What is empyema?

What is Empyema?

Empyema is the presence of frank pus in the pleural space, representing an advanced stage of pleural infection that requires drainage in addition to antibiotics. 1

Definition and Clinical Significance

• Empyema is defined as a collection of pus in the pleural cavity, which may be identified by gross purulent appearance, white blood cell count >50,000 WBCs/μL, or positive bacterial culture 1, 2
• This condition represents a serious complication of bacterial pneumonia, occurring in approximately 50% of cases caused by typical bacteria including Streptococcus pneumoniae, Staphylococcus aureus, and β-hemolytic streptococci 1, 3
• Empyema is distinct from simple parapneumonic effusion (clear fluid associated with pneumonia) and represents the most severe end of the pleural infection spectrum 1

The Three-Stage Progression of Pleural Infection

Pleural infection follows a predictable continuum that transforms from a simple fluid collection into empyema: 1, 3

Stage 1: Exudative (Simple Parapneumonic Effusion)

• Clear fluid accumulates with low white cell count in the pleural cavity 1
• Characterized by pH >7.2, LDH <1000 IU/L, glucose >2.2 mmol/L, and negative cultures 1, 2
• This stage typically resolves with antibiotics alone without requiring drainage 1, 2

Stage 2: Fibropurulent (Complicated Parapneumonic Effusion → Empyema)

• Fibrin deposits in the pleural space, creating septations and loculations 1
• White cell counts increase dramatically, fluid thickens, and eventually becomes overt pus (empyema) 1
• pH falls below 7.2, LDH rises above 1000 IU/L, and glucose levels drop 1, 2
• This stage requires chest tube drainage in addition to antibiotics 1, 2

Stage 3: Organizational

• Fibroblasts infiltrate the pleural cavity, forming thick, non-elastic membranes (the "peel") 1, 3
• These fibrous peels prevent lung re-expansion ("trapped lung"), impair lung function, and create persistent infection risk 1
• May lead to chronic empyema, bronchopleural fistula, lung abscess, or empyema necessitans (perforation through chest wall) 1, 4

Key Diagnostic Features

When empyema is suspected based on clinical presentation (prolonged fever, chest pain, respiratory distress): 1

• Chest radiography with lateral decubitus views should confirm pleural fluid presence 1
• Ultrasound is the preferred imaging modality to confirm fluid collection and guide drainage, as it is safer than CT (no radiation) 1, 5
• Frankly purulent or turbid/cloudy fluid on sampling mandates immediate chest tube drainage 2
• For non-purulent effusions, pleural fluid pH <7.2 indicates need for drainage 1, 2

Critical Management Principles

All empyemas require drainage—antibiotics alone are insufficient: 6

• Chest tube drainage is the cornerstone intervention for empyema 6
• Broad-spectrum antibiotics covering aerobic and anaerobic bacteria must be administered concurrently 6
• Fibrinolytic therapy may be considered for complex loculated empyemas, though evidence for routine use remains insufficient 6
• Video-assisted thoracoscopic surgery (VATS) or open thoracotomy is reserved for organized empyema with thick fibrous peel causing trapped lung, or for cases failing medical management 1, 5

Important Clinical Pitfall

If empyema coexists with a lung abscess, drain only the empyema—never drain the lung abscess as initial therapy, as this can cause life-threatening complications. 1, 6 The antibiotics given for empyema will simultaneously treat the lung abscess. 1, 6