Pleural Effusion
Fluid in the pleural space can reflect systemic pressure changes, infection, malignancy, pulmonary embolism or other disease; the safe pathway is clinical assessment, ultrasound-guided classification and cause-directed treatment with urgent drainage when pleural infection is high risk.
Definition
A pleural effusion is an abnormal collection of fluid in the pleural space. It may be transudative from systemic hydrostatic or oncotic changes or exudative from local pleural, pulmonary, infective, malignant or vascular disease.
First principles
An effusion forms when production exceeds pleural clearance
Pleural fluid normally remains a thin lubricating layer. An effusion develops when hydrostatic or oncotic forces change, local inflammation increases permeability, tumour obstructs lymphatic drainage or another process overwhelms clearance. The mechanism narrows the differential but does not replace fluid analysis or imaging when the cause is uncertain.
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