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Pleural Effusion

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Overview

An anatomical space is found between two structures that are normally pressed together with the potential to form a space if something were to fill the gap between them (such as fluid). The pleural space is the space between the visceral and parietal pleura of the lung and normally has a small amount of fluid within it. When excessive fluid accumulates in the pleural space, this is known as a pleural effusion.

Causes

Overview

The causes of pleural effusion can be transudates or exudates depending on their protein concentration:

  • Transudates (protein: <30 g/L):
    • Usually seen due to systemic conditions altering hydrostatic and oncotic pressures i.e. fluid is moving across one region into the pleural space (the fluid usually has a low protein content)
  • Exudates (protein: >30 g/L):
    • Usually seen when local factors are altered due to inflammation, typically increased permeability of capillaries, leading to fluid leakage into the pleural space
    • Therefore, causes are typically inflammatory

Transudative causes

Exudative causes

Presentation

Features patients may have are:

  • Dyspnoea:
    • Due to the effusion taking up space and reducing lung volume
  • Dullness to percussion on examination:
    • Due to the presence of the effusion
  • Reduced breath sounds over the area of effusion
  • Pleuritic chest pain
  • Cough
  • Features of associated conditions such as heart failure

Investigations

All patients

  • Chest x-ray:
    • Shows blunting or blurring of the costophrenic angles
    • Shows a clear fluid level
    • The trachea deviates away from the opacification
  • Thoracic ultrasound:
    • Useful for guiding thoracentesis and more specific than X-rays for detecting pleural effusions
  • CT with contrast:
    • To investigate underlying cause
  • Pleural aspiration + microscopy, culture, sensitivities, cytology, and biochemistry:
    • Done with ultrasound guidance
    • Exudates:
      • Protein level >30 g/L
    • Transudates:
      • Protein level <30 g/L
    • If the protein level is borderline (between 25-35 g/L), use Light’s criteria (see below)

Pleural Fluid Interpretation

Blood

Blood in the pleural fluid can be caused by:

Pleural pH

Reduced pleural pH (<7.20) can be caused by:

  • Infection
  • Empyema
  • Malignancy
  • Connective tissue diseases – rheumatoid arthritis and systemic lupus erythematosus
  • Tuberculosis
  • Oesophageal rupture

Pleural glucose

Reduced pleural glucose (<3.3 mmol/L) can be caused by:

  • Empyema
  • Malignancy
  • Connective tissue diseases – rheumatoid arthritis and systemic lupus erythematosus
  • Tuberculosis
  • Oesophageal rupture

Other measures

Other factors measured in pleural fluid analysis are:

  • White cell count and differential:
    • Elevated counts suggest malignancy or tuberculosis
  • Lactate dehydrogenase (LDH):
    • Used in Light’s criteria (see below)
  • Pleural fluid amylase:
    • Elevated counts suggest pancreatitis or oesophageal rupture

Diagnosis

Light’s criteria

Light’s criteria should be used if the pleural fluid protein level is between 25-35 g/L. An exudate is likely if any one of the following applies:

  • Pleural fluid divided by serum protein is >0.5
  • Pleural fluid LDH divided by serum LDH >0.6
  • Pleural fluid LDH more than 2/3s of the upper limit of normal serum LDH

Management

Pleural infection

Any patient with the following features should have a diagnostic pleural fluid aspiration for sampling followed by the insertion of a chest tube:

  • If the pleural effusion occurs in association with sepsis or pneumonia
  • If the fluid is purulent, turbid, or cloudy
  • If the fluid is clear, but the pH is <7.20 and infection is suspected

Overview

  • 1st-line: pleural aspiration:
    • This is involved in diagnosing and identifying the underlying cause of the effusion and may provide therapeutic relief, however, the effusion can often recur
  • Chest drains may be inserted which are then removed once the underlying cause has been treated
  • Other options include surgical shunts, indwelling drainage catheters, or pleurodesis (adhesion of the visceral and parietal pleura)

Complications

  • Atelectasis (lobar collapse):
    • Occurs if too much fluid is drained too quickly
  • Pneumothorax:
    • Can occur following thoracentesis and chest drain use

Prognosis

  • The prognosis depends on the underlying cause of the pleural effusion

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