Pleural Effusion



Accumulation of fluid in the pleural cavity


  • Normally 1 to 15 mL of fluid in the pleural space
  • Alterations in the flow and/or absorption of this fluid lead to its accumulation.
  • Mechanisms that influence this flow of fluid:
    • Increased capillary hydrostatic pressure (i.e., congestive heart failure [CHF], overhydration)
    • Decreased pleural space hydrostatic pressure (i.e., after thoracentesis, atelectasis)
    • Decreased plasma oncotic pressure (i.e., hypoalbuminemia, nephrosis)
    • Increased capillary permeability (i.e., infection, toxins, connective tissue diseases, malignancy)
    • Impaired lymphatic drainage from the pleural space (i.e., disruption of the thoracic duct)
    • Passage of fluid from the peritoneal cavity through the diaphragm to the pleural space (i.e., hepatic cirrhosis with ascites)
  • Two types of pleural effusion:
    • Transudate: Mechanical forces of hydrostatic and oncotic pressures are altered, favoring liquid filtration.
    • Exudate: Damage to the pleural surface occurs that alters its ability to filter pleural fluid; lymphatic drainage is diminished.
  • Stages associated with parapneumonic effusions (infectious exudates):
    • See “Appendix, Table 3.”
    • Exudative stage
      • Free-flowing fluid
      • Pleural fluid glucose, protein, lactate dehydrogenase (LDH) level, and pH are normal.
    • Fibrinolytic stage
      • Loculations are forming.
      • Increase in fibrin, polymorphonuclear leukocytes, and bacterial invasion of pleural cavity are occurring.
      • Pleural fluid glucose and pH falls, whereas protein and LDH levels increase.
    • Organizing stage (empyema)
      • Fibroblasts grow.
      • Pleural peal forms.
      • Pleural fluid parameters worsen.

There's more to see -- the rest of this topic is available only to subscribers.