Pleural Effusion
Fluid accumulates in the pleural space when the normal balance between fluid formation and pleural lymphatic drainage is disrupted, and whether that imbalance is from raised hydrostatic/low oncotic pressure (transudate) or local pleural or lung pathology (exudate) determines both the underlying cause and the diagnostic pathway.
In a nutshell
An effusion forms when pleural fluid formation outpaces lymphatic drainage. A transudate reflects a systemic pressure problem (heart failure, hypoalbuminaemia) across intact pleura; an exudate reflects local pleural or lung disease (infection, malignancy, PE) with leaky capillaries. Light's criteria distinguish the two and direct the search for cause; a low pleural fluid pH means drainage, not antibiotics alone.
Classic presentation
Progressive breathlessness with reduced chest expansion, stony dull percussion and reduced breath sounds over one lung base, in a patient with heart failure, liver disease, infection or malignancy.
Key points
- Transudates form across intact pleura from systemic hydrostatic/oncotic pressure changes (heart failure, hypoalbuminaemia); exudates form from local pleural/lung inflammation making capillaries leaky.
Educational content pending clinical review. Not medical advice.