7. Pleural Effusion

📄 Definition

A pleural effusion is the abnormal accumulation of fluid within the pleural space. It may be transudative (e.g. heart failure) or exudative (e.g. malignancy, infection).

🔬 Pathophysiology

🧠 Mnemonic: FLUID

  • Filtration imbalance (↑hydrostatic or ↓oncotic pressure → transudate)

  • Leaky pleura (↑permeability due to inflammation → exudate)

  • Unresolved infection or malignancy

  • Impaired lymphatic drainage

  • Disruption of pleural membrane or vessels

📋 Causes

🧠 Mnemonic: HEART PLUMP
Transudates:

  • Heart failure (most common)

  • End-stage renal disease (nephrotic syndrome)

  • Albumin low (cirrhosis, malnutrition)

  • Renal failure (fluid overload)

  • Thyroid (myxoedema)

Exudates:

  • Pneumonia (parapneumonic effusion)

  • Lung cancer

  • Unknown malignancy

  • Mesothelioma

  • Pulmonary embolism

📋Clinical Features

🧠 Mnemonic: SOB CHEST

  • Shortness of breath (especially on exertion)

  • Orthopnoea (if large effusion)

  • Breath sounds reduced

  • Chest pain (pleuritic)

  • Heavy feeling on affected side

  • Egophony above the fluid

  • Stony dull percussion

  • Trickling cough (dry, irritating)

🩺 Physical Examination Findings

  • Cachexia, pallor, lymphadenopathy

  • Finger clubbing

  • Crackles/bronchial breathing

  • Spinal tenderness (if Pott’s disease)

  • Signs of effusion or consolidation

🔍 Investigations

🧠 Mnemonic: PLEURA

  • PA & lateral CXR – blunting of costophrenic angle ± meniscus sign

  • Lung ultrasound – bedside confirmation (gold standard for guiding tap)

  • Echo – rule out cardiac cause if transudate

  • Urgent aspiration if new unilateral effusion

  • Remember Light’s Criteria to differentiate

  • Analysis of pleural fluid:

    • Protein

    • LDH

    • pH

    • Cytology

    • Gram stain & culture

    • Acid-fast bacilli (TB)

Light’s Criteria Table – Differentiate Exudate vs Transudate

Test ParameterExudate if ANY of the following is true:
Pleural fluid protein / Serum protein> 0.5
Pleural fluid LDH / Serum LDH> 0.6
Pleural fluid LDH> ⅔ of upper limit of normal (ULN) serum LDH

🔑 If any of these criteria are met → it’s an exudate.

🧾 Management

🧠 Mnemonic: DRAIN FLUID

  • Determine underlying cause

  • Radiology-guided thoracentesis if diagnostic

  • Antibiotics if parapneumonic

  • Intercostal drain if empyema / large infected

  • NSAIDs for pleuritic pain

  • Follow-up imaging

  • Long-term drain or pleurodesis if malignant

  • Ultrasound to guide any further drainage

  • Investigate recurrent effusions

  • Discuss with respiratory if unclear

⚠️ Complications

  • Empyema

  • Fibrosis/trapped lung

  • Sepsis

  • Pneumothorax (iatrogenic)

  • Re-expansion pulmonary oedema (rare but fatal)

🧐 Differentials

🧠 Mnemonic: POT HAIL

  • Pneumonia

  • Oedema (cardiogenic)

  • TB

  • Haemothorax

  • Asbestos exposure (mesothelioma)

  • Infarction (PE)

  • Lung malignancy

📌 PARA Revision Tips

  • Always confirm diagnosis and safety of aspiration with USS

  • Light’s Criteria is essential exam knowledge

  • Pleural tap = send for protein, LDH, pH, cytology, culture

  • Recurrent = think malignancy or TB

  • Consider chest drain if >1/2 hemithorax or infected

🔎 Last updated in line with NICE NG12 (2021) + BTS Guidelines (2023)
Last reviewed: July 2025
🔒 PASSMAP ensures all content is NICE-aligned and reviewed for Physician Associate Registration Assessment (PARA) success.

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