DESCRIPTION

Pathologic accumulation of fluid in the pleural cavity

PATHOPHYSIOLOGY

• Normally 1 to 15 mL (0.25 mL/kg) of fluid in the pleural space
• Alteration in the flow and/or absorption of this fluid leads to its accumulation.
• Mechanisms that influence this flow of fluid:
  • Increased capillary hydrostatic pressure (congestive heart failure [CHF])
  • Decreased pleural space hydrostatic pressure (after thoracentesis, atelectasis)
  • Decreased plasma oncotic pressure (hypoalbuminemia, nephrotic syndrome)
  • Increased capillary permeability (infection, toxins, connective tissue diseases, malignancy)
  • Impaired lymphatic drainage from the pleural space (disruption or blockage of the thoracic duct causing a chylous effusion)
  • Passage of fluid from the peritoneal cavity through the diaphragm to the pleural space (hepatic cirrhosis with ascites)
• Two types of pleural effusion:
  • Transudate: due to alteration in mechanical forces of hydrostatic and oncotic pressures, favoring liquid filtration into the pleural space (clear or straw-colored fluid)
  • Exudate: due to increased capillary permeability (cloudy, may be purulent)
• Most common cause of pleural effusion in children is due to pneumonia (parapneumonic effusion).
  • As these effusions mature, they become organized and fibrotic and may form a thick peel resulting in lung restriction (see Appendix IV, Table 3).