Empyema

Infection of the pleural space

Risk factors

• Young or elderly
• Intrinsic lung disease (COPD)
• Diabetes or other immunosuppression
• Alcohol
• IVDU

Aetiology

Primary (complication of lung infection)

• • Parapneumonic
    • Parapneumonic effusions occur in patients with concurrent LRTI or pneumonia
    • Normally an exudate
    • Accompanies and often worsens the pneumonia

Secondary (extrinsic)

• • Trauma
  • Thoracic surgery
    • Bronchopleural fistula predisposes to empyema
    • Management requires evaluation of the underlying cause, drainage of the infection, and obliteration of the residual pleural space
  • Haematologic spread
  • Rupture of a pulmonary or mediastinal abscess
  • Oesophageal perforation

Pathophysiology

• Commonly an exudate
• Occurs after a reactive pleural effusion as a consequence of lung infection (increased vascular permeability, inflammatory cytokines, chemotaxis of neutrophils)
• Microbiology
  • Different flora to pneumonia due to difference in oxygen and pH levels between lung and pleura
  • Staph aureus most common
  • Community-acquired infections are usually gram-positive - strep milleri or strep pneumoniae
  • Hospital infections are most staph or gram negative bacteria
  • Historically associated with streptococcal or pneumococcal pneumonia

Symptoms

• Constitutional symptoms - malaise, fever, loss of appetite
• Cough and dyspnoea
• Chest pain

Natural history

• Progressive process - takes about 4-6 weeks in total

Stage I: exudative phase

• • Fluid associated with an infection, which can easily become infected and lead to the following stages of empyema
  • Signs:
    • Free-floating, serous fluid
    • pH > 7.2, LDH < 1000 U/L, glucose > 60
    • Often no organisms seen/growth on culture, although neutrophils generally high
  • Parapneumonic effusion which is clear and free-floating in the pleural space
  • Pleural fluid is normally sterile and the pH and glucose levels are normal
  • 10F to 14Fm, imaging-guided where possible, is adequate to drain most effusions
  • ACCP indications for insertion of chest drain (as opposed to thoracentesis)
    • Large or loculated effusion
    • Positive cultures
    • pH < 7.2 (means infection 92% accuracy)
    • Pus

Stage II: fibrinopurulent phase

• • Signs
    • Multiloculated effusion, with septa
    • Cloudy or purulent effusion
    • Bacterial colonisation
    • WCC > 500, pH < 7.2, LDH > 1000 U/L, glucose <6
    • Failure of antibiotics and drainage alone
    • Persistent sepsis
    • Variable presentation though
  • The effusion is complicated by loculations (caused by fibrin deposition, activation of the coagulation cascade, and downregulation of the fibrinolytic pathway)
  • 40% treatment failure for chest tube alone; 15% for chest drain and fibrinolytics; 10% for thoracotomy; none for VATS debridement
    • Large, loculated, frankly purulent effusions with positive cultures are less likely to resolve with chest drainage alone
    • VATS has significantly shorter length of stay

Stage III: chronic organising phase

• • Signs:
    • Frank pus or no fluid at all
    • WCC >15,000, pH <7, LDH >1000U/L, glucose <5
    • Pleural cortex
    • Fibrothorax
  • Pleural fluid is turned into frank pus by fibroblast chemotaxis
  • Pleural thickening encases the lung causing restriction, decreased ventilation and perfusion-ventilation mismatch which can lead to a fibrothorax
  • Final stage - not fully reversible even after eradication of the infection
  • Chest drain and antibiotics can remove fluid and control infection, but respiratory impairment requires surgical removal of the peel to restore physiology
  • Can be hard to differentiate from stage II using imaging

Workup

• Aspiration
  • Gold standard for diagnosis is culture of organism
• CXR
• CT
  • Not as good for imaging septations as USS
• USS
  • Can detect loculations reliably
  • Four different patterns - homogenous anechoic (mainly transudative), complex non-septated with internal echogenic foci, complex septated (fibrinopurulent phase empyema), and homogenously echogenic (blood or frank pus)
• PET
  • Not useful

Management

• To follow
• Removal of infected fluid and debridement of pleural space
  • Uncomplicated infections can be drained by ultrasound-guided insertion of a pleural drain (pigtail catheter)
  • Loculated effusions may require more than one catheter
  • Chest tubes may assist in drainage of turbid effusions
  • Fibrinolytic agents can be effective - tPA and Dnase may improve drainage of the pleural space and reduce the need for surgical drainage
  • Macroscopic pus should be treated aggressively with fibrinolysis and surgery
  • VATS decortication - stage II disease, <2 weeks since admission
  • Thoracotomy with debridement or formal decortication - for later stage empyema with persistent dyspnoea, loculations or continued sepsis. Also preferred in gram negative empyema. Necessary whenever adequate decortication cannot be accomplished thoracoscopically.
• Supportive care
  • PT
  • Nutritional support
  • Thromboembolic prophylaxis
• Systemic treatment of the underlying cause of infection
• Full re-expansion of the lung
• Chronic empyema can be treated with drainage, gauze packing, or skin flap (Eloesser flap) with eventual muscle transposition and skin closure. Lung resection of pleuropneumonectomy is rarely required.

Complications

• Lung fibrosis
• Contraction of the hemithorax (fibrothorax)
• Necrosis
• Spontaneous drainage of pus through the chest wall (empyema necessitatis) or into the bronchial tree (bronchopleural fistula)
• Pericarditis
• Mediastinitis
• Osteomyelitis
• Metastatic spread of infection