What Is Dialysis?

Medically reviewed by Kashif J. Piracha, MD

Dialysis, also called "renal replacement therapy," is a medical procedure for people whose kidneys are working very poorly or not at all. Our kidneys are essentially the filters of our body, removing waste from our blood and turning it into urine. Although dialysis can’t perfectly do everything that normal kidneys can, some people can live for decades while on dialysis.

There are two types of dialysis: hemodialysis and peritoneal dialysis. Hemodialysis is separated into in-center hemodialysis, which occurs at a dialysis center, and home hemodialysis, which you can do at home. Peritoneal dialysis always occurs at home. Hemodialysis requires a machine known as an artificial kidney machine in order to filter your blood, whereas peritoneal dialysis uses an area in your abdomen to filter blood. Which type you use depends on your individual health requirements and restrictions.

How Dialysis Works

Your blood contains plasma, cells (white blood cells, red blood cells, and platelets), and other much smaller components. For example, it contains potassium, an electrolyte found in many foods, as well as waste products that can be toxic at high levels.

The kidney normally works hard to regulate particles like potassium, adjusting the amount released into the urine as needed, as not having the right amount can lead to health problems. Dialysis removes excess fluid from the body and some of these particles, as well as other waste products that would normally go out through your urine.

Hemodialysis

During hemodialysis, your blood is cleaned outside of your body. Some of the fluid and particles are removed, and the rest is returned to your body.

Blood from a vessel—usually from your forearm—travels through the dialysis device. Inside the device, it flows through a series of small tubes. The tubes are surrounded by a type of fluid, called dialysis fluid, which doesn’t have many particles inside it. These tubes are made of a semipermeable substance that lets some small particles and fluid flow through.

Because of the physics of osmosis and diffusion, some of the particles and fluid in the blood in these tubes flow into the surrounding dialysis fluid. This helps clean the blood while removing excess fluid.

The remaining components of the blood then flow back into a vessel in your arm. During a hemodialysis session, the blood flows through the device several times, leaving it much cleaner than it was before.

Peritoneal Dialysis

A different kind of dialysis, called peritoneal dialysis, uses some of the same principles, but it works a little differently. The blood isn’t cleaned outside the body, but inside the hollow space that surrounds the organs in your abdomen, called the abdominal cavity. The peritoneum is the lining of this hollow space and it contains many blood vessels.

Peritoneal dialysis uses a tube called a catheter that’s been surgically inserted near your belly button. Using the catheter, you put fresh dialysis fluid inside the abdominal cavity. Wastes and excess water are pulled from the blood vessels in the peritoneum into the dialysis fluid via diffusion and osmosis.

After a few hours, you drain the fluid that had been in the catheter tube and then refresh it with fresh dialysate fluid. This allows the blood to be cleaned more continuously than in hemodialysis. At night, you might use a device called a cycler that automatically drains and replaces the dialysis fluid for you. 

Who Needs Dialysis?

Dialysis is only for people who have very severe kidney disease, which is often called “kidney failure.” This can happen very suddenly or more gradually from a variety of medical conditions, including chronic diabetes, high blood pressure, genetic causes, or injury. In these people, the kidneys are working so poorly that they need either dialysis or a kidney transplant to survive.

Clinicians distinguish the severity of kidney disease based on stages. People who have the most severe degree of kidney failure, termed stage 5, are generally the ones who need dialysis. This is also sometimes called end-stage renal disease. These people have very low values of a kidney test called estimated glomerular filtration rate (eGFR), less than 15 mL/min.

Symptoms from kidney failure, like shortness of breath or confusion, are also key in deciding whether a person might need dialysis. Most people start to experience serious symptoms when their eGFR is between 5 and 10 mL/min.

Ultimately, the decision to start dialysis is a personal one. If you have chronic kidney disease, your healthcare provider will monitor you and have an ongoing discussion with you about your potential need for dialysis.

Related:Can You Reverse Kidney Disease?

Types of Dialysis

Although not all types of dialysis are an option for everyone, you may have choices about the best dialysis path for you.

In-Person Hemodialysis

Most commonly, people choose to have their dialysis performed at a dialysis center, one which might or might not be associated with a hospital. You’d usually have a fixed schedule for your treatments, typically three days a week. For example, you might be scheduled for treatments Monday, Wednesday, and Friday, with each treatment lasting four hours.

Some, but not all, dialysis centers also have options to get dialysis while you sleep. This frees up your days for other activities.

At-Home Hemodialysis

Another option is having hemodialysis in your home. You use a smaller version of the hemodialysis machines that are used at a center. You and a partner receive training to learn how to use the machine and how to insert the needles for dialysis.

Home hemodialysis gives you more flexibility with your treatment schedule. Most people do around four hours a day a few days per week.

However, you might work with your healthcare provider to figure out a schedule that works better for you. Some people do hemodialysis every other night or so for around eight hours. Another option is to do more frequent but shorter hemodialysis sessions (e.g., every day for two hours).

In general, hemodialysis scheduling that includes more frequent or longer dialysis sessions may help you feel better between sessions, and you might not need to be quite as strict with your fluid intake and your dietary choices.

Peritoneal Dialysis

With peritoneal dialysis, someone trains you to exchange the fluid inside your abdominal cavity yourself or with the help of someone at home. You insert the dialysate fluid through the catheter and then drain (and refill) several hours later.

In continuous ambulatory peritoneal dialysis (CAPD) you fill your abdominal cavity and drain it by hand several hours later. You need to do around four exchanges during the day and a longer one at night. But unlike hemodialysis, you are free to go about your normal activities between exchanges.

Another option is continuous cycling peritoneal dialysis (CCPD), also known as automated peritoneal dialysis (APD). In this method, you connect yourself to a machine called an automated cycler that does multiple exchanges of dialysis fluid while you sleep. You drain the fluid in the morning, but then don’t have to do more exchanges during the day unless you want to.

You can use both methods in any clean and private place, so it’s more convenient in that way than hemodialysis. Peritoneal dialysis might lead to fewer symptoms and reduced need for additional medications compared to hemodialysis. However, it isn’t an option for some people, either for medical reasons or because of other personal factors.

Peritoneal dialysis is usually painless, although it is sometimes a little uncomfortable. Some potential complications or side effects from peritoneal dialysis include:

• Infection of the peritoneum

• Infection of the catheter injection site

• Hernia (weakness of the abdominal muscle)

• Weight gain
  

Considerations for Treatment

Many people have questions about other aspects of dialysis treatment as well, including whether it will be covered by insurance or not, if any other procedures are needed, and what side effects may occur, among others.

Medical Coverage

Dialysis is expensive, and many people may be concerned about medical costs. However, dialysis is not unaffordable for most patients.

In the United States, people with kidney failure who need dialysis are eligible to enroll in Medicare, even if they don’t meet the standard age requirements. The government pays 80% of dialysis costs for most people. For people who have private health insurance as well, both Medicare and private insurance may pay part of the costs.

Surgical Procedures Before Dialysis

Hemodialysis can’t be performed through a vein, like how you might have had with an intravenous (IV) infusion. Instead, it needs to connect to the dialysis machine in a way that can withstand the strong flow and high volume of blood.

To create a safe dialysis access point, surgeons perform a minor surgical procedure before dialysis begins. Weeks or months before dialysis itself is to begin, the surgeons create the access point. Preferably, the surgeon connects an artery and a vein in your arm, termed an AV fistula. Some people need a slightly different procedure called an AV graft, which connects the arm vein and arm artery through a man-made tube.

If your kidney disease has progressed quickly, you might not have time for one of these options. In these cases, you might have a temporary catheter placed. This soft tube in your neck, chest, or groin area can give a temporary access point for dialysis, but catheters cause a lot more infections than AV fistulas or AV grafts.

People planning to have peritoneal dialysis also need to have a medical procedure done ahead of time. The doctor surgically implants the catheter tube inside the peritoneum.

Sometimes these procedures are done while you are awake but under local anesthesia to prevent you from feeling pain. In other cases, you might sleep under general anesthesia during the surgery.

Treatment Day

On the day of your hemodialysis treatment, it’s usually a good idea to eat a small meal or snack before your session. Many, but not all, onsite dialysis centers don’t allow patients to eat while having the hemodialysis session itself. It’s often a good idea to have something to eat after your session.

Many people are able to safely drive themselves to and from their dialysis appointments. However, you shouldn’t plan on doing this when you first start treatment, because you want to see how your body reacts. Some people might feel lightheaded after dialysis, or experience symptoms that make driving unsafe.

Because dialysis can affect the concentration of some medications, some people may need to take certain medications right after their dialysis session. Talk to your healthcare provider (typically a nephrologist, or a medical doctor who specializes in the kidneys) about when you should take your medications in the context of your dialysis schedule.

Side Effects

Occasionally, some people have side effects from dialysis, like headache or nausea. People undergoing hemodialysis are also at increased risk of certain health problems, such as:

• Anemia

• Electrolyte imbalances

• Infection

• Bleeding disorders

• Heart problems

You may experience some slight discomfort when the dialysis technician places the needle into your fistula or graft. Some people decide to get a little numbing agent before, so they won’t feel this. But dialysis itself is not painful.

Supporting Your Health

Dialysis can only restore some of your kidneys’ functions. To feel your best, you still need to take other steps, like taking your medications as prescribed. A health professional will also give you specific recommendations about the kinds of foods you should eat. For example, this might include:

• Limiting your intake of fluids

• Eating fewer foods that are high in salt, potassium, or phosphorus

• Eating more high-protein foods

Additionally, it’s critical not to skip dialysis sessions, whether you are getting them at a center or performing them in your home. 

A Quick Review

People who have very severe kidney disease need either dialysis or a kidney transplant. You can get hemodialysis, which cleans your blood while it’s outside the body, either at a medical center or in your home. Peritoneal dialysis is another option that you can perform yourself that cleans your blood while it’s inside your body. The type of dialysis you get depends on a variety of factors, so it's best to discuss your options with your nephrologist so they can help you determine what is best for you.

Frequently Asked Questions

Do you still pee on dialysis?

Some people still urinate while on dialysis, but some don’t. Overall, the longer you are on dialysis, the less likely it is that your body will still make urine.

Can you drink alcohol if you are on dialysis?

Most people on dialysis can have one or two drinks now and then without any problems. Heavier drinking causes greater health risks. If you are on dialysis, it is always best to discuss alcohol consumption with your nephrologist.

What foods should you avoid on dialysis?

Talk to your healthcare provider for more details, but people on dialysis should avoid, or at least limit, certain foods that are high in potassium.  Some of these are oranges, kiwis, nectarines, bananas, prunes, melons, and raisins and other dried fruit.

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