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What is hemodialysis and how does it work?
Hemodialysis is a treatment for kidney failure that uses a machine to filter your blood outside your body. At the start of a hemodialysis treatment, a dialysis nurse or technician places two needles into your arm. Once trained by the health care team, some people prefer to insert, or put in, their own needles. A pump on the hemodialysis machine draws your blood through one of the needles into a tube, a few ounces at a time. Your blood travels through the tube to the filter, called a dialyzer. Inside the dialyzer, your blood flows through thin fibers that filter out
- extra salt
- extra fluid
After the dialyzer filters your blood, a different tube carries your blood back to your body through the second needle.
Hemodialysis can replace part of your kidney function. Hemodialysis is not a cure for kidney failure; however, it can help you feel better and live longer.
You also may need to make changes to your diet, medicines, and liquid intake. Changes to your diet and liquid intake and the number of medicines you need will all depend on the amount of kidney function you have left and whether you receive treatments three times a week or more often.
Equipment and Supplies
Hemodialysis requires several pieces of equipment and many supplies for each treatment. The hemodialysis machine, dialyzer, dialysis solution, and needles are four of the most important parts in hemodialysis treatments:
Hemodialysis machine. The hemodialysis machine at a dialysis center is about the size of a microwave. Machines for home hemodialysis are small enough to sit on an end table. The hemodialysis machine has three main jobs:
- pump blood and regulate blood flow through the dialyzer
- monitor blood pressure
- control the rate of fluid removal from your body
Blood is removed from the body through one needle and propelled by a blood pump, which is, essentially like a rolling pin on the outside of the tube. The blood passes through the dialyzer and then is returned to the body through the other needle. Along the way, there are blood pressure monitors and detectors to ensure the procedure is safe. The blood, while it does pass outside of the body, remains inside the tubes or in the dialyzer and does not actually go into the hemodialysis machine.
Dialyzer. The dialyzer is the “artificial kidney.” Blood enters at the top of the dialyzer, in this case, and is forced into multiple, very thin, hollow fibers made of a semi-permeable membrane. Each fiber is about the size of a human hair. As blood passes through the hollow fibers, dialysis solution passes in the opposite direction on the outside of the fibers. In the less than one second it takes for the blood to pass from the top of the dialyzer to the bottom, waste products diffuse out of the blood and into the dialysis solution.
Dialysis Solution. Also known as dialysate, dialysis solution contains water and added substances that allow the safe removal of wastes and extra salt and fluid from your blood during dialysis. Your doctor will prescribe a specific dialysis solution for your treatments. If you have problems such as low blood pressure or muscle cramps during your treatments, your doctor can prescribe a solution with a different balance of chemicals. Your doctor might also adjust your solution if your blood tests show that your blood has too much or too little of certain minerals, such as potassium or calcium.
Needles. You, a nurse, or a technician will insert two needles into a vein, usually in the arm, at the start of each hemodialysis treatment. One needle draws blood that goes to the dialyzer, and the other needle returns the filtered blood to your body. When you first start hemodialysis treatments, the needle insertions may be one of the most uncomfortable parts of the treatment. Most people get used to them after a few treatments. If you find the needle insertions painful, you can put a numbing cream or spray on your skin so you won’t feel the needles.
Many people who have their treatments at a dialysis center have their needles inserted by a nurse or technician; however, you may prefer to insert your own needles. You’ll need training on inserting needles properly to prevent infection and keep your vein healthy. With a little practice, you can become good at inserting needles. Whether you insert your own needles or have it done by a nurse or technician, you should learn how to care for the area where the needles are inserted to prevent infection.
What is a vascular access?
A vascular access is an artificial connection between an artery and a vein where blood is diverted toward the vein. The resulting high blood flow through the vein causes the vein to expand and thicken. A vascular access lets high volumes of blood flow continuously during hemodialysis treatments to filter the greatest possible amounts of blood per treatment. A vascular access may be
- long lasting—more durable
- temporary—used for a short time
A long-lasting vascular access takes weeks to months to mature, or grow stronger, after the procedure to create the access. Ideally, a working access is in place before your first hemodialysis treatment. You should work closely with your nephrologist—a doctor who specializes in kidney problems—and vascular surgeon—a surgeon who works with blood vessels—to make sure the access is in place in plenty of time.
The veins in your arm are your “lifeline,” and it is important to protect them prior to starting dialysis. If an arm vein is damaged by an IV line or by repeated blood draws, it may not be suitable for the surgery described below. If you are approaching dialysis, remind health care providers to draw blood and insert IV lines only in veins below your wrist.
Long-lasting Vascular Access
An arteriovenous (AV) fistula and an AV graft are the two types of long-lasting vascular accesses.
AV fistula. A vascular surgeon creates an AV fistula by connecting an artery directly to a vein. An artery is a blood vessel that carries blood from the heart to the rest of the body. A vein is a blood vessel that carries blood from the body back to the heart. The vascular surgeon usually places an AV fistula in a person’s forearm or upper arm. An AV fistula causes the vein to expand and thicken, providing easy, reliable access to blood vessels. Doctors often recommend the AV fistula over the other types of access because it
- provides adequate blood flow for dialysis
- lasts a long time
- has a lower complication rate than other types of access
You may need to stay overnight in the hospital, or you may be able to go home after the procedure. You will get local anesthesia to numb the area where the vascular surgeon creates the AV fistula. Depending on your situation, you may get general anesthesia, in which you are not awake during your procedure.
AV graft. If your vascular surgeon cannot create an AV fistula because of problems with your veins, you may need an AV graft instead. An AV graft is a connection from an artery to a vein using a synthetic, or man-made, tube that is usually bent or looped. You may need to stay overnight in the hospital, or you may be able to go home after the procedure. You will get local anesthesia to numb the area where the vascular surgeon creates the AV fistula. Depending on your situation, you may get general anesthesia during your procedure.
You can use an AV graft soon after it is inserted. An AV graft is more likely to have problems with infection and blood clots. The repeated formation of blood clots can block the flow of blood through the AV graft and make it hard or impossible to do the hemodialysis treatment.
Temporary Vascular Access
If your kidney disease has progressed quickly, you may not have time to get a long-lasting vascular access before starting hemodialysis. In this case, you may require a venous catheter—a small, soft tube inserted into a vein in your neck, chest, or leg near the groin—as a temporary access. A nephrologist or an interventional radiologist—a doctor who uses medical imaging equipment to perform operations—performs the placement of the venous catheter in a hospital or an outpatient clinic. You will receive local anesthesia and sedation to keep you calm and relaxed during your procedure.
The catheter splits in two after the tube exits your body. The two tubes have caps designed to connect to the arterial line, which carries your blood to the dialyzer, and the venous line, which carries blood from the dialyzer back to your body. Clamps on the tubes can be closed if one of the lines is disconnected.
Although not encouraged, some people use a venous catheter for long-term access. When a person needs a venous catheter for more than 3 weeks, the vascular surgeon will “tunnel” the catheter under the skin, rather than insert it directly into the vein. A person will be more comfortable and have fewer complications with a tunneled catheter than with a nontunneled catheter.
More information is provided in the NIDDK health topic, Vascular Access for Hemodialysis.
Where can I do hemodialysis?
You can do hemodialysis at a dialysis center or at home. Each location has its pros and cons.
Hemodialysis at a Dialysis Center
Most people in the United States on hemodialysis have their treatments at a dialysis center. At the dialysis center, nurses and patient care technicians do most of the tasks, such as setting up the machine and inserting the needles. You will have a team of health care workers to help you with various needs. In addition to the nurses and patient care technicians, your health care team will include
- your doctor
- a dietitian
- a social worker
If you choose treatments in a dialysis center, you will have a fixed time slot, usually three times per week: Monday, Wednesday, and Friday or Tuesday, Thursday, and Saturday. If you work or have children to care for, you will need to consider that when choosing a dialysis schedule. Some dialysis centers offer nighttime treatments. This treatment occurs over a longer period while you sleep 3 nights a week at the center. Getting longer overnight dialysis treatments means
- fewer diet changes
- a more normal liquid allowance—how much liquid you can drink
- your days are free
Your doctor, nurse, or social worker can help you find a dialysis center that is convenient for you. You have the right to choose the dialysis center where you will receive treatment. Your doctor will give your medical information to the dialysis center you choose.
Most large cities have more than one dialysis center to choose from. You can visit the centers to see which one best fits your needs. For example, you can ask about their rules for laptop and cell phone use as well as for having visitors.
You may want the center to be close to your home to reduce your travel time. If you live in a rural area, the closest dialysis center may be far from your home and require a lot of travel time. If you would have a hard time getting to the dialysis center, you may want to consider home dialysis treatments, such as home hemodialysis or peritoneal dialysis.
More information is provided in the NIDDK health topic, Peritoneal Dialysis.
To help you choose a dialysis center, the Dialysis Facility Compare website, gives quality ratings for all U.S. dialysis centers. The website is maintained by Medicare, the Federal Government health insurance agency that pays most of the costs of hemodialysis and the other treatments for kidney failure. If you have supplemental insurance, your health plan may also have a list of centers you can use.
If you choose to do your hemodialysis treatments at home, you will still need to choose a dialysis center so you can learn how to perform the treatments and take care of the equipment. You will get your hemodialysis machine from the dialysis center. You will also go back to the center once a month for tests that will show how well your hemodialysis treatments are working.
Home hemodialysis lets you do longer or more frequent dialysis, which comes closer to replacing the work healthy kidneys do. Home hemodialysis lets you choose a schedule that fits the way you live. You can do daily home hemodialysis 5 to 7 days per week for 2 to 3 hours at a time, and you set the schedule. You can do nightly home hemodialysis three to six times per week while you sleep. Your doctor will determine how many treatments you need each week for daily home hemodialysis or for nightly home hemodialysis.
Daily home hemodialysis or nightly home hemodialysis will let you have a more normal diet and liquid allowance. You will also have fewer blood pressure medicines to take than you would with a standard schedule in a dialysis center.
For home hemodialysis, you must first learn how to perform treatments at the dialysis center, working with a dialysis nurse. You must learn how to
- insert your own needles
- monitor your vital signs
- set up and clean the hemodialysis machine
If these procedures are not done correctly, you could have serious problems.
Most dialysis centers require that you have a trained partner in your home during hemodialysis treatments, so you must ask a family member or friend to go through training with you. In addition to providing training and a hemodialysis machine that stays in your home, the dialysis center also provides 24-hour support if you have a question or problem. Some programs also monitor treatments over the Internet. Training often takes 3 to 8 weeks.
More information is provided in the NIDDK health topic, Home Hemodialysis.
Dialysis Center and Home Hemodialysis Comparison Chart
Use the following chart to help you choose between hemodialysis in a dialysis center and home hemodialysis.
||Three treatments a week for 3 to 5 hours or more. Monday, Wednesday, Friday or Tuesday, Thursday, Saturday.
||Flexible. Three to seven short or long treatments per week at times that work best for you.|
||Available in most communities; may require travel in some rural areas
||Becoming more widely available as smaller equipment is developed|
||The clinic has the machine and supplies.
||The machine and 2 to 4 weeks’ worth of supplies are in the home. You may need minor changes to hook the machine to electricity and water in your home.|
||The clinic teaches about treatments, diet, liquids, medicines, lab tests, etc.
||You and a partner must attend 3 to 8 weeks of home hemodialysis training.|
|Diet and Liquids
||Strict limits on liquids, phosphorus, sodium, and potassium
||Fewer limits on liquids or diet, based on the amount of hemodialysis and lab tests|
|Level of Freedom
||Less freedom on treatment days. May feel washed out and tired for hours after each treatment.
||You set the treatment schedule, fitting in all prescribed treatments. Work and travel are much easier.|
|Amount of Work
||Center staff do hemodialysis tasks. They can teach you to do some tasks.
||You and your partner must set up, run, and clean the machine; check vital signs; track the treatments and send in forms; and order supplies.|
||Medicare and most other health plans cover three hemodialysis treatments a week.
||Medicare covers three hemodialysis treatments a week and may cover more for medical reasons; other health plans may cover all hemodialysis treatments.|
What problems could I have with hemodialysis?
You could have problems with your vascular access, which is the most common reason for hospitalization for people on hemodialysis. Any type of vascular access may
- become infected
- have poor blood flow or blockage from a blood clot
These problems can keep your treatments from working. You may need to have more procedures to replace or repair your access for it to work properly.
Rapid changes in your body’s water and chemical balance during treatment can cause other problems as well. Muscle cramps and sudden hypotension—a drop in blood pressure—are two common side effects. Hypotension can make you feel weak, dizzy, or sick to your stomach. Your doctor can make changes to your dialysis solution prescription, which can treat these problems.
You may need a few months to adjust to hemodialysis. You should always report problems to your doctor and dialysis staff so they can treat your side effects quickly and easily. You can prevent many side effects if you follow a proper diet, limit your salt and liquid intake, and follow your doctor’s instructions for taking your medicines.
More information about problems that can occur with kidney failure is provided in the NIDDK health topic, Kidney Failure: What to Expect.
What changes will I have to make when I start hemodialysis?
One of the biggest changes you will have to make when you start hemodialysis treatments is following a strict schedule. Also, adjusting to the effects of kidney failure and the time you spend on dialysis can be hard. You may feel tired after treatments. You may need to make changes in your work or home life, giving up some activities and responsibilities. Keeping the same schedule you had when your kidneys worked can be hard now that your kidneys have failed. Accepting these changes can be hard on you and your family. A mental health counselor or social worker can answer your questions and help you cope.
How will I know my hemodialysis treatments are working?
You will know your hemodialysis treatments are working by how you feel. Most people with kidney failure feel better after starting dialysis treatments. Your appetite usually improves and your energy levels increase. Hemodialysis reduces salt and fluid buildup, so you should have less shortness of breath and swelling as well.
The key to making the most of your hemodialysis treatment is to keep to your ideal “dry weight.” Your ideal dry weight is your weight when you do not have extra fluid in your body. If you are careful about the salt in your diet and the hemodialysis is working, over time, you should be able to reach your ideal dry weight at the end of every hemodialysis treatment. When hemodialysis treatments are working and you keep to your ideal dry weight, your blood pressure should be well-controlled.
In addition, blood tests can show how well your hemodialysis treatments are working. Once a month, whether you are on home or dialysis center hemodialysis, your dialysis nurse will test your blood using one of two types of lab tests:
- Kt/V is a score given as a number. Experts recommend a minimum Kt/V of 1.2. A single score below 1.2 should not worry you; however, your average Kt/V should exceed 1.2.
- urea reduction ratio (URR) is a score given as a percentage. Experts recommend a minimum URR of 65 percent. A single score below 65 percent should not be of great concern; however, your average URR should exceed 65 percent.
Both tests look at changes in one specific waste product, called blood urea nitrogen (BUN), to gauge the overall level of waste products in your system. Your BUN is measured before and after a dialysis treatment to see how much of it has been removed.
More information about these tests is provided in the NIDDK health topic, Hemodialysis Dose and Adequacy.
What financial help is available to pay for hemodialysis?
U.S. citizens who have kidney failure are eligible to receive Medicare. Treatment for kidney failure costs a lot; however, Medicare pays much of the cost, usually up to 80 percent. Often, supplemental insurance pays the rest. For people who are not eligible for Medicare or who still need help with the portion that Medicare does not cover, states have Medicaid programs that provide funds for health care based on financial need. Your social worker can work with you to locate resources for financial help.
More information is provided in the NIDDK health topic, Paying for Kidney Failure Treatment.
Eating, Diet, and Nutrition
Eating the right foods can help you feel better when you are on hemodialysis. Talk with your dialysis center’s dietitian to find a hemodialysis meal plan that works for you. Your dietary needs will depend on your treatment and other factors, such as your weight and activity level. Staying healthy with kidney disease requires watching how much of the following are included in your diet:
Protein is in many foods you eat. Protein is in foods from animals and plants. In general, most diets include both animal and plant proteins. Protein provides the building blocks that maintain and repair muscles, organs, and other parts of your body. Most people on hemodialysis are encouraged to eat high-quality protein because it maintains a healthy body. High-quality protein comes from meat, fish, and eggs. However, many high-protein foods also contain phosphorus, which can weaken your bones. Talk with your dietitian about ways to get the protein you need without getting too much phosphorus.
Read more in the National Kidney Disease Education Program (NKDEP) fact sheet Protein: Tips for People with Chronic Kidney Disease.
Phosphorus is a mineral that keeps your bones healthy and your blood vessels and muscles working. Phosphorus is found naturally in foods rich in protein, and it is also added to many processed foods. However, phosphorus can weaken your bones and make your skin itch if you have too much. Hemodialysis may not remove enough phosphorus, so you will probably need to limit or avoid high-phosphorus foods especially those with phosphorus added to improve flavor or keep them from going bad, such as lunch meats. You may also need to limit milk and cheese, dried beans, peas, colas, nuts, and peanut butter. In addition, you may need to take a pill with meals called a phosphate binder that keeps phosphorus in your food from entering your bloodstream.
Read more in the NKDEP fact sheet Phosphorus: Tips for People with Chronic Kidney Disease.
Fluid includes water and drinks such as fruit juice and milk; and water in foods such as fruits, vegetables, ice cream, gelatin, soup, and ice pops. You need water for your body to function properly; however, too much can cause swelling and make your heart work harder. Over time, too much fluid in your body can cause high blood pressure and congestive heart failure. Fluid builds up in your body between hemodialysis treatments, resulting in swelling in your ankles and hands. Limiting the amount of liquid you have can help you prevent these problems. You can tell that you have too much fluid in your body if your body weight goes too far above your dry weight.
Sodium is a part of salt. Sodium is found in many canned, packaged, frozen, and fast foods. Sodium is also found in many condiments, seasonings, and meats. Too much sodium makes you thirsty, which makes you drink more liquid. Try to eat fresh foods that are naturally lower in sodium, and look for products labeled “low sodium,” especially in canned and frozen foods. Pay attention to the amount of sodium in milligrams (mg) listed on the nutrition facts label of food products.
Read more in the NKDEP fact sheet Sodium: Tips for People with Chronic Kidney Disease.
- Potassium is a mineral that helps your nerves and muscles work the right way. People with kidney failure who do not make enough urine can have a buildup of potassium in their blood. Hemodialysis balances the potassium level in your blood by removing extra potassium from your blood. Potassium levels that are too high or too low can cause heart problems and, if severe enough, can lead to sudden death due to an abnormal heartbeat. You can prevent your potassium level from going too high between hemodialysis treatments by avoiding high-potassium foods, including bananas, oranges, potatoes, and tomatoes.
Read more in the NKDEP fact sheet Potassium: Tips for People with Chronic Kidney Disease.
Calories are units of energy. Calories in food give you the energy you need. Many people on hemodialysis do not have a good appetite and do not get enough calories. If you find it hard to eat, talk with your dialysis center’s dietitian to find healthy ways to add calories to your diet.
Supplements help provide some of the vitamins and minerals that may be missing from your diet because you have to avoid many foods. Hemodialysis also removes some vitamins from your body. Your doctor may prescribe a vitamin and mineral supplement designed specifically for people with kidney failure. Never take vitamin and mineral supplements that you can buy over the counter. They may be harmful to you. Talk with your doctor before taking any medicines, including vitamin and mineral supplements that are not prescribed for you.
You may have a hard time with changing your diet at first. However, eating the right foods will help you feel better. You will have more strength and energy. More information is provided in the NIDDK health topic, Eat Right to Feel Right on Hemodialysis.
Points to Remember
- Hemodialysis is a treatment for kidney failure that uses a machine to filter your blood outside your body.
- Hemodialysis is not a cure for kidney failure; however, it can help you feel better and live longer.
- Hemodialysis can replace part of your kidney function. You also may need to make changes to your diet, medicines, and liquid intake.
- A vascular access is an artificial connection between an artery and a vein where some of the blood is diverted toward the vein. The resulting high blood flow through the vein causes the vein to expand and thicken. A vascular access lets high volumes of blood flow continuously during hemodialysis treatments to filter the greatest possible amounts of blood per treatment.
- A long-lasting vascular access takes weeks to months to mature, or grow stronger, after the procedure to create the access. Ideally, a working durable access is in place before your first hemodialysis treatment. You should work closely with your nephrologist—a doctor who specializes in kidney problems—and vascular surgeon—a surgeon who works with blood vessels—to make sure the access is in place in plenty of time.
- Doctors often recommend the arteriovenous (AV) fistula over the other types of access.
- If you are approaching dialysis, remind heath care providers to draw blood and insert IV lines only in veins below your wrist.
- If you choose treatments in a dialysis center, you will have a fixed time slot, usually three times per week: Monday, Wednesday, and Friday or Tuesday, Thursday, and Saturday.
- If you would have a hard time getting to the dialysis center, you may want to consider home dialysis treatments such as home hemodialysis or peritoneal dialysis.
- Home hemodialysis lets you do longer or more frequent dialysis, which comes closer to replacing the work healthy kidneys do.
- Blood tests can show how well your hemodialysis treatments are working.
- Treatment for kidney failure costs a lot; however, Medicare pays much of the cost, usually up to 80 percent. Often, supplemental insurance pays the rest. Your social worker can work with you to locate resources for financial help.
- Eating the right foods can help you feel better when you are on hemodialysis.
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About the Kidney Failure Series
You and your doctor will work together to choose a treatment that's best for you. The publications of the NIDDK Kidney Failure Series can help you learn about the specific issues you will face.
Learning as much as you can about your treatment will help make you an important member of your health care team.
This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.
The NIDDK would like to thank:
Scott D. Bieber, D.O., University of Washington, and Jonathan Himmelfarb, M.D., University of Washington.
This information is not copyrighted. The NIDDK encourages people to share this content freely.