Empyema Thoracis

1. Etiology

Empyema is usually a complication of bacterial pneumonia (parapneumonic effusion).

• Common Organisms:
  • Streptococcus pneumoniae: Currently the most common cause (even in vaccinated populations due to serotype replacement).
  • Staphylococcus aureus: Significant cause, especially in infants and developing nations; associated with pneumatoceles.
  • Streptococcus pyogenes (Group A Strep).
• Other Causes:
  • Anaerobes: Secondary to aspiration pneumonia or poor dental hygiene.
  • Mycobacterium tuberculosis: Chronic effusions.
  • Haemophilus influenzae type b: Rare in vaccinated children.
  • Mycoplasma pneumoniae: Can cause effusions, though frank empyema is rare.

2. Stages of Evolution

Pleural infection progresses through a continuum of three distinct stages:

1. Exudative Stage (Simple Parapneumonic Effusion):

   • Pathology: Inflammation increases pleural membrane permeability.
   • Fluid: Clear, sterile exudate, low WBC count, normal pH (>7.2), normal glucose.
   • Mechanics: Fluid flows freely; lungs expand easily.

2. Fibropurulent Stage (Complicated Parapneumonic Effusion):

   • Pathology: Bacterial invasion of pleural space, neutrophil accumulation, and fibrin deposition.
   • Fluid: Turbid/purulent (pus), high WBC (polymorphs), low pH (<7.2), low glucose, high LDH.
   • Mechanics: Fibrin strands create loculations and septations; lung expansion is limited.

3. Organizational Stage (Chronic Empyema):

   • Pathology: Fibroblast infiltration leads to formation of a thick, non-elastic "peel" over the visceral and parietal pleura.
   • Mechanics: The peel encases the lung causing "trapped lung", preventing re-expansion and impairing function.

3. Clinical Manifestations

• History:
  • Persistence or recurrence of fever in a child treated for pneumonia (>48 hours after admission).
  • Symptoms: Pleuritic chest pain (may be referred to abdomen), dyspnea, malaise, anorexia.
• Physical Examination:
  • General: Respiratory distress, toxic look, pallor.
  • Chest Signs: Unilateral reduction in chest expansion, stony dullness on percussion, decreased or absent breath sounds on the affected side.
  • Scoliosis: Transient scoliosis (concave to the affected side) due to pain/splinting.

4. Diagnostic Investigations

A. Imaging

• Chest X-ray (CXR): Initial test. Shows blunting of costophrenic angle, meniscus sign, or "white out". Cannot differentiate simple fluid from pus.
• Ultrasound Chest (USG): Investigation of choice.
  • Confirms fluid presence.
  • Characterizes nature (echogenic, loculated vs free-flowing).
  • Guides drain insertion site.
• CT Chest: Not routine. Indicated only if surgery is planned, to rule out lung abscess, or if malignancy is suspected.

B. Microbiology & Labs

• Pleural Fluid Analysis:
  • Microscopy/Culture: Gram stain and bacterial culture (often negative if prior antibiotics used).
  • PCR/Antigen Detection: Pneumococcal antigen/PCR increases diagnostic yield significantly.
  • Biochemistry: Differentiating exudate vs transudate (Light's criteria) is clinically less useful in pediatric empyema compared to adults.
  • Cytology: Predominant neutrophils (bacterial) vs lymphocytes (TB/malignancy).
• Blood Culture: Positive in ~10–20% of cases; mandatory in all patients.
• Blood Counts: Leukocytosis (neutrophilia), elevated CRP, secondary thrombocytosis (common and benign).

5. Management

A. General Measures

• Admission, oxygen (target SpO2 >92%), analgesia (NSAIDs/Paracetamol), and antipyretics.
• Correction of fluid/electrolyte imbalance.

B. Antibiotic Therapy

• Route: Intravenous initially.
• Choice: Broad-spectrum covering S. pneumoniae and S. aureus.
  • Community-acquired: Cefuroxime or Co-amoxiclav. Add Clindamycin or Vancomycin if MRSA is suspected.
  • Aspiration: Cover anaerobes (Metronidazole/Clindamycin).
• Duration: IV until afebrile and drain removed, followed by oral antibiotics for 1–4 weeks (total 3–6 weeks).

C. Pleural Drainage

• Indications: Moderate to large effusions, respiratory compromise, or failure of antibiotics alone.
• Chest Tube: Small-bore (pigtail) catheters (8–12 Fr) are preferred over large surgical drains (less pain, equal efficacy). Avoid repeated needle aspirations.

D. Intrapleural Fibrinolytics

• Indication: Complicated effusions (loculated/echogenic on USG).
• Agents: Urokinase or Alteplase (tPA).
• Benefit: Breaks down fibrin septations, improves drainage, and significantly shortens hospital stay (BTS Grade A/B evidence).

E. Surgical Management

• Procedures: Video-Assisted Thoracoscopic Surgery (VATS) or Mini-thoracotomy/Decortication.
• Indications:
  • Failure of medical management (antibiotics + drain + fibrinolytics) with persistent sepsis.
  • Organised empyema with thick peel (trapped lung).
  • Bronchopleural fistula.

Prognosis: Excellent in children; complete radiological resolution occurs in most by 3–6 months.