Pleural Effusion

A pleural effusion is a collection of fluid in the pleural cavity. This can be exudative meaning there is a high protein count (>3g/dL) or transudative meaning there is a relatively lower protein count (<3g/dL). Whether it is exudative or transudative helps determine the cause.


Exudative Causes

Exudative causes are related to inflammation. The inflammation results in protein leaking out of the tissues in to the pleural space (ex- meaning moving out of). Think of the causes of inflammation:

  • Lung cancer
  • Pneumonia
  • Rheumatoid arthritis
  • Tuberculosis

Transudative Causes

Transudative causes relate to fluid moving across into the pleural space (trans- meaning moving across). Think of the causes of fluid shifting:

  • Congestive cardiac failure
  • Hypoalbuminaemia
  • Hypothroidism
  • Meig’s syndrome (right sided pleural effusion with ovarian malignancy)


  • Shortness of breath
  • Dullness to percussion over the effusion
  • Reduced breath sounds
  • Tracheal deviation away from the effusion if it is massive


Chest xray shows:

  • Blunting of the costophrenic angle
  • Fluid in the lung fissures
  • Larger effusions will have a meniscus. This is a curving upwards where it meets the chest wall and mediastinum.
  • Tracheal and mediastinal deviation if it is a massive effusion

Taking a sample of the pleural fluid by aspiration or chest drain is required to analyse it for protein count, cell count, pH, glucose, LDH and microbiology testing.


Conservative management may be appropriate as small effusions will resolve with treatment of the underlying cause. Larger effusions often need aspiration or drainage.

Pleural aspiration involves sticking a needle in and aspirating the fluid. This can temporarily relieve the pressure but the effusion may recur and repeated aspiration may be required.

Chest drain can be used to drain the effusion and prevent it recurring.


Empyema is where there is an infected pleural effusion. Suspect an empyema in a patient who has an improving pneumonia but new or ongoing fever. Pleural aspiration shows pus, acidic pH (pH < 7.2), low glucose and high LDH. Empyema is treated by chest drain to remove the pus and antibiotics.


Last updated March 2019
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