Pleural Effusion

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1- Definition & Types

2- Causes (Aetiology)

3- Pathophysiology

4- Clinical Features & Examination

5- Investigations

6- Management

7- Complications

8- Core Concepts

Definition & Types

Pleural effusion is the accumulation of excess fluid in the pleural space between the visceral and parietal pleura.

Types of Pleural Effusion (based on pleural fluid analysis):

  • Transudate: Low protein and LDH. Caused by systemic factors such as increased hydrostatic pressure or decreased oncotic pressure.

  • Exudate: High protein and LDH. Caused by local factors such as inflammation, infection, or malignancy.

Light’s Criteria (used to identify exudates):
Pleural fluid is an exudate if one or more of the following are true:

  • Pleural fluid protein/serum protein ratio > 0.5

  • Pleural fluid LDH/serum LDH ratio > 0.6

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

© image from Wikimedia Commons

Causes (Aetiology)

Transudative Effusions:

  • Congestive heart failure

  • Cirrhosis (hepatic hydrothorax)

  • Nephrotic syndrome

  • Hypoalbuminaemia

  • Peritoneal dialysis

Exudative Effusions:

  • Parapneumonic effusion (due to pneumonia)

  • Tuberculosis

  • Malignancy (especially lung and breast cancer, lymphoma)

  • Pulmonary embolism

  • Connective tissue diseases (e.g. rheumatoid arthritis, systemic lupus erythematosus)

  • Trauma

  • Post-surgical or post-radiotherapy

Pathophysiology

Pleural fluid homeostasis is maintained by a balance between production and absorption. This balance can be disrupted by:

  • Increased hydrostatic pressure (e.g. in heart failure)

  • Decreased oncotic pressure (e.g. in nephrotic syndrome, hypoalbuminaemia)

  • Increased capillary permeability (e.g. in inflammation, infection)

  • Impaired lymphatic drainage (e.g. in malignancy)

The resulting accumulation of fluid impairs lung expansion and gas exchange.

Clinical Features & Examination

  • Symptoms:

    • Progressive breathlessness

    • Pleuritic chest pain

    • Non-productive cough

    • Often asymptomatic if the effusion is small

    Signs:

    • Decreased chest expansion on the affected side

    • Stony dullness to percussion over the fluid

    • Diminished or absent breath sounds

    • Decreased tactile vocal fremitus

    • Tracheal deviation away from the affected side (in large effusions)

    • Reduced vocal resonance

© image from Wikimedia Commons

Investigations

Imaging:

  • Chest X-ray: Blunting of the costophrenic angle, fluid level, mediastinal shift if large

  • Ultrasound: Sensitive for small effusions; guides safe thoracocentesis

  • CT thorax: Useful if malignancy or complex pathology is suspected

Pleural Fluid Analysis (after thoracocentesis):

  • Appearance (clear, turbid, purulent, bloody)

  • Protein, LDH, glucose, pH

  • Cytology for malignant cells

  • Gram stain, culture, and acid-fast bacilli testing (if TB suspected)

Blood tests:

  • Serum protein and LDH (for Light’s criteria comparison)

  • Full blood count, CRP/ESR

  • Renal and liver function tests

  • Autoantibodies if connective tissue disease suspected

Management

Underlying Cause:

  • Heart failure: diuretics

  • Infection: appropriate antibiotics

  • Malignancy: oncological therapy ± pleurodesis

Symptomatic Relief:

  • Therapeutic thoracocentesis: improves breathlessness

  • Chest drain: if effusion is large, recurrent, or purulent (empyema)

  • Pleurodesis: for recurrent malignant effusion (usually talc)

Surgical options:

  • Video-assisted thoracoscopic surgery (VATS) for biopsy or decortication in empyema

Complications

  • Respiratory compromise

  • Infection leading to empyema

  • Pneumothorax (iatrogenic)

  • Fibrosis or trapped lung

  • Reaccumulation of fluid

  • Septation or loculated effusion

Core Concepts

  • Light’s criteria are essential for distinguishing transudates from exudates.

  • Bilateral effusions are more likely to be transudative; unilateral effusions should prompt diagnostic thoracocentesis.

  • Tuberculosis and malignancy are common causes of unilateral exudative effusions.

  • Always consider ultrasound guidance before pleural procedures to minimise complications.

  • Low pleural fluid glucose or pH suggests infection, malignancy, or rheumatoid effusion.

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