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What are the pleura? Each lung is surrounded by a thin double-layered membrane called the pleura. The inner (visceral) layer is stuck to the outside of the lung, whereas the outer layer lines the inside of the chest wall. To help the lungs to continuously expand and contract with breathing, the tiny space between the two layers is filled by a small amount of fluid which acts as a lubricant allowing the two layers to slide easily over each other. The sharp pain of pleurisy is caused by inflamed and roughened pleural layers moving over each other. What is pleural fluid? In a healthy person there is a constant movement of water, body chemicals, and a small amount of protein into the pleural space from the outer layer. It is just as continuously being absorbed across the inner layer, draining back towards the centre of each lung through lymphatic channels which empty into the blood circulation. This is one way the lungs protect themselves against a constant bombardment of inhaled foreign particles. How does a pleural effusion occur? Pleural effusion is the term used to describe an abnormal accumulation of fluid in the pleural space. This can be caused by excessive production of fluid through the outer layer or reduced reabsorption across the inner layer. There are numerous causes of pleural effusion. Some causes of increased production of fluid include inflammation of the outer layer by infection and infiltration by tumour. Malnutrition leading to protein deficiency leads to a decreased ability to reabsorb fluid across the inner layer, as do certain types of heart disease; but, in all, there are over 30 different conditions which can lead to fluid accumulation in the pleural space. Symptoms The major symptom of pleural effusion is shortness of breath caused by compression of the lung as fluid builds up around it. Pain or cough caused by irritation of nerve fibres in the outer layer are relatively common, and other symptoms may occur related to the disease causing the effusion; eg. fever in infection, ankle swelling in heart disease, etc. Diagnosis The diagnosis of the presence of an effusion is usually very straightforward. A combination of symptoms, physical examination findings and a plain chest x-ray usually provides the diagnosis, but finding the cause of the effusion is often more difficult. There may be clear evidence of an underlying disease, but generally sampling of the fluid by inserting a small needle under local anaesthetic is necessary. Occasionally, CT scanning, bronchoscopy (using a flexible fibreoptic tube with a light on the end inserted into the bronchial tubes) or thoracoscopy are necessary. The latter is a procedure, usually performed by a surgeon, under general anaesthesia, through a small incision using a telescope-like instrument to examine the inside of the chest and take biopsies if necessary. Treatment The treatment of pleural effusion is the treatment of the underlying cause. Occasionally it is necessary to completely drain the fluid from the pleural space, and this can be done through a tube which can be inserted and left in the pleural space, sometimes for a number of days to ensure that the space is completely dry. Occasionally it is then necessary to instil a chemical through the tube to prevent further fluid from gathering. sometimes this can only be done by an operation, as detailed above. Please Note: This information is intended by The Australian Lung Foundation to be used as a guide only and is not an authoritative statement. Please consult your family doctor or specialist respiratory physician if you have further questions relating to the information provided here.
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