Pleural effusion

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  • 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



  • 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
  • US



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


See Also

External Links