Pleural effusion

Pathophysiology

Pleural fluid accumulates when there is an imbalance between fluid formation (e.g., increased hydrostatic pressure, increased permeability) and fluid absorption (e.g., decreased oncotic pressure, obstructed lymphatic drainage). Causes range from heart failure to infections, malignancies, and inflammatory conditions.

Classification: transudate vs exudate

• Light’s criteria are most commonly used to distinguish transudates from exudates.

• A pleural effusion is considered exudative if any of the following apply:

  • Pleural fluid protein/serum protein ratio > 0.5

  • Pleural fluid LDH/serum LDH ratio > 0.6

  • Pleural fluid LDH > two-thirds the upper limit of normal serum LDH

• If none of these criteria are met, the fluid is transudative.

Common causes of transudates

• Congestive cardiac failure (CCF) – up to 90% of transudative effusions

• Nephrotic syndrome

• Liver cirrhosis (often linked to hypoalbuminaemia)

• Peritoneal dialysis

Common causes of exudates

• Infection (e.g., bacterial pneumonia, tuberculosis)

• Malignancy (e.g., lung cancer, breast cancer, mesothelioma)

• Pulmonary embolism (sometimes exudative)

• Pancreatitis

• Inflammatory diseases (e.g., rheumatoid pleurisy, lupus pleuritis)

Clinical presentation

• Symptoms and signs:

  • Dyspnoea (especially if effusion > ~500 mL)

  • Pleuritic chest pain

  • Dry, non-productive cough

  • Decreased/absent breath sounds

  • Dullness to percussion

  • Reduced tactile vocal fremitus

• Severity generally correlates with the volume of pleural fluid and/or rate of accumulation.

Red flags

• Rapidly accumulating fluid

• Systemic symptoms (e.g., fevers, night sweats, weight loss)

• Suspicion of empyema or haemothorax

Investigations

• Imaging:

  • Chest X-ray: blunting of the costophrenic angle; consider lateral decubitus view if needed

  • Ultrasound: high sensitivity for detecting fluid; guides diagnostic aspiration

  • CT chest: characterises underlying lung pathology; detects complex effusions

• Diagnostic thoracentesis (pleural aspiration):

  • Recommended for new, unexplained moderate or large effusions

  • Performed under direct ultrasound guidance (reduces risk of pneumothorax)

  • Pleural fluid analysis:

    • Biochemical tests: protein, LDH, pH, glucose

    • Appearance: cloudy, bloody, purulent

    • Cytology: check for malignant cells

    • Microbiology: culture (including TB if suspected)

  • If tuberculosis or malignancy is strongly suspected, consider pleural biopsy in addition to fluid aspiration.

Management overview

• Treat the underlying cause; management differs for transudates vs exudates.

• Transudative effusions: address underlying systemic disease (e.g., optimise heart failure therapy, manage cirrhosis, control nephrotic syndrome).

• Exudative effusions: investigate for infection or malignancy; may require antibiotics, drainage, chemotherapy, pleurodesis, etc.

Specific scenarios

Parapneumonic effusions and empyema

• A parapneumonic effusion occurs as a complication of pneumonia and can progress to empyema (frank pus or positive pleural fluid cultures) if not managed appropriately.

• Drainage is indicated for:

  • Large effusions (> one-third of the hemithorax)

  • Persistent fever/systemic signs of infection despite adequate antibiotics

  • Loculated effusions (seen on ultrasound or CT)

  • Frankly purulent fluid

  • Pleural fluid pH < 7.2 or LDH > 1,000 U/L

• Empyema always requires drainage (e.g., with an intercostal tube).

• Intrapleural enzyme therapy: combination of alteplase (tPA) and dornase alfa can help fluid drainage (not TGA-registered for this indication, but recommended by guidelines).

• Antibiotics are guided by culture results and local protocols.

Malignant pleural effusion

• Often associated with a poor prognosis, particularly if recurrent.

• Key focus on symptomatic relief:

  • Therapeutic thoracentesis for drainage

  • Reaccumulation is common

• Strategies to prevent or reduce recurrent fluid:

  • Pleurodesis (talc slurry/poudrage)

  • Indwelling tunnelled pleural catheter (especially if lung is trapped or per patient preference)

• Management usually involves a multidisciplinary team (respiratory physicians, oncologists, palliative care).

Heart failure and other transudative causes

• Congestive cardiac failure: diuretics, fluid restriction, and optimal medication regimens (ACE inhibitors, beta-blockers, etc.).

• Nephrotic syndrome: address proteinuria and the underlying renal disease.

• Cirrhosis: sodium restriction, diuretics (spironolactone ± loop diuretic), possibly paracentesis if significant ascites.

• Mild, asymptomatic effusions: can be monitored closely.

Pleurodesis

• Indicated for recurrent effusions causing morbidity or reduced quality of life.

• Talc pleurodesis is commonly performed, particularly for malignant effusions.

• Adequate analgesia is necessary to facilitate this procedure.