What is spontaneous parapneumonic pleural effusion?

Spontaneous Parapneumonic Pleural Effusion

A spontaneous parapneumonic pleural effusion is a collection of fluid in the pleural space that develops in association with an underlying pneumonia, representing the exudative stage in the continuum of pleural infection. 1 These effusions occur in approximately 40% of patients with pneumonia and can range from simple, uncomplicated collections that resolve with antibiotic therapy alone to complicated effusions requiring drainage interventions 2.

Classification and Staging

Parapneumonic effusions follow a progressive continuum that can be divided into three distinct stages:

1. Exudative Stage (Simple Parapneumonic Effusion)

   • Clear fluid accumulates in the pleural space
   • Low white cell count
   • Inflammatory response to adjacent pneumonia
   • Usually resolves with antibiotic therapy alone 1

2. Fibropurulent Stage (Complicated Parapneumonic Effusion)

   • Fibrin deposition in the pleural space
   • Formation of septations and loculations
   • Increased white cell count
   • Fluid thickens and may become purulent
   • Often requires drainage 1

3. Organizational Stage

   • Fibroblast infiltration of the pleural cavity
   • Development of thick, non-elastic pleural "peel"
   • May prevent lung re-expansion ("trapped lung")
   • Can impair lung function
   • May require surgical intervention 1

Epidemiology

• Parapneumonic effusions account for approximately one-third of all pleural effusions 2
• Occur in about 40% of patients with pneumonia 2, 3
• Associated with increased morbidity and mortality 2
• Incidence has been increasing in recent years 4, 5
• More common in autumn and winter months 5

Pathophysiology

Parapneumonic effusions develop when:

• Inflammation from pneumonia extends to the pleural surface
• An imbalance occurs between pleural fluid formation and drainage
• Normal pleural fluid contains few cells (mesothelial cells, macrophages, lymphocytes) with low protein concentration
• During infection, inflammatory exudates develop with predominant polymorphonuclear leukocytes 1
• Progressive biochemical changes include decreasing pH and glucose levels with increasing LDH levels 1

Clinical Presentation

Patients with parapneumonic effusions may present with:

• Prolonged fever despite appropriate antibiotic therapy
• Respiratory distress (present in 60% of cases) 5
• Chest pain (present in 39% of cases) 5
• Physical examination findings may include:
  • Dullness to percussion
  • Diminished breath sounds
  • Changes in quality of transmitted breath sounds and speech 1

Diagnosis

Diagnosis of parapneumonic effusions involves:

1. Imaging

   • Chest radiography (including lateral decubitus views) is the initial test to confirm pleural fluid 1
   • If radiography is inconclusive, chest ultrasound or CT is recommended 1
   • Ultrasound can identify loculations and septations 1

2. Thoracentesis

   • Essential for distinguishing between complicated and uncomplicated effusions 4
   • Pleural fluid analysis should include:
     • Visual appearance (clear vs. turbid/purulent)
     • pH (critical value: <7.2 indicates need for drainage) 1
     • Glucose level
     • LDH level
     • Protein content
     • Cell count and differential
     • Gram stain and culture 3

Management

Management depends on the stage and characteristics of the effusion:

1. Simple Parapneumonic Effusions

   • Antibiotics alone if:
     • Small effusion (<10mm on ultrasound)
     • pH >7.2
     • No organisms on Gram stain or culture
     • Good clinical progress 1

2. Complicated Parapneumonic Effusions

   • Require drainage if:
     • Frankly purulent or turbid/cloudy fluid
     • Organisms identified on Gram stain or culture
     • pH <7.2
     • Poor clinical progress on antibiotics alone 1
     • Loculated effusion 5

3. Drainage Options

   • Therapeutic thoracentesis for smaller effusions
   • Chest tube drainage for larger, free-flowing effusions
   • Video-assisted thoracoscopic surgery (VATS) for loculated effusions or empyema 3

Prognostic Factors

Factors associated with worse prognosis include:

• Respiratory distress
• Presence of loculations
• Empyema
• Low pH in pleural fluid
• Low glucose in pleural fluid
• High LDH level in pleural fluid
• High serum C-reactive protein 5

Common Pitfalls

1. Delayed diagnosis and intervention

   • Tube drainage becomes increasingly difficult the longer it is delayed 6
   • Monitor patients with pneumonia closely for development of effusions

2. Inadequate sampling

   • Small effusions may be difficult to sample
   • Use ultrasound guidance for difficult thoracentesis 1

3. Misinterpreting pleural fluid analysis

   • Remember that absolute protein values are not useful for determining drainage requirements 1
   • pH is the most reliable indicator for need of drainage 1

4. Inappropriate antibiotic selection

   • Microbial epidemiology of pleural infections differs from pneumonia
   • Higher prevalence of anaerobic bacteria in pleural infections 4
   • Antibiotics should be active against anaerobic bacteria except in pneumococcal infections 4