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The kidneys have a very important function in the body. Healthy kidneys balance fluid and chemicals in the body, and remove harmful waste products. The kidneys also make hormones that help to control blood pressure, make red blood cells, and keep bones strong and healthy.

Dialysis can be used to remove waste products and excess fluid from the blood when the kidneys are unable to do this properly, such as in acute kidney injury or chronic kidney disease.

There are 2 main types of dialysis, haemodialysis and peritoneal dialysis. Peritoneal dialysis involves pumping dialysis fluid into the space inside the tummy (abdomen) to draw out waste products from the blood passing through blood vessels lining the inside of the abdomen.

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What is haemodialysis?

Haemodialysis is the most common type of dialysis. During haemodialysis, a tube is attached to a needle in your arm. Blood passes along the tube and into an external machine that filters it, before it's passed back into the arm along another tube.

Dialysis is usually carried out 3 days a week, with each session lasting about 3 to 4 hours. It is also possible for haemodialysis to be done at home instead of at a hospital renal dialysis unit.

Some people opt for daily haemodialysis (usually six days/week), which provides the best control of fluid balance and biochemistry but is very intensive.

When is haemodialysis needed?

Haemodialysis is needed when the kidneys are unable to remove waste products and excess fluid from the blood because of kidney failure, either because of a sudden condition affecting the kidneys (acute kidney injury), or when long term kidney disease (chronic kidney disease) has progressed to a point when the kidneys can no longer do this.

Dialysis can also be used to remove an excessive amount of a drug that has got into the blood stream, such as following an overdose.

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How does haemodialysis work?

Before a person starts dialysis, an arteriovenous fistula (AV fistula) must be created in the forearm (this connects an artery directly to a vein) to allow needles to be inserted and removed after each treatment, so that blood can flow from and back into the body during haemodialysis.

The joining of a vein and artery just under the skin makes the vein swell, but only a small scar and swelling are visible between treatments.

The operation to create the AV fistula is usually carried out about 4 to 8 weeks before haemodialysis begins. This allows the tissue and skin surrounding the fistula to heal. If the blood vessels are too narrow to create an AV fistula, an alternative procedure known as an AV graft may be recommended. A piece of synthetic tubing is used to connect the artery to the vein.

For each haemodialysis, 2 thin needles will be inserted into the AV fistula or graft and taped into place. One needle will slowly remove blood and transfer it to a machine called a dialysis machine. In the dialysis machine, blood flows along one side of a series of membranes, with a special fluid called dialysate flowing along the other side of the membranes.

The membranes have tiny holes of different sizes so that the excess fluid and substances which are at high levels in the blood pass through to the dialysate to clean the blood. The filtered blood is then passed back into your body through the second needle.

A dialysis machine regulates how fast the blood flows, at what pressure and how quickly the exchange happens. As only a very small amount of blood is in the dialysis machine at any given time, blood needs to circulate between the patient and the dialyser for about 4 hours.

Where is haemodialysis done?

Some people have to go to a hospital renal dialysis unit for haemodialysis. Other can have the necessary equipment installed at home. This will depend on what facilities your hospital can offer, on your medical conditions, and on your own preference.

Many renal units have developed satellite or minimum care units which may be near your home. These units are suitable for patients who are in relatively good general health, and do not need the services and care of a main renal unit.

For those having haemodialysis at home, initial treatment and training is given at a hospital dialysis unit. Haemodialysis at home has some advantages, including flexibility and not needing to rely on transport and not spending a great deal of time getting to and from the hospital. However, home haemodialysis may not be possible for some people who have complex needs and require close supervision, and it may affect others living at home and be stressful. There is also the need to store the haemodialysis equipment at home.

If there is no room for a dialysis machine at home, no carer or a need for medical supervision, then hospital or satellite haemodialysis is a better option. These options result in less flexibility as appointments need to fit in with the renal unit’s schedule and travelling to and from the renal unit can be very time consuming.

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How long does each haemodialysis treatment last for?

Most people need haemodialysis sessions 3 times a week, with each session lasting around 4 hours. During your dialysis sessions, you'll sit or lie on a couch, recliner or bed. You'll be able to read, listen to music, use your mobile phone or sleep.

After the dialysis session, the needles are removed and a plaster is applied to prevent bleeding. If you had haemodialysis in hospital, you can usually go home shortly afterwards.

Does haemodialysis hurt?

Haemodialysis may sting when the needles are inserted into the graft or fistula but this will go away very quickly once the needles are in place.

Haemodialysis itself is not painful but occasionally side effects do occur. These side effects may include dizziness, feeling sick (nausea), muscle cramps and general discomfort. These side effects may sometimes indicate that the haemodialysis needs to be adjusted or interrupted.

Further reading and references

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The information on this page is written and peer reviewed by qualified clinicians.

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