Pleural Effusions

Diagnosis and Classification

• The European Respiratory Society and American College of Radiology recommend using Light's criteria to classify pleural effusions as transudates or exudates, which includes protein and LDH levels in pleural fluid and serum, with the following characteristics:

  Criterion	Transudate	Exudate
  Protein fluid-to-serum ratio	≤ 0.5	> 0.5
  LDH fluid-to-serum ratio	≤ 0.6	> 0.6
  LDH in pleural fluid	≤ 2/3 upper limit of normal serum LDH	> 2/3 upper limit of normal serum LDH

  1, 2, 3

• A serum-pleural fluid albumin gradient > 1.2 g/dL suggests a transudate, but alternative criteria, such as pleural fluid LDH > 67% of upper limit of normal combined with pleural fluid cholesterol > 55 mg/dL, can be used when serum samples are unavailable 2, 3
• The European Society of Cardiology suggests that an NT-proBNP level (pleural fluid or serum) > 1500 μg/mL strongly indicates heart failure as the cause of the effusion, and clinical scoring models can aid in identification when effusions meet Light's criteria for exudates but clinical suspicion suggests heart failure 3

Management of Exudative Effusions

• The British Thoracic Society and American Thoracic Society guidelines recommend that management of exudative pleural effusions should be targeted at the underlying cause rather than using diuretics, with treatment options including corticosteroids for inflammatory causes and discontinuation of offending medications 4, 5, 2
• Malignancy, particularly adenocarcinoma and mesothelioma, is a common cause of exudative effusion, with high lactate dehydrogenase (LDH) levels and positive pleural fluid cytology in approximately 60% of cases, and the American Thoracic Society recommends drainage for symptom relief, possible pleurodesis or indwelling pleural catheter for malignant effusions 4, 5
• Pleural infection, such as empyema and complicated parapneumonic effusions, is associated with high LDH levels, low glucose, and low pH, with a high risk of mortality if left untreated, and the British Thoracic Society recommends appropriate antibiotics and drainage, with empiric antibiotics covering both aerobic and anaerobic organisms started immediately, and adjustment based on culture results 4, 2, 6
• Immediate chest tube drainage is indicated if: frankly purulent or turbid/cloudy fluid, organisms identified by Gram stain or culture, pleural fluid pH < 7.2, or loculated effusion, according to the British Thoracic Society 6

Management of Transudative Effusions

• For patients with heart failure-related refractory transudative effusions, the European Respiratory Society recommends considering pleurodesis in select cases, in addition to ultrasound-guided thoracentesis for symptomatic relief and indwelling pleural catheters (IPCs) for recurrent effusions 3
• The European Respiratory Society recommends using ultrasound guidance for all pleural procedures to reduce complications 3

Follow-up and Prognosis

• Follow-up imaging is important to ensure resolution and exclude underlying pathology, particularly for exudative effusions, as recommended by the British Thoracic Society 4
• Delaying drainage of infected or malignant effusions can lead to loculation, trapped lung, or worsening clinical status, according to the British Thoracic Society 2
• The prognosis for patients with exudative pleural effusions depends on the underlying cause, with a median survival of 3-12 months for patients with malignant pleural effusion, and a 1-year mortality rate of 46% for patients with end-stage renal disease who develop pleural effusion, as reported by the American Thoracic Society and the European Respiratory Society 7, 3, 8
• Pleural fluid pH < 7.3 is associated with worse survival, with a median of 2.1 months vs 9.8 months for pH > 7.3, according to the European Respiratory Society 4

Recurrent Effusions

• Management options for recurrent effusions include therapeutic thoracentesis, chest tube and talc slurry, thoracoscopy with talc poudrage, or indwelling pleural catheter (IPC), as recommended by the American Thoracic Society 2
• The American Thoracic Society recommends indwelling pleural catheter or chemical pleurodesis for malignant effusions 5
• The European Heart Journal recommends anti-TB treatment for 6 months for tuberculous effusions 9