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  • • Asymptomatic in many cases; pleuritic chest pain if pleuritis is present; dyspnea if effusion is large.
  • • Diminished breath sounds; decreased tactile fremitus; dullness to percussion; egophony if effusion is large.
  • • Radiographic evidence of pleural effusion.
  • • Diagnostic findings on thoracentesis.

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In the healthy human being the surfaces of the pleural cavity are coated with a surfactant-containing, hypooncotic fluid that lubricates, allowing frictionless apposition of the parietal and visceral pleura during the respiratory cycle. Under normal conditions approximately 0.2–0.3 mL/kg of pleural fluid is present in the pleural space. Its continuous turnover represents a balance between production by the systemic vessels of the pleura (primarily the capillaries of the less dependent portions of the parietal pleura) and removal by the pleural lymphatics (largely in the more dependent portions of the parietal pleura). The rate of production of pleural fluid under homeostatic conditions is estimated to be 0.01 mL/kg/h and is governed by the permeability of the pleural vessels and the balance of hydrostatic and oncotic gradients across the pleural surfaces. Normal pleural fluid is low in protein (∼1 g/dL), slightly alkaline compared to serum, and relatively hypocellular with approximately 2000 white blood cells (WBC)/ μL in a monocyte/macrophage predominance with 10–20% lymphocytes and a few granulocytes and erythrocytes.

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Pleural effusion is an abnormal collection of fluid in the pleural space. Effusions, which may arise from a wide variety of pathological conditions, are typically classified as empyematous, hemorrhagic, chylous, exudative, or transudative. Whereas the first three categories denote collections of pus (from thoracic infection), blood (as in hemothorax), or lipid-rich chyle (from the chylous duct), the last two represent broader categories of pathogenesis. Exudative effusions are protein rich and often quite cellular, typically reflecting inflammatory or infiltrative processes directly affecting the pleura (such as pneumonia or cancer), whereas transudative effusions are low-protein, acellular filtrates that usually arise from imbalances in the body’s hydrostatic and/or oncotic forces in the setting of otherwise normal pleura (such as occur in congestive heart failure or nephrotic syndrome). Causes of transudative and exudative effusions are listed in Table 22–1.

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Table Graphic Jump Location
Table 22–1. Causes of Transudative and Exudative Pleural Effusions.
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Symptoms and Signs

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The hallmarks of pleural effusion on physical examination are diminution of breath ...

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