PLEURAL EFFUSION

6. What is a pleural effusion?

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Pleural fluid is generated in normal adults at a rate of 5-10 L per 24 hours in the combined hemithoraces, but normal adults have only 20 mL of pleural fluid present at any time. Pleural effusions develop when there is either increased production or decreased resorption. Pathologic conditions leading to effusions include increased capillary permeability (inflammation, tumor), increased hydrostatic pressure (e.g., in congestive heart failure [CHF]), decreased lymphatic drainage (tumor, radiation fibrosis), decreased oncotic pressure (hypoalbuminemia), or combinations of these.

7. How does one determine the cause of a pleural effusion?

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History and physical examination, chest radiograph (upright and decubitus), and thoracentesis are used. Thoracentesis should be used to evaluate the pleural fluid. Bloody fluid is typical of trauma, pulmonary embolism, malignancy, milky fluid with chylothorax (triglyceride > 110), and purulent fluid with empyema. Fluid should be checked for cell count; cytology; pH; Gram stain; culture; and glucose, protein, lactate dehydrogenase (LDH), amylase, and triglyceride level. Exudates have a protein ratio > 0.5 and an LDH ratio > 0.6. The most common cause of transudate is CHF; the most common cause of exudate is malignancy and infection. Glucose < 60 mg/dL is seen in only parapneumonic effusions, rheumatoid effusion, tuberculous pleuritis, and malignancy.

8. What is the management of a pleural effusion?

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Thoracentesis or a tube thoracostomy should be used to evacuate the effusion completely. The underlying problem (e.g., CHF) should be corrected if possible. If the effusion is persistent (e.g., malignancy), then pleurodesis (stick the parietal and visceral pleurae together) can be performed with sclerosants (talc) or mechanical abrasion. Pleural symphysis (stuck pleura) results in decreased surface area for production, eliminates the pleural space for accumulation, and prevents lung collapse and compression. Chest tubes are generally removed when output is < 75 mL per 24 hours.

9. What does an air-fluid level on an initial chest radiograph indicate?

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An air-fluid level before any drainage procedure may represent a bronchopleural fistula. These fistulas may resolve with chest tube drainage or require open thoracotomy for definitive repair.