Dialysis - How haemodialysis and peritoneal dialysis are performed

Haemodialysis and peritoneal dialysis are two types of dialysis carried out in different ways.

Haemodialysis

If you decide to have haemodialysis, the first step usually involves creating an arteriovenous fistula (AV fistula). This is a surgically modified blood vessel created by connecting an artery to a vein. The fistula will usually be created in your wrist and upper arm.

Creating a fistula by 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 six 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. This involves using a piece of synthetic tubing (graft) to connect an artery to a vein.

As a short-term measure, or if haemodialysis is suddenly required due to a medical emergency, you may be given a neck line. This is where a small tube is inserted into a vein in your neck. Once the AV fistula has been created and has had time to heal, the neck line can be removed.

The haemodialysis process

Most people require three sessions of haemodialysis a week with each session lasting four hours. A dialysis session takes at least four hours to complete because your blood needs to be removed and then replaced slowly.

At the start of the session, your blood pressure, skin temperature and pulse will be measured. If you decide to have dialysis at home, you will be trained to take these measurements 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 ‘dirty’ dialysate fluid is pumped out of the dialyser and the ‘clean’ blood is passed back into your body through the second needle.

It would be too dangerous to remove large amounts of blood in one go, so only 40-50ml (two fluid ounces) of blood is removed at any one time.

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. Children who have haemodialysis often find that playing on a mobile games console is an enjoyable way to pass the time.

Haemodialysis is not painful, but some people experience symptoms of nausea, dizziness and muscle cramps during the procedure. This is caused by the rapid changes in blood fluid levels that occur during dialysis.

After the dialysis session, the needles are removed and a plaster is applied to prevent bleeding.

Haemodialysis and fluid intake

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

This is because your kidneys are not working properly. The haemodialysis process itself also limits the amount of fluid you can drink.

Over the course of a day, healthy kidneys constantly remove excess fluid from the body. However, during the haemodialysis process, two to three days' worth of fluid is removed over the course of four hours.

If you drink too much, the dialyser will be unable to remove all of the fluid and excess fluid will build up in your blood, tissues and lungs. This can be serious and lead to:

• breathing difficulties
• high blood pressure (hypertension)
• coronary heart disease – a condition where the blood supply to the heart muscles becomes restricted

The amount of fluid you are 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 will also need to avoid eating foods that have a high fluid content, such as:

• soup
• ice cream
• melons
• oranges
• tomatoes

Many people having haemodialysis find that the restriction on drinking fluids is one of the most challenging aspects of living with dialysis. Chewing gum or sucking an ice cube may help alleviate your symptoms of thirst.

Haemodialysis and diet

As well as removing waste products, your kidneys help regulate the amount of minerals in your body, including:

• sodium (salt)
• potassium
• phosphorus

These minerals are removed during haemodialysis. However, the levels of each mineral can quickly build up between dialysis sessions, particularly if you eat foods high in potassium, phosphorus or sodium.

Excess levels of any of these minerals can be dangerous and lead to:

• seizures (fits) and coma
• osteoporosis (weakness of the bones)
• an irregular heart beat (arrhythmia)
• in the most serious cases, sudden death 

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

Foods high in salt include:

• ready-to-eat meals (including ready-to-eat sandwiches)
• bacon
• ham
• smoked fish
• cheese

Foods high in potassium include:

• bananas
• baked potatoes
• oranges
• chocolate

Foods high in phosphorus include:

• dairy products, such as cheese
• yoghurt
• baked beans
• lentils
• sardines
• bran cereals

Peritoneal dialysis

As with haemodialysis, the first stage in peritoneal dialysis is to create an access point. This is so that the dialysate fluid can pass through your peritoneal cavity (the space surrounding your peritoneum, a thin membrane lining the inside of the abdomen).

To create an access point, an incision is made in your abdomen, usually just below your navel (belly button). A piece of equipment called a Tenckhoff catheter will be inserted into the incision.

A Tenckhoff catheter is a thin piece of tube, about 10cm (four inches) long. The dialysate fluid is passed through the catheter and into the peritoneal cavity. After a dialysis session is complete, the end of the catheter is sealed. You will be shown how to keep the catheter clean to prevent peritonitis (infection of the peritoneum).

The Tenckhoff catheter is permanently attached to your abdomen, which many people find upsetting. If you are unable to get used to the catheter, you can have it removed and you can switch to haemodialysis.

Types of peritoneal dialysis

There are two main types of peritoneal dialysis. They are:

• continuous ambulatory peritoneal dialysis (CAPD) – where your blood is filtered several times during the day
• automated peritoneal dialysis (APD) – where a machine filters your blood during the night as you sleep

Continuous ambulatory peritoneal dialysis

The equipment used to carry out CAPD consists of:

• a bag containing the 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 both bags from

CAPD involves exchanging old dialysate fluid that contains waste products and excess fluids with new dialysate fluid.

An exchange begins by draining the old fluid into the waste bag. The new fluid is then drained into your peritoneal cavity. The process is painless and takes about 30-40 minutes to complete.

The new fluid is left in the peritoneal cavity for a number of hours (you will be advised about what the best length of time for you is).

As blood passes through the peritoneum, special chemicals in the dialysate fluid draw out waste products and excess fluid from the blood into the fluid. After the set time has passed, you will begin the process again, exchanging the old fluid for the new fluid. Most people who use CAPD require four exchanges a day.

You will be fully trained in how to carry out both types of draining, and will be given detailed instructions about how to keep all of the equipment clean to prevent peritonitis.

Automated peritoneal dialysis (APD)

Automated peritoneal dialysis (APD) works on the same principles as CAPD, except that a machine is used to control the drainage of fluid. You fill the APD machine with fluid before you go to bed. As you sleep, the machine automatically performs a number of exchanges.

You will usually need to be attached to the APD machine for 8-10 hours. You will then usually have one last fill of fluid that is kept in your cavity all day before it is drained away the following evening. 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 will be given the telephone number of a 24-hour hotline that you can use in case you experience any technical problems. 

Dialysis and pregnancy

If you become pregnant while having dialysis, it is usually recommended that you are treated with haemodialysis at a dialysis unit (if you are not being treated already). This will enable your condition to be regularly monitored.

Research has found that pregnant women who are treated with haemodialysis have a healthier pregnancy than women who are treated with peritoneal dialysis.

It is likely that the number of haemodialysis sessions will need to be increased as a precaution to protect the baby from any waste products in your blood. Most pregnant women require five to six sessions a week, rather than the three sessions that most people have.

Equipment

If you are having home haemodialysis or peritoneal dialysis, it is important that you keep additional supplies of equipment in case of an emergency, such as adverse weather conditions that prevent you from obtaining supplies.

It is recommended that you keep at least a week’s worth of equipment as an emergency backup supply. You should also let your electrical company know if you are 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.