Pleural Effusion 

Definition: 
A pleural effusion is the abnormal accumulation of fluid in the pleural space (the space between the visceral and parietal pleura surrounding the lungs). 

Types of Pleural Effusion 

Transudative Effusion 
Caused by systemic factors that alter hydrostatic or oncotic pressure. 

Common causes: 
Heart failure (most common) 
Cirrhosis (hepatic hydrothorax) 
Nephrotic syndrome 

Characteristics (Light’s criteria not met for exudate): 
Protein < 0.5 (pleural fluid/serum) 
LDH < 0.6 (pleural fluid/serum) 
LDH < 2/3 of the upper limit of normal serum LDH 

Exudative Effusion 
Caused by local factors like infection, inflammation, or malignancy. 

Common causes: 
Pneumonia (parapneumonic effusion) 
Tuberculosis 
Malignancy (lung, breast, lymphoma) 
Pulmonary embolism 

Characteristics (Light’s criteria): 
Protein > 0.5 
LDH > 0.6 
LDH > 2/3 upper limit of normal serum LDH 

Other Special Types: 

Haemothorax: Blood in pleural space (trauma, malignancy) 
Chylothorax: Lymphatic fluid rich in triglycerides (thoracic duct injury) 
Empyema: Purulent fluid from infection 

Pathophysiology 

Transudate: Fluid leaks due to increased hydrostatic pressure or decreased oncotic pressure without pleural inflammation. 
Exudate: Inflammation of pleura increases capillary permeability, allowing protein-rich fluid to accumulate. 

Clinical Features 

Symptoms: 
Dyspnoea (most common) 
Pleuritic chest pain 
Dry cough 
Orthopnoea in cardiac causes 

Signs: 
Decreased breath sounds on affected side 
Dullness to percussion 
Reduced tactile fremitus 
Sometimes tracheal shift away from large effusions 

Diagnosis 

Imaging: 
Chest X-ray: Blunting of costophrenic angle, meniscus sign 
Ultrasound: Detects smaller effusions, guides thoracentesis 
CT scan: Helpful for underlying causes or complex effusions 

Thoracentesis (fluid analysis): 
Appearance: Clear, turbid, bloody, chylous, purulent 
Biochemistry: Protein, LDH, glucose, pH 
Cell count: WBCs, differential (neutrophils → infection; lymphocytes → TB/malignancy) 
Microbiology: Gram stain, culture 
Cytology: Malignancy 

Light’s Criteria (to distinguish exudate vs transudate): 
Exudate if any one of: 
Pleural fluid protein / serum protein > 0.5 
Pleural fluid LDH / serum LDH > 0.6 
Pleural fluid LDH > 2/3 upper limit of normal serum LDH 

Management 

Treat underlying cause: 
Heart failure → diuretics 
Infection → antibiotics 
Malignancy → chemotherapy, drainage 

Symptomatic relief: 
Thoracentesis (especially if large or causing dyspnoea) 
Chest tube drainage for empyema or haemothorax 

Recurrent effusions: 
Pleurodesis 
Indwelling pleural catheter
 
Key Points

Always consider systemic vs local cause. 

Right-sided effusion → more likely in CHF, liver disease; 
Left-sided → may suggest malignancy, pancreatitis. 
Fluid analysis is essential; imaging alone cannot differentiate transudate vs exudate. 
Empyema requires drainage – antibiotics alone are insufficient.