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).

🎯 EXAM ANCHOR – CORE CONCEPT 

  • Pleural effusion = fluid accumulation in the pleural space

  • Classified as transudate or exudate

  • Cause determines management

📌 PARA commonly asks:

What is a pleural effusion?

🔬 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

🎯 EXAM ANCHOR – COMMON CAUSES (PARA)

  • Heart failure = most common cause overall

  • Malignancy = common cause of unilateral exudative effusion

  • Parapneumonic effusion common with infection

📌 PARA commonly asks:

What is the most common cause of pleural effusion?

📋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

🎯 EXAM ANCHOR – CLINICAL SIGNS

  • Reduced breath sounds

  • Stony dull percussion

  • Reduced chest expansion

  • Egophony above effusion

📌 PARA commonly asks:

What percussion note is expected in pleural effusion?

🔍 Investigations

🧠 Mnemonic: PLEURA

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

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

🎯 EXAM ANCHOR – IMAGING (PARA)

  • CXR shows blunted costophrenic angle

  • Ultrasound is best to confirm and guide aspiration

  • Small effusions may be missed on erect CXR

📌 PARA commonly asks:

What is the best investigation to confirm and guide pleural aspiration?

  • 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)

🎯 EXAM ANCHOR – PLEURAL FLUID ANALYSIS 

  • Send for protein, LDH, pH, cytology, culture

  • Low pH suggests infection or malignancy

  • Cytology may detect malignancy

📌 PARA commonly asks:

Which tests should pleural fluid be sent for?

 

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.

🎯 EXAM ANCHOR – TRANSUDATE vs EXUDATE 

  • Transudate: systemic cause (e.g. heart failure)

  • Exudate: local pathology (e.g. malignancy, infection, TB)

  • Differentiated using Light’s criteria

📌 PARA commonly asks:

Which investigation differentiates transudative from exudative pleural effusions?

🧾 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

🎯 EXAM ANCHOR – EMPYEMA 

  • Empyema = infected pleural fluid

  • Requires intercostal chest drain

  • Repeated aspiration alone is insufficient

📌 PARA commonly asks:

What is the definitive management of empyema?

  • Follow-up imaging

  • Long-term drain or pleurodesis if malignant

  • Ultrasound to guide any further drainage

  • Investigate recurrent effusions

  • Discuss with respiratory if unclear

🎯 EXAM ANCHOR – ASPIRATION INDICATION 

  • New unilateral pleural effusion should be aspirated

  • Exception: clear bilateral transudate responding to diuretics

  • Send fluid for full analysis

📌 PARA commonly asks:

When should a pleural effusion be aspirated?

⚠️ 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

🎯 EXAM ANCHOR – RECURRENT EFFUSION (PARA)

  • Think malignancy or TB

  • May require pleurodesis or indwelling drain

  • MDT input required

📌 PARA commonly asks:

What should be suspected in recurrent pleural effusions?

🔎 Key PARA Exam Traps

💡 Dullness to percussion + reduced breath sounds = pleural effusion (not consolidation)

💡 CXR shows blunted costophrenic angles: Small effusions may be missed on erect CXR 

💡 Ultrasound is the best test to confirm and guide aspiration

💡 Always aspirate a new unilateral pleural effusion: Unless clear cause (e.g. heart failure responding to diuretics)

💡 Light’s criteria differentiate transudate vs exudate: Exudate → malignancy, infection, PE, TB

💡 Heart failure causes bilateral transudative effusions: Asymmetrical or unilateral → think alternative cause

💡 Malignancy = common cause of unilateral exudative effusion

💡 Pleural effusion with fever and raised CRP → consider parapneumonic effusion or empyema

💡 Empyema requires chest drain: Repeated  aspiration alone is insufficient

💡 Pleural effusion can mask underlying lung cancer: Always investigate the cause, not just drain

🔎 Last updated in line with NICE NG12 (2021) + BTS Guidelines (2023)

  • PARA-aligned, reviewed February 2026


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