Pleural Effusions

Pleural effusion is a condition in which excess fluid accumulates in the pleural cavity. Typically, the pleural cavity is filled with a small amount of pleural fluid, however, the pleural cavity has the potential of accumulating large amounts of fluid.

In general, 3 mechanisms can lead to pleural effusions:

1. Increased drainage of fluid into pleural space
2. Increased production of fluid by cells in the pleural space
3. Decreased drainage if fluid from the pleural space.

As seen in this Daily Doodle, pleural effusions can be divided into two main categories: exudative and transudative effusions.

Exudative effusions, located on the top left hand corner of the doodle, are usually caused by local factors that change the pleural surface permeability, such as:

      • Infection (25%): bacterial pneumonia, tuberculosis, viral infections
      • Malignancy, metastatic disease (15%)
      • Pulmonary embolism (10%)
      • Collagen vascular disease

Transudative effusions, located on the bottom right hand corner of the doodle, are typically caused by systemic factors which cause a decrease in oncotic pressure or increased pulmonary capillary wedge pressure (hydrostatic pressure). Examples of transudative effusions include:

      • Congestive heart failure (40%)
      • Constrictive pericarditis
      • Pulmonar Embolism
      • Cirrhosis
      • Nephrotic syndrome
      • Hypoalbuminemia
      • Atelectasis

Note: PE can cause both transudative and exudative pleural effusions.

Although often asymptomatic, symptoms include dyspnea on exertion, paroxysmal nocturnal dyspnea, and orthopnea.



  1. M. Sabatine “Pocket Medicine” Fourth Edition. Lippincott Williams & Wilkins. 2011.
  2. S. Agabegi and E. Agabegi. “Step-Up to Medicine” Lippincott Williams & Wilkins. 2013.


“Pleural Effusion” Daily Doodle by Michiko Maruyama, UBC NMP

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