Parapneumonic Effusion 

1. Definition

Parapneumonic effusion refers to pleural fluid accumulation associated with pneumonia, lung abscess, or bronchiectasis.

It represents a spectrum of pleural infection, ranging from sterile exudative fluid to frank pus in the pleural space.

👉 Important Clinical Concept
Not all parapneumonic effusions are infected initially, but untreated effusions may progress to empyema.

2. Epidemiology and Clinical Importance

• Occurs in 20–40% of hospitalized pneumonia patients
• Empyema develops in 5–10%
• Mortality increases significantly if drainage is delayed
• Common ICU complication in severe pneumonia

High-risk populations:

• Elderly
• Diabetes
• Alcoholism
• Immunosuppression
• Aspiration pneumonia
• Prolonged mechanical ventilation

3. Pathophysiology

Pleural infection evolves through three classical stages.

Stage 1 — Exudative Phase (Simple Parapneumonic Effusion)

Mechanism

• Increased vascular permeability
• Sterile inflammatory fluid enters pleural space

Pleural Fluid Characteristics

• Sterile
• Free flowing
• Low cellularity
• Normal glucose
• Normal pH (>7.2)

Clinical Importance

👉 Usually resolves with antibiotics alone

Stage 2 — Fibrinopurulent Phase (Complicated Effusion)

Mechanism

• Bacterial invasion of pleural space
• Neutrophil activation
• Fibrin deposition
• Septation and loculation formation

Pleural Fluid Changes

• ↓ pH (<7.2)
• ↓ glucose (<60 mg/dL)
• ↑ LDH
• Positive culture sometimes

👉 Requires drainage + antibiotics

Stage 3 — Organizing Phase (Empyema)

Mechanism

• Fibroblast proliferation
• Thick pleural peel formation
• Lung entrapment

👉 Requires surgical intervention often

4. Microbiology

Depends on pneumonia type.

Community-Acquired Pneumonia

• Streptococcus pneumoniae
• Streptococcus anginosus group
• Staphylococcus aureus
• Anaerobes (aspiration)

Hospital-Acquired Pneumonia

• MRSA
• Pseudomonas aeruginosa
• Gram-negative bacilli

Special Situations

• Tuberculosis
• Fungal infections
• Polymicrobial aspiration infections

5. Clinical Features

Symptoms often overlap with pneumonia.

Symptoms

• Fever
• Pleuritic chest pain
• Dyspnea
• Persistent cough
• Failure to improve with antibiotics

Signs

• Reduced chest expansion
• Stony dull percussion
• Reduced breath sounds
• Pleural rub early

6. Radiological Evaluation

• Blunting of costophrenic angle
• Homogeneous opacity
• Meniscus sign
• Large effusions cause mediastinal shift

👉 Lateral decubitus film helps detect small effusions

Ultrasound – ICU Gold Standard

CT Findings

• Split pleura sign
• Pleural thickening
• Loculations
• Lung entrapment

👉 Useful when:

• Drainage fails
• Surgery planning
• Diagnostic uncertainty

7. Diagnostic Thoracentesis

Parapneumonic effusions are always exudative.

Key Parameters Determining Drainage Need

8. Classification (American College of Chest Physicians – Risk Stratification)

Category 1 – Very Low Risk

• Small effusion
• Free flowing
• No thoracentesis needed

Category 2 – Low Risk

• Small/moderate
• Negative culture
• pH > 7.2

👉 Antibiotics only

Category 3 – Moderate Risk

• Loculated effusion
• pH < 7.2
• Glucose < 60

👉 Chest tube drainage needed

Category 4 – High Risk

• Empyema (pus)
• Positive culture

👉 Mandatory drainage ± surgery

9. Management

A. Antibiotic Therapy

Start Early – Do Not Delay Drainage

Community-Acquired

• Ceftriaxone + Azithromycin
  OR
• Ampicillin-sulbactam
  OR
• Piperacillin-tazobactam (severe)

Aspiration

• Add anaerobic coverage
• Metronidazole or beta-lactam/beta-lactamase inhibitor

Hospital-Acquired

• Anti-pseudomonal + MRSA coverage
• Piperacillin-tazobactam / Meropenem
• Add Vancomycin or Linezolid

Duration

• 2–6 weeks depending on severity

B. Pleural Drainage

1. Therapeutic Thoracentesis

• For small free flowing effusions
• Diagnostic + therapeutic

2. Chest Tube (Tube Thoracostomy)

Indications:

• Empyema
• pH <7.2
• Positive Gram stain
• Loculated effusion

Preferred:

• Small bore catheters (10–14 Fr) equally effective

3. Intrapleural Fibrinolytics

Drugs

• tPA + DNase

Evidence

MIST-2 trial:

• Improves drainage
• Reduces surgery need

4. Surgical Management

Indications

• Failed drainage
• Organized empyema
• Lung trapped by pleural peel

Options

• VATS decortication
• Open thoracotomy