Pleural Effusion: Light's Criteria, Fluid Analysis and

Year 4 · Internal Medicine · Respiratory — Based on the Pleural Effusion clinical deck, expanded with Light's criteria, BTS pleural guidance and Davidson's Medicine. Definition A pleural effusion is an abnormal accumulation of fluid in the pleural space between the visceral (lung) and parietal (chest wall) pleura. Normal Physiology 5–15 mL of lubricating serous fluid normally lies between the pleural layers. Fluid is filtered from parietal pleural capillaries and removed by parietal lymphatics . An effusion restricts lung expansion , causing symptoms. Mechanisms: Starling Forces Mechanism Effect Example --- --- --- ↑ Hydrostatic pressure Pushes fluid out Heart failure ↓ Oncotic pressure Fails to hold fluid in Hypoalbuminaemia ↑ Capillary permeability Leaky vessels Pneumonia ↓ Lymphatic drainage Blocked exit Malignancy Trans-diaphragmatic flow Fluid from abdomen Hepatic hydrothorax, pancreatitis Clinical Presentation Pleuritic chest pain — sharp on inspiration (parietal pleural inflammation) Dyspnoea — lung compression Orthopnoea and fever if infective Features of the cause — weight loss (malignancy), night sweats (TB), oedema (heart failure) Small effusions (<300 mL) may be completely asymptomatic. Physical Examination Asymmetric expansion — lagging on the affected side Stony dullness — highly characteristic Absent / reduced breath sounds Reduced tactile vocal fremitus (fluid absorbs vibration) Bronchial breathing / aegophony at the upper fluid border Massive effusion pushes the trachea away Percussion differential Condition Percussion Fremitus Breath sounds Trachea --- --- --- --- --- Pleural effusion Stony dull ↓ ↓/absent Away (massive) Consolidation Dull ↑ Bronchial Central Pneumothorax Hyper-resonant ↓ ↓/absent Away (tension) Collapse Dull ↓ ↓ Towards Imaging Chest X-ray Costophrenic angle blunting Meniscus sign — concave, homogeneous opacity ~ 200–300 mL needed on an upright PA film Supine films may only show a layering haze Ultrasound — bedside gold standard Detects as little as 20 mL Shows septations and loculated fluid Guides thoracentesis safely CT chest — the detailed investigator Finds causes: malignancy, PE, lung abscess Pleural thickening or nodularity Distinguishes empyema (split-pleura sign) from lung abscess Diagnostic Thoracentesis Indication: any new, unexplained unilateral effusion 1 cm on imaging. Safety rule: pass the needle over the top of the lower rib to avoid the intercostal vein, artery and nerve under each rib. Complications: pneumothorax, bleeding, infection, re-expansion oedema (avoid 1.5 L at once). Send: appearance, protein and LDH (with serum values), glucose, pH , cell count and differential, Gram stain, culture, AFB, GeneXpert , cytology ; optionally ADA, amylase, triglycerides, albumin, haematocrit. Transudate vs Exudate Transudate (systemic problem) Exudate (local problem) --- --- --- Appearance Clear / straw-coloured Cloudy / opaque Mechanism Pressure (hydrostatic/oncotic); capillaries intact Inflamed, leaky capillaries or blocked lymphatics Protein Low (<3 g/dL) High LDH Low High Cells Few Many Light's Criteria An effusion is EXUDATIVE if ANY ONE is met: 1. Fluid protein / serum protein 0.5 2. Fluid LDH / serum LDH 0.6 3. Fluid LDH ⅔ upper limit of normal serum LDH Exam pearl: all negative = transudate. Only one positive proves an exudate. Exam trap: diuretics in heart failure Diuretics remove water from the pleural space but leave protein behind. A true transudate becomes concentrated and falsely meets Light's criteria . Solution: serum–pleural albumin gradient 1.2 g/dL proves a transudate. Causes Transudates Congestive heart failure — commonest cause of bilateral effusions; ↑ hydrostatic pressure Cirrhosis (hepatic hydrothorax) — ascites crosses diaphragmatic defects; usually right-sided Nephrotic syndrome — urinary protein loss → ↓ oncotic pressure Severe hypoalbuminaemia Others: hypothyroidism, peritoneal dialysis, Meigs' syndrome Exudates Infection: parapneumonic effusion / empyema, tuberculosis (common in Kenya, especially with HIV) Malignancy: lung, breast, lymphoma, mesothelioma — about 25% of effusions Pulmonary embolism: ~ 80% exudative , 20% transudative Autoimmune / inflammatory: rheumatoid arthritis, SLE, pancreatitis, oesophageal rupture Special Fluid Analysis Appearance Think of Confirm --- --- --- Bloody Malignancy, trauma, PE Haemothorax if fluid haematocrit 50% of blood Milky Chylothorax — thoracic duct disruption (lymphoma, trauma) Triglycerides 110 mg/dL Purulent Empyema Needs immediate chest drain Pseudochylothorax (chronic TB/RA) has high cholesterol and crystals, not triglycerides. The pH clue: parapneumonic effusions Type Features Management --- --- --- Simple Sterile, free-flowing, pH 7.20 Antibiotics Complicated Bacterial invasion, pH < 7.20 , high LDH, often loculated Chest drain Empyema Frank pus / positive Gram stain Chest drain ± surgery Low glucose (< 60 mg/dL) — mnemonic MEAT M — Malignancy E — Empyema A — Arthritis (rheumatoid — often <