How dialysis is performed 

There are two main types of dialysis: haemodialysis and peritoneal dialysis.

  • Haemodialysis involves diverting blood into an external machine, where it's filtered before being returned to the body
  • Peritoneal dialysis involves pumping dialysis fluid into the space inside your abdomen (tummy) to draw out waste products from the blood passing through vessels lining the inside of the abdomen

These two treatments are outlined in more detail below.


Preparing for treatment

Before haemodialysis can start, you'll usually need to have a special blood vessel created in your arm, called an arteriovenous fistula (AV fistula). This blood vessel is created by connecting an artery to a vein.

Joining a vein and an artery together makes the blood vessel larger and stronger. This makes it easier to transfer your blood into the dialysis machine and back again.

The operation to create the AV fistula is usually carried out around four to eight weeks before haemodialysis begins. This allows the tissue and skin surrounding the fistula to heal.

If your 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 (graft) is used to connect the artery to the vein.

As a short-term measure, or in an emergency, you may be given a neck line. This is where a small tube is inserted into a vein in your neck.

The haemodialysis process

Most people need three sessions of haemodialysis a week, with each session lasting around four hours. This can be done in hospital, or at home if you've been trained to do it yourself.

Two thin needles will be inserted into your AV fistula or graft and taped into place. One needle will slowly remove blood and transfer it to a machine called a dialyser or dialysis machine.

The dialysis machine is made up of a series of membranes that act as filters and a special liquid called dialysate.

The membranes filter waste products from your blood, which are passed into the dialysate fluid. The used dialysate fluid is pumped out of the dialyser and the filtered blood is passed back into your body through the second needle.

During your dialysis sessions, you will sit or lie on a couch, recliner or bed. You will be able to read, listen to music, use your mobile phone or sleep.

Haemodialysis isn't painful, but some people feel a bit sick and dizzy, and may have muscle cramps during the procedure. This is caused by the rapid changes in blood fluid levels that occur during the treatment.

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

Fluid and diet restrictions

If you're having haemodialysis, the amount of fluid you can drink will be severely restricted.

This is because the dialysis machine won't be able to remove two to three days' worth of excess fluid from your blood in four hours if you drink too much. This can lead to serious problems where excess fluid builds up in your blood, tissues and lungs.

The amount of fluid you're allowed to drink will depend on your size and weight. Most people are only allowed to drink 1,000-1,500ml (two to three pints) of fluid a day.

You'll also need to be careful what you eat while having haemodialysis because minerals such as sodium (salt), potassium and phosphorus that would normally be filtered out by your kidneys can build up to dangerous levels quickly between treatment sessions.

You'll be referred to a dietitian so a suitable diet plan can be drawn up for you. Diet plans differ from person to person, but it's likely you'll be asked to avoid eating foods high in potassium and phosphorus and to cut down the amount of salt you eat.

Peritoneal dialysis

There are two main types of peritoneal dialysis:

Both treatments can be done at home once you've been trained to carry them out yourself. They're described in more detail below.

Preparing for treatment

Before you can have CAPD or APD, an opening will need to be made in your abdomen. This will allow the dialysis fluid (dialysate) to be pumped into the space inside your abdomen (the peritoneal cavity).

An incision is usually made just below your belly button. A thin tube called a catheter is inserted into the incision and the opening will normally be left to heal for a few weeks before treatment starts.

The catheter is permanently attached to your abdomen, which some people find difficult. If you're unable to get used to the catheter, you can have it removed and switch to haemodialysis instead.

Continuous ambulatory peritoneal dialysis

The equipment used to carry out CAPD consists of:

  • a bag containing dialysate fluid
  • an empty bag used to collect waste products
  • a series of tubing and clips used to secure both bags to the catheter
  • a wheeled stand that you can hang the bags from

At first, the bag containing dialysate fluid is attached to the catheter in your abdomen. This allows the fluid to flow into the peritoneal cavity, where it's left for a few hours.

While the dialysate fluid is in the peritoneal cavity, waste products and excess fluid in the blood passing through the lining of the cavity are drawn out of the blood and into the fluid.

A few hours later, the old fluid is drained into the waste bag. New fluid from a fresh bag is then passed into your peritoneal cavity to replace it, and left there until the next session. This process of exchanging the fluids is painless and usually takes about 30-40 minutes to complete.

Exchanging the fluids isn't painful, but you may find the sensation of filling your abdomen with fluid uncomfortable or strange at first. This should start to become less noticeable as you get used to it.

Most people who use CAPD need to repeat this around four times a day. Between treatment sessions, the bags are disconnected and the end of the catheter is sealed. 

Automated peritoneal dialysis (APD)

Automated peritoneal dialysis (APD) is similar to CAPD, except a machine is used to control the exchange of fluid while you sleep.

You attach a bag filled with dialysate fluid to the APD machine before you go to bed. As you sleep, the machine automatically performs a number of fluid exchanges.

You'll usually need to be attached to the APD machine for 8-10 hours. At the end of the treatment session, some dialysate fluid will be left in your abdomen. This will be drained during your next session.

During the night, an exchange can be temporarily interrupted if, for example, you need to get up to go to the toilet.

Some people who have APD worry that a power cut or other technical problem could be dangerous. However, it is usually safe to miss one night’s worth of exchanges as long as you resume treatment within 24 hours. You'll be given the telephone number of a 24-hour hotline you can call if you experience any technical problems. 

Fluid and diet restrictions

If you're having peritoneal dialysis, there are generally fewer restrictions on diet and fluid intake compared with haemodialysis because the treatment is carried out more often.

However, you may sometimes be advised to limit how much fluid you drink and you may need to make some changes to your diet. A dietitian will discuss this with you if appropriate.

Dialysis and pregnancy

Becoming pregnant while on dialysis can sometimes be dangerous for the mother and baby.

It's possible to have a successful pregnancy while on dialysis, but you'll probably need to be monitored more closely at a dialysis unit and you may need more frequent or longer treatment sessions.

If you're considering trying for a baby, it's a good idea to discuss this with your doctor first. 

Dialysis equipment

If you're having home haemodialysis or peritoneal dialysis, the supplies and equipment you need will normally be provided by your hospital or dialysis clinic.

You'll be told how to get and store your supplies as part of your training in carrying out the procedure.

It's important to make sure you have enough supplies of equipment in case of an emergency, such as adverse weather conditions that prevent you from obtaining supplies. Your doctor or nurse may suggest keeping at least a week's worth of equipment as an emergency backup supply.

You should also let your electrical company know if you're using home haemodialysis or automated peritoneal dialysis. This is so they can treat you as a priority in the event that your electrical supply is disrupted.

Page last reviewed: 07/07/2015

Next review due: 07/07/2017