Teaching Points

• Parapneumonic effusions are effusions associated with pneumonia, which can occur in about 20-25%
• If <10mm on lateral film and/or decreasing with antibiotic treatment, may continue to monitor and just treat with antibiotics.
• Lights Criteria  – differentiates transudative and exudative fluid.
  • Criteria
    • Pleural TP/Serum TP >0.5
    • Pleural LD/Serum LD >0.6
    • Pleural LD > 2/3 ULN plasma LD
  • Need at least one positive result to categorize pleural fluid as exudative.
    • Setup of Light’s criteria leads to increased sensitivity and decreased specificity.
    • Purpose is due to the fact that you don’t want to miss a process causing an exudative fluid so you want your rate of false negatives to be low. Hence an increased sensitivity.
• Cell count
  • Predominant neutrophlic – bacterial
  • Predominant lymphocytic – think TB or malignancy
  • Predominant eosinophil – think irritation due to blood, air, etc
• Complicated parapneumonic effusion associated with worse outcomes, necessitates need for drainage.
  • pH<7.2 (normal pleural fluid pH 7.6)
  • Pleural glucose <60