Pleural Effusion

Overview

The normal pleural space contains 10–20 mL of fluid. Chest X-ray can detect an effusion from around 300 mL; clinical signs (decreased breath sounds, dullness to percussion) typically appear from around 500 mL. Shortness of breath occurs with large effusions; pleuritic chest pain suggests infection or trauma.

Effusions are classified as transudative or exudative (Light’s criteria).

Transudative effusions

Protein <25 g/L, LDH <200 IU/L. Most transudates occur for clinically obvious reasons and don’t necessarily need diagnostic sampling.

Causes: heart failure (~90% of transudates), hypoproteinaemia (e.g. nephrotic syndrome), ascites, constrictive pericarditis, hypothyroidism, Meigs syndrome (ovarian tumour → right-sided effusion + ascites).

Exudative effusions

Protein >35 g/L, LDH >200 IU/L.

Causes: infection (parapneumonic — may progress to empyema; TB; viral), malignancy (mesothelioma, bronchial carcinoma, metastases), pulmonary infarction, connective tissue disease, pancreatitis, lymphoma, sarcoidosis, HIV with parasitic pneumonia.

Parapneumonic effusion and empyema

Complicates up to 50% of pneumonia cases. Starts sterile but may progress to a collection of pus (empyema). A clinically significant parapneumonic effusion should be sampled and cultured. Empyema always requires drainage.

Indications for drainage of a parapneumonic effusion:

• Not responding to appropriate antibiotic therapy (e.g. ongoing fevers/sepsis)
• Large size (>1/3 of the hemithorax)
• Loculated effusion
• Evidence of fluid infection: purulent fluid on sampling, organisms on culture/Gram stain, fluid pH <7.2, or LDH >1000 IU/L

Drainage is via chest tube insertion; VATS may be needed if simple drainage fails (e.g. for loculated collections).

Malignant pleural effusions

Presence of a malignant effusion is an adverse prognostic factor. Re-accumulation after drainage is common.