Pleural effusion

Etiology

• Increased influx from pleural vessels and decreased efflux via lymphatic system of pleural fluid

Differential Diagnosis

• Transudative
  • Heart failure, unless post-diuresis
  • Cirrhosis
  • Nephrotic syndrome
  • Peritoneal dialysis
  • Atelectasis
• Exudative
  • Infection, including parapneumonic effusion
  • Malignancy
  • Connective tissue disorders
  • Inflammatory disorders
  • Movement of fluid from abdomen to pleural space
  • CABG
  • Pulmonary embolism
• Medication (check Pneumotox online)
  • Methotrexate
  • Amiodarone
  • Nitrofurantoin
  • Phenytoin
  • Beta-blockers
• Asbestosis

Fluid Analysis

• Light's Criteria
  • Exudate is exudative if at least one of:
    • Pleural fluid to serum protein ratio > 0.5
    • Pleural fluid to serum lactate dehydrogenase (LD) ratio > 0.6
    • Pleural fluid LD level > 2/3 of upper limit of normal
      • ULN usually ~220, so LD > 148
• Modified Light's Criteria
  • Protein >29
  • LDH >0.45 times serum LDH
  • Pleural cholesterol >1.165 mmol/L
• Also albumin gradient and BNP can help differentiate
• pH
  • Normal: 7.60-7.64
  • Exudate: 7.30-7.45
  • Transudate: 7.40-7.55
  • <7.2
    • Malignancy
    • Empyema (low glucose)
    • TB
    • Rheumatoid arthritis (especially if really low glucose)
• Glucose <3.3
  • Malignancy
  • Empyema
  • TB
  • Rheumatoid arthritis (especially when <1.6)

Clinical Manifestations

• History of CHF, cirrhosis, CKD, TB, malignancy
• Decreased lung sounds with dullness on percussion

Investigations

• Labs
  • Pleural fluid and serum protein and LDH
• Imaging
  • CXR is first-line imaging
    • Blunting suggests at least 200mL of effusion
    • Lateral more sensitive (50mL)
    • Lateral decubitus is also helpful to rule out loculations
  • Bedside ultrasound is best for internal medicine
    • More sensitive than CXR (3-5mL)
    • Better than CT for assessing the pleura
• Thoracentesis
  • Risks
    • Pneumothorax <5%
    • Hemothorax 1%
      • Avoid if INR >3 or platelets <25
    • Re expansion pulmonary edema <1%
      • Avoid taking more than 1-2L
  • Diagnostic requires 50mL (5-10 for microbiology, 2-5 for biochemistry, 20-40 for cytology)