Pleural Effusion

Posted by e-Medical PPT Wednesday, December 1, 2010
Pleural effusion is excess fluid that accumulates in the pleura, the fluid-filled space that surrounds the lungs.Pleural effusion is usually diagnosed on the basis of medical history and physical exam, and confirmed by chest x-ray. Once accumulated fluid is more than 500 ml, there are usually detectable clinical signs in the patient, such as decreased movement of the chest on the affected side, stony dullness to percussion over the fluid, diminished breath sounds on the affected side, decreased vocal resonance and fremitus (though this is an inconsistent and unreliable sign), and pleural friction rub.
Once a pleural effusion is diagnosed, the cause must be determined. Pleural fluid is drawn out of the pleural space in a process called thoracentesis. A needle is inserted through the back of the chest wall in the sixth, seventh, or eighth intercostal space on the midaxillary line, into the pleural space.
An accurate diagnosis of the cause of the effusion, transudate versus exudate, relies on a comparison of the chemistries in the pleural fluid to those in the blood, using Light's criteria. According to Light's criteria, a pleural effusion is likely exudative if at least one of the following exists:
   1. The ratio of pleural fluid protein to serum protein is greater than 0.5
   2. The ratio of pleural fluid LDH and serum LDH is greater than 0.6
   3. Pleural LDH is greater than 200
   4. Pleural fluid LDH is greater than 0.6 or times the normal upper limit for serum.
The most common causes of transudative pleural effusions in the United States are left ventricular failure,cirrhosis and nephrotic syndrome.
The most common causes of exudative pleural effusions are bacterial pneumonia, cancer (with lung cancer, breast cancer, and lymphoma causing approximately 75% of all malignant pleural effusions), viral infection, and pulmonary embolism.

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