Pleural effusion


Lobes of the lung with related anatomy.
  • Exudative
    • Active fluid secretion or leakage with high protein content
  • Transudative
    • Imbalance between hydrostatic (e.g. CHF) and oncotic (e.g. nephrotic syndrome)
    • Fluid has low protein content

Clinical Features

  • SOB
  • Decreased breath sounds
  • Frequently found on CXR

Differential Diagnosis

Pleural effusion.png


  • Transudative
  • Exudative
    • Cancer
    • Pneumonia (parapneumonic effusion)
      • Occurs in 40% of patients hospitalized with pneumonia
    • PE
      • Occurs in 30% of patients with PE

Less Common

Non-infectious Effusions


Pleural effusion on CXR (right).
A massive left pleural effusion displacing the heart and trachea to the right.
A pleural effusion: as seen on chest X-ray. The A arrow indicates fluid layering in the right chest. The B arrow indicates the width of the right lung. The volume of the lung is reduced because of the collection of fluid around the lung.
CT scan of the chest showing right-sided pleural effusion.
Pleural effusion on ultrasound.


  • CXR
    • Earliest sign is blunting of costophrenic angle
    • Lateral decubitus with affected side down requires 50-75 cc of fluid for visualization
      • PA view requires 200-250 cc of fluid
      • Supine view may only show a generalized hazy appearance of affected hemithorax
    • Subpulmonic effusion
      • Fluid collects in isolation between lung base and diaphragm
      • May not cause blunting of costophrnic angle or meniscus appearance
      • Suspect if "hemidiaphragm" (actually fluid) is elevated and flattened
      • Lateral decubitus with suspected side down will show free-flowing pleural fluid
  • CT
  • Lung ultrasound
  • Thoracentesis


Exudative versus Transudative (Light's Criteria)

  • If one of the following is present the fluid is virtually always an exudate
  • If none is present the fluid is virtually always a transudate
    • Pleural fluid/serum protein ratio >0.5
    • Pleural fluid/serum LDH ratio >0.6
    • Pleural fluid LDH > two thirds of upper limit for serum LDH

Exudative Work-up

  • Gram stain and culture (place 10cc into blood culture bottle at the bedside)
  • Cell count
    • RBC >100K: trauma, malignancy, pneumonia, or pulmonary infarction
    • Neutrophil predominance (>50%): parapneumonic, pulmonary embolism, pancreatitis
    • Lymphocytic predominance (>50%): malignancy, TB, PE, viral pleuritis
  • Glucose
    • Low glucose (<60) seen in parapneumonic, empyema, malignant, TB, and RA
  • ABG (pH)
    • May be left at room temperature for up to 1hr with out affecting results
    • Normal pleural fluid pH = 7.64;
    • In parapneumonic effusions, <7.10 predicts development of empyema or persistence and indicates need for thoracostomy tube drainage
  • Amylase: >100 in pleural effusions due to pancreatitis or esophageal rupture
  • TB (adenosine deaminase)
  • India ink
  • Cytology (requires 50cc)


  • Dyspnea at rest:
    • Therapeutic thoracentesis with max drainage 1-1.5L to avoid reexpansion pulmonary edema
  • Patient positioning (lateral decubitus) for unilateral pleural effusions
    • Most of the time, "Good lung to Ground" to improve V/Q mismatch
    • Exceptions in which "bad" lung should be "down":
      • Massive hemoptysis
      • Severe/large pleural effusions
      • Large pulmonary abscesses
  • Empyema
    • Drain with large-bore thoracostomy tube
  • Parapneumonic Effusion:
    • Consider thoracostomy tube drainage if:
      • Comorbid disease
      • Aspiration of frank pus (empyema)
      • Failure to respond to antibiotic treatment
      • Anaerobic organisms
      • Pleural fluid pH <7.20
      • Pleural fluid glucose < 60 mg/dl
      • Effusion involving >50% of thorax or air-fluid level on CXR
      • Loculated effusion
  • CHF
    • Diuretic therapy resolves >75% of effusions within 2-3d


  • All new pleural effusions of non-trace size typically require admission

See Also

External Links