Pleural Effusion and Empyema

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Last modified 23/05/2015

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Pleural Effusion and Empyema

Anatomic Alterations of the Lungs

A number of pleural diseases can cause fluid to accumulate in the pleural space; this fluid is called a pleural effusion, or if infected, an empyema (see Figure 23-1). Similar to free air in the pleural space, fluid accumulation separates the visceral and parietal pleura and compresses the lungs. In severe cases, atelectasis will develop, the great veins may be compressed, and cardiac venous return may be diminished. Pleural effusion and empyema produce a restrictive lung disorder.

The major pathologic or structural changes associated with significant pleural effusion are as follows:

Etiology and Epidemiology

Pleural effusion affects approximately 1.3 million people each year in the United States. Early signs and symptoms include pleuritic chest pain, “chest pressure,” dyspnea, and cough. Chest pain can occur early when there is intense inflammation of the pleural surfaces. “Chest pressure” usually develops until the effusion is in the moderate (500 to 1500 mL) to large (>1500 mL) category. Dyspnea rarely occurs in small effusions unless significant pleurisy is present. A cough is usually directly related to the degree of atelectasis caused by the effusion.

A pleural effusion may be transudative or exudative. A transudate develops when fluid from the pulmonary capillaries moves into the pleural space. The fluid is thin and watery, containing a few blood cells and little protein. The pleural surfaces are not involved in producing the transudate. In contrast, an exudate develops when the pleural surfaces are diseased. The fluid has a high protein content and a great deal of cellular debris. Exudate is usually caused by inflammation, infection, or malignancy. Transudative pleural effusions and exudative pleural effusions are differentiated by comparing the chemistries of the pleural fluid with those of the blood. The pleural effusion is classified as exudative when one or more of the following is found in the pleural fluid:

Common Causes of Transudative Pleural Effusion

Congestive Heart Failure

Congestive heart failure is the most common cause of pleural effusion. Both right- and left-sided heart failure can result in pleural effusion. In general, left-sided heart failure is more likely to produce pleural effusion than right-sided heart failure. In right-sided heart failure (cor pulmonale), an increase in the hydrostatic pressure in the systemic circulation can (1) increase the rate of pleural fluid formation and (2) decrease lymphatic drainage from the pleural space because of the elevated systemic venous pressure. In left-sided heart failure, an increase in hydrostatic pressure in the pulmonary circulation can (1) decrease the rate of pleural fluid absorption through the visceral pleura and (2) cause fluid movement through the visceral pleura into the pleural space.

Common Causes of Exudative Pleural Effusion

Malignant Pleural Effusions

About two thirds of malignant pleural effusions occur in women. Malignant pleural effusions are highly associated with breast and gynecologic malignancies.

Other Pathologic Fluids That Separate the Parietal from the Visceral Pleura

In addition to transudate and exudate, other pathologic fluids can separate the parietal pleura from the visceral pleura.

Hemothorax

The presence of blood in the pleural space is known as a hemothorax. Most of these are caused by penetrating or blunt chest trauma. An iatrogenic hemothorax may develop from trauma caused by the insertion of a central venous or pulmonary artery catheter.

Blood can gain entrance into the pleural space from trauma to the chest wall, diaphragm, lung, or mediastinum. A hematocrit of the pleural fluid should always be obtained if the pleural fluid looks like blood. A hemothorax is said to be present only when the hematocrit of the pleural fluid is at least 50%.