Pleural Effusion

Pleural Effusion Summary
Pleural effusion is an excess fluid between the two membranes that envelop the lungs. There are two classifications of causes of pleural effusion; transudate and exudate. The treatment of pleural effusion depends on the cause.
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What is pleural effusion?

A pleural effusion is a collection of fluid in the space between the two linings (pleura) of the lung.

When we breathe, it is like a bellows. We inhale air into our lungs and the ribs move out and the diaphragm moves down. For the lung to expand, its lining has to slide along with the chest wall movement. For this to happen, both the lungs and the ribs are covered with a slippery lining called the pleura. A small amount of fluid acts as a lubricant for these two surfaces to slide easily against each other.

Too much fluid impairs the ability of the lung to expand and move.

Picture of pleural effusion
Picture of pleural effusion

What causes pleural effusion?

A pleural effusion is not normal. It is not a disease but rather a complication of an underlying illness. Extra fluid (effusion) can occur for a variety of reasons. Common classification systems divide pleural effusions based on the chemistry composition of the fluid and what causes the effusion to be formed. Two classifications are 1) transudate pleural effusions; and 2) exudate pleural effusions. Sometimes the pleural effusion can have characteristics of both a transudate and an exudate.

1. Transudate pleural effusions are formed when fluid leaks from blood vessels into the pleural space. Chemically, transudate pleural effusions contain less protein and LDH (lactate dehydrogenase) than exudate pleural effusions. If both the pleural fluid–to–serum total protein ratio is less than or equal to 0.50 and the pleural fluid–to–serum LDH ratios are less than or equal to 0.67, the fluid is usually considered to be a transudate while exudates ratios are above 0.50 and above 0.67.

Examples of transudate pleural effusions include:

2. Exudate pleural effusions are caused by inflammation of the pleura itself and are often due to disease of the lung.

Examples of exudate causes include:

Most pleural effusions are caused by congestive heart failure, pneumonia, pulmonary embolism and malignancy.

Medically Reviewed by a Doctor on 4/30/2014

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