRRT include infection, hypotension, and electrolyte disturbances.

Dialysis is a treatment that helps filter the blood when the kidneys are not functioning correctly. If a person experiences either acute or chronic kidney failure, they may require dialysis to substitute the role of the kidneys.

Different types of dialysis include hemodialysis, peritoneal dialysis, and continuous renal replacement therapy. Although each method differs slightly, dialysis typically uses a machine and special fluid to remove harmful waste and extra salt and water from the blood.