Normally, the pleural space contains a small amount of extracellular fluid that lubricates the pleural surfaces. But if fluid builds up from either increased production or inadequate removal, pleural effusion results. An accumulation of pus and necrotic tissue in the pleural space results in empyema, a type of pleural effusion. Blood (hemothorax) and chyle (chylothorax) may also collect in this space.

The incidence of pleural effusion increases with heart failure (the most common cause), parapneumonia, cancer, and pulmonary embolism.

Pleural effusion may be transudative or exudative. (See What causes pleural effusion?)

Empyema usually stems from an infection in the pleural space. The infection may be idiopathic or may be related to pneumonitis, cancer, perforation, penetrating chest trauma, or esophageal rupture.

Large pleural effusions may result in atelectasis, infection, and hypoxemia.

The patient’s history characteristically shows underlying pulmonary disease. If he has a large amount of effusion, he’ll typically complain of dyspnea. If he has pleurisy, he may report pleuritic chest pain. If he has empyema, he may also complain of a general feeling of malaise.

Inspection may indicate that the trachea has deviated away from the affected side. With empyema, the patient may also have a fever.

On palpation, you may note decreased tactile fremitus with a large amount of effusion. Percussion may disclose dullness over the effused area that doesn’t change with respiration.

When you auscultate the chest, you may hear diminished or absent breath sounds over the effusion and a pleural friction rub during inspiration and expiration. (This pleural friction rub is transitory, however, and disappears as fluid accumulates in the pleural space.) You’ll also hear bronchial breath sounds, sometimes with the patient’s pronunciation of the letter E sounding like the letter A.

Chest X-rays show radiopaque fluidindependent regions (usually with fluid accumulation of more than 250 ml). Thoracentesis allows analysis of aspirated fluid and may show the following: