PassFinals
Respiratory

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.

In a nutshell

A pleural effusion is fluid in the pleural space. Assess severity and cause with chest imaging and ultrasound-guided fluid sampling when indicated; use Light's criteria to separate transudative from exudative patterns. Infection needs prompt pH-based risk assessment and drainage when high risk, while malignant effusion treatment depends on symptoms, lung expansion, prognosis and patient preference.

Classic presentation

Progressive breathlessness with reduced expansion, stony dullness and reduced breath sounds at a lung base, with cardiac, hepatic, renal, infective or malignant context.

Key points

  • A typical bilateral heart-failure effusion may improve with treatment of congestion; sample or investigate atypical, unilateral, febrile or non-resolving fluid.
  • Use thoracic ultrasound to confirm fluid and guide aspiration or drain insertion.
  • Light's criteria classify transudative versus exudative fluid but do not identify the final cause.
  • Frank pus or pleural pH at or below 7.20 is high risk for pleural infection and supports intercostal drainage when safe accessible fluid is present.
  • Intermediate pleural pH needs LDH and the wider clinical, biochemical, ultrasound and CT picture; a single number is not the whole decision.
  • Recurrent malignant effusion needs an individualized pleurodesis or indwelling-pleural-catheter plan, especially if the lung is non-expandable.
  • Persistent infection, loculation, trapped lung or unexplained exudate needs early specialist pleural review.

First-line investigation

Chest X-ray and thoracic ultrasound, followed by ultrasound-guided diagnostic aspiration with paired serum and pleural protein/LDH and cause-directed testing when appropriate.

Management

Assess severity and infection

  • Assess oxygenation, sepsis, haemodynamic compromise and pulmonary-embolism or malignancy red flags; seek urgent pleural or respiratory input for severe breathlessness or suspected pleural infection.1,6

Image and classify

  • Confirm fluid with chest imaging and ultrasound, then use ultrasound-guided aspiration with paired serum and pleural protein and LDH plus pH, microbiology and cytology when indicated.1,4

Treat the cause

  • Treat systemic congestion or the identified cause, and use therapeutic aspiration selectively for symptomatic relief rather than as a substitute for diagnosis and cause-directed management.1,2

Drain infection or recurrent malignant fluid

  • Drain high-risk pleural infection when safe accessible fluid is present; discuss specialist intrapleural or surgical escalation if source control fails, and individualize malignant-effusion intervention by lung expansion and preference.4,7,3

Reassess and safety-net

  • Review symptoms, imaging, drain function, recurrence and the final diagnosis; provide a named respiratory or pleural follow-up plan and urgent advice for worsening breathlessness, fever, chest pain, hypoxia or bleeding.1,6

Exam traps

  • Do not repeatedly aspirate a typical heart-failure transudate without treating congestion or reassessing an atypical course.
  • Do not insert a drain solely because a pleural fluid is an exudate; infection risk, symptoms, imaging and accessibility determine drainage.
  • Do not measure pleural pH in a contaminated sample or ignore the clinical picture when pH is intermediate.
  • A negative cytology does not exclude malignant pleural disease.
  • Malignant effusion management is not automatically pleurodesis: consider lung expansion, indwelling catheter, prognosis and preference.
  • Drainage procedures need ultrasound guidance and safety-netting for pneumothorax, bleeding and re-expansion complications.

Illustrations

Fluid formation and lymphatic drainage balanceDiagram of the pleural space showing normal fluid turnover between parietal capillaries and lymphatics, contrasted with the imbalance producing an effusion.PassFinals · original
Chest X-ray showing pleural effusionChest radiograph with a dense basal opacity and meniscus sign at the affected costophrenic angle.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0
Large pleural effusion and adjacent lung on imagingThoracic ultrasound showing an anechoic pleural effusion above the diaphragm with adjacent lung, illustrating why ultrasound guides safe aspiration and drain placement.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0

Key sources

  1. British Thoracic Society: BTS Guideline for Pleural Disease, 2023 (UK guideline covering undiagnosed unilateral pleural effusion, pleural infection, pleural malignancy and pleural procedures.)
  2. NHS information on pleural effusion (Current NHS explanation of pleural effusion symptoms, causes and specialist assessment.)
  3. NICE NG122: Lung cancer diagnosis and management, malignant pleural effusion (NICE recommendations and surveillance material relevant to symptomatic malignant pleural effusion, drainage and longer-term pleural intervention.)
  4. BTS Guideline for Pleural Disease: pleural infection recommendations, 2023 (UK recommendations for pleural-fluid pH risk bands, intercostal drainage, antibiotics, intrapleural therapy and specialist escalation in pleural infection.)
  5. British Thoracic Society: Pleural Disease clinical pathways and decision trees, 2023 (BTS decision tree for suspected pleural infection, including pleural pH, LDH, glucose, ultrasound and drainage decisions.)
  6. British Thoracic Society: Pleural Disease Quality Standard, May 2026 (Current BTS quality statements for adult pleural effusion, pleural infection, pleural malignancy and pleural-procedure care.)
  7. BTS Guideline for Pleural Disease: pleural malignancy recommendations, 2023 (UK recommendations for symptomatic malignant effusion, pleurodesis, indwelling pleural catheter and non-expandable lung pathways.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.