Inside the abdomen is a membrane called the peritoneum, which has two layers. One layer lines the abdominal wall and the other layer covers the organs inside the abdominal cavity. The peritoneum produces a fluid that acts as a lubricant and allows the abdominal organs to glide smoothly over one another. Sometimes too much of this fluid can build up between the two layers and this is called ascites.

Ascites can be a symptom of many types of cancer. The types of cancer that are more likely to cause ascites are cancer of the breast, lung, large bowel (colon), stomach, pancreas, ovary and the lining of the womb (endometrium).

There may be several reasons for the build-up of ascites:

• If cancer cells have spread to the lining of the abdomen, they can irritate it and cause fluid to build up.
• If the liver is affected by cancer cells, this may block the circulation of blood through the liver, which can lead to a build-up of fluid in the abdomen.
• If the liver is damaged, it may produce less blood protein. This may upset the body's fluid balance, which causes fluid to build up in the body tissues, including the abdomen.
• Cancer cells can block the lymphatic system. The lymphatic system is a network of fine channels which runs throughout the body. One of its functions is to drain off excess fluid, which is eventually got rid of in the urine. If some of these lymphatic channels are blocked, the system cannot drain efficiently and fluid can build up.

The symptoms of ascites can be very distressing. The abdomen becomes very swollen and distended, which can be uncomfortable or painful. It can also cause difficulty in getting comfortable, sitting up or walking. It can make you feel very tired (lethargic) and breathless. It may cause feelings of sickness (nausea) or make you sick (vomiting). You may also suffer indigestion and a reduced appetite.

In order to relieve symptoms, the treatment of ascites involves slowing the build-up of the fluid and putting a tube into the abdomen to drain it (known as paracentesis).

The ascitic tube (drain) is usually inserted by a doctor and the procedure can be done at the bedside in the ward or in the outpatients clinic. Sometimes the drain may be inserted in the ultrasound department whilst scanning the abdomen. This helps the doctor find exactly where to put the drain, especially if the fluid appears to be in small pockets and cannot be drained all at once.

You will be asked to lie on the bed while the skin in the area where the drain is to be inserted is cleaned with an antiseptic solution, which prevents it from becoming infected. The doctor then gives an injection of local anaesthetic into the area to prevent the procedure from being painful.

When the area has been anaesthetised, the doctor makes a very small cut in the skin of the abdomen and inserts a thin tube called a cannula. The cannula is attached to a tube and drainage bag. The ascitic fluid drains out of the abdomen and collects inside the drainage bag. The cannula may be held in place with a couple of stitches and covered with a dressing.

The length of time that the drainage tube needs to stay in place depends on the amount of fluid that needs to be drained off. Sometimes a small amount of fluid can be drained in the outpatients clinic. If there is a large amount of fluid however, the procedure may need to be carried out in hospital under the supervision of the doctors and nurses, and the drain may stay in place for a period of 2–3 days.

It is possible for the ascites to build up again and drainage may need to be carried out more than once.

Usually the fluid will be drained off slowly, as a sudden release of pressure in the abdomen can cause a drop in blood pressure. A litre of fluid may be drained safely as soon as the drain has been inserted. After this, the drainage will usually be done more slowly. Your blood pressure will be checked during the procedure.

The ascitic drain can become blocked. This can sometimes be cleared by changing your position or sitting upright. Occasionally the tube may need to be replaced.

The drain can sometimes become infected and you will have your temperature taken regularly as a high temperature can be a sign of infection.

When the drain has been removed, there may be a leakage of fluid from the drain site until the hole heals. The hole will be stitched together and the site will need to be covered with a dressing or drainage bag until the leakage has stopped. Usually the stitches are taken out after about a week.

The doctors may prescribe a water tablet (diuretic) called spironolactone (Aldactone®). This can make you want to pass more urine than normal but will slow the build-up of the ascitic fluid.

A peritoneo-venous shunt (sometimes called a LeVeen shunt) may be considered. A shunt is a plastic or silicone rubber tube that is placed into the peritoneal cavity and drains the ascitic fluid directly into a large vein. This is a more complicated procedure and usually needs to be done under a general anaesthetic. You will also need intensive monitoring for the first 24–48 hours in a high dependency unit at the hospital, in order to check that the shunt is working properly. The shunt stays in permanently.

This section has been compiled using information from a number of reliable sources, including:

• Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
• Cancer and Its Management (5th edition). Souhami and Tobias. Oxford Blackwell Scientific Publications, 2005.
• Symptom Management in Advanced Cancer (3rd edition). Twycross and Wilcock. Radcliffe Medical Press, 2001.

For further references, please see the general bibliography.