Empyema Thoracis

Empyema thoracis is the accumulation of frank pus in the pleural space, arising most commonly as a complication of bacterial pneumonia; the defining biochemical hallmarks are pleural fluid pH below 7.0, glucose below 40 mg/dL, and LDH above 1000 IU/L, and drainage is mandatory because antibiotics alone cannot sterilize an established empyema.

Table of Contents

  1. Pathogenesis: From Parapneumonic to Empyema
  2. Causes and Microbiology
  3. The Three Stages of Empyema
  4. Symptoms and Clinical Presentation
  5. Diagnosis: Pleural Fluid Analysis
  6. Imaging: Ultrasound, CXR, and CT
  7. Treatment: Drainage Strategies
  8. Intrapleural Fibrinolytic Therapy (MIST2 Trial)
  9. Surgical Management and Outcomes
  10. References & Research
  11. Featured Videos

Pathogenesis: From Parapneumonic to Empyema

A parapneumonic effusion is any pleural effusion associated with bacterial pneumonia or a lung abscess, and such effusions occur in approximately 40% of bacterial pneumonias. The progression from simple parapneumonic effusion to frank empyema is a continuum driven by bacterial invasion and the host inflammatory response — not a sudden transition, but a gradual deterioration that can be arrested at early stages with timely intervention.

Simple (Uncomplicated) Parapneumonic Effusion

In the earliest stage, pleural fluid is a sterile exudate — an inflammatory response to adjacent pneumonia, but bacteria have not yet invaded the pleural space. Glucose is normal, pH is above 7.2, and LDH is below 1000 IU/L. Lung fully re-expands after drainage if it is ever needed. Antibiotics alone are sufficient; drainage is not required.

Complicated Parapneumonic Effusion

As bacteria invade the pleural space, the fluid becomes infected or is at very high risk of infection. pH falls to the 7.0–7.2 range, glucose drops to 40–60 mg/dL, and LDH rises markedly. Loculations may begin forming as fibrin is deposited. Drainage is required at this stage — delayed drainage allows progression to frank empyema with fibrin septations that make complete drainage progressively more difficult.

Frank Empyema

Frank empyema is defined by the presence of grossly visible pus in the pleural space, or by biochemical criteria of pH below 7.0, glucose below 40 mg/dL, and LDH above 1000 IU/L, or by positive Gram stain or culture of pleural fluid. Fibrin deposition and loculations are prominent. Organisms are typically demonstrable, though culture may be negative if prior antibiotics have been given. Drainage is mandatory — antibiotics cannot penetrate the organized fibrinous loculations and sterilize the space.

Special Situations

Boerhaave syndrome — spontaneous esophageal rupture — causes mediastinal contamination and empyema through a distinct mechanism: esophageal contents flood the pleural space directly, creating an extremely high-mortality chemical and bacterial pleuritis. The pleural fluid characteristically shows very low pH, elevated amylase (salivary isoform), and may contain food particles. Hematogenous seeding of the pleural space and direct extension from a subphrenic or hepatic abscess across the diaphragm are less common but recognized pathways.

Causes and Microbiology

Pneumonia accounts for 60–70% of empyema cases, with parapneumonic progression as the dominant mechanism. Other important causes include thoracic surgery, trauma, esophageal perforation, and subphrenic abscess.

Causes by Setting

Microbiology: Community-Acquired Empyema

Microbiology: Hospital-Acquired and Post-Surgical Empyema

Culture-Negative Empyema

Up to 40% of microbiologically confirmed empyemas yield negative cultures. Prior antibiotics are the leading explanation — even a single dose significantly reduces culture yield. Fastidious organisms (anaerobes, milleri group) that require special handling or extended incubation also contribute. Culture-negative empyema should still be treated as bacterial empyema with empiric antibiotics guided by clinical context, Gram stain, and setting.

The Three Stages of Empyema

The American Thoracic Society and British Thoracic Society both recognize a three-stage classification that reflects the natural history of pleural infection and guides drainage strategy. The fibrous peel that forms in Stage 3 — organized empyema — wraps the lung and prevents re-expansion, a process called trapped lung.

Stage 1: Exudative (Days 1–3)

The earliest stage features thin, free-flowing pleural fluid with a relatively low cell count. Glucose is normal or near-normal, pH is above 7.2, and LDH is mildly elevated. Bacteria may or may not be demonstrable yet. The lung re-expands fully after drainage. A simple chest tube is often sufficient, and clinical improvement is typically rapid with antibiotics plus drainage. This stage is the window of opportunity — intervention here prevents progression to the fibrinopurulent and organizing stages with their higher morbidity.

Stage 2: Fibrinopurulent (Days 4–14)

The intermediate stage is characterized by thick, turbid pleural fluid with fibrin deposition and the formation of loculations — fibrin strands that divide the pleural space into multiple compartments that cannot all be drained by a single tube. Glucose is low, pH falls to the 7.0–7.2 range, LDH is markedly elevated, and bacteria are typically present on Gram stain or culture. A single chest tube is frequently insufficient because loculations prevent complete drainage. Intrapleural fibrinolytic therapy (tPA plus DNase) is most effective in this stage. VATS is also highly effective and preferred for patients who can tolerate general anesthesia.

Stage 3: Organizing (>14 Days)

The late stage features frank thick pus with extensive fibrin deposition forming a "pleural peel" — a thick, leathery rind covering both the visceral and parietal pleural surfaces. The lung is encased and cannot re-expand after drainage, resulting in a "trapped lung" with persistent pleural space and respiratory restriction. Paradoxically, bacteria may be absent at this stage (sterile empyema) because the inflammatory process has been sustained beyond bacterial clearance. Surgical decortication — stripping the parietal and visceral peel to free the lung — is required for lung re-expansion and may involve open thoracotomy.

Symptoms and Clinical Presentation

Empyema thoracis most commonly presents as a pneumonia that is not improving or is worsening despite apparently appropriate antibiotics — a pattern that should immediately prompt consideration of pleural complication and thoracentesis.

Physical Examination

Examination shows dullness to percussion over the effusion, reduced or absent breath sounds, and reduced chest expansion on the affected side. In large empyemas, tracheal deviation away from the affected side may be present. Fever, tachycardia, and an ill-appearing patient complete the picture. Empyema may be clinically indistinguishable from a large simple parapneumonic effusion on examination — the diagnosis requires imaging and thoracentesis.

Diagnosis: Pleural Fluid Analysis

No empyema diagnosis is complete — or treatment properly directed — without thoracentesis and pleural fluid analysis. Ultrasound-guided thoracentesis reduces the risk of pneumothorax and failed procedures and should be used whenever available.

Fluid Appearance

Frankly purulent fluid — thick, opaque, yellow-green pus — establishes the diagnosis of empyema by definition regardless of biochemical values. Turbid or cloudy fluid is suspicious and should prompt full biochemical evaluation. Clear straw-colored fluid is unlikely to be empyema but may still represent complicated parapneumonic effusion if the biochemical values are abnormal.

Pleural Fluid pH: The Most Important Single Test

Pleural fluid pH is the single most important biochemical determinant of whether drainage is needed. pH below 7.2 indicates a complicated parapneumonic effusion or empyema and mandates drainage. pH below 7.0 is consistent with frank empyema. The pH must be measured on a blood gas analyzer — colorimetric pH strips are unreliable in pleural fluid and should never be used. The specimen must be transported in a heparin blood gas syringe on ice and processed immediately; prolonged room-temperature storage causes falsely low pH readings due to ongoing cellular metabolism in the sample.

Glucose, LDH, and Protein

Glucose below 40 mg/dL strongly suggests empyema or complicated parapneumonic effusion (also seen in rheumatoid pleuritis and malignant effusion). LDH above 1000 IU/L is a strong indicator of complicated pleural infection. Protein is used in Light's criteria to confirm that the fluid is an exudate: pleural protein/serum protein ratio above 0.5, pleural LDH/serum LDH ratio above 0.6, or pleural LDH above two-thirds of the upper limit of normal for serum LDH — meeting any one criterion defines an exudate.

Gram Stain and Culture

Gram stain is positive in 50–60% of culture-positive cases and provides early guidance for antibiotic selection. Culture must include both aerobic and anaerobic bottles — inoculating blood culture bottles at the bedside immediately after thoracentesis significantly increases yield compared to transport in a plain tube. Prior antibiotic administration reduces culture yield by 40–50%, which is a major clinical problem since most patients have already received antibiotics by the time thoracentesis is performed.

Cell Count, Cytology, and Special Tests

Neutrophil predominance confirms bacterial infection. Lymphocyte predominance should prompt consideration of tuberculosis or malignancy. Cytology is sent to exclude malignant effusion when clinical suspicion exists. Amylase elevation in pleural fluid is diagnostically important — it indicates esophageal perforation (salivary amylase isoform) or pancreatitis-related effusion (pancreatic isoform), both of which require distinct management.

Decision Framework

The modified Light's decision framework for drainage: pH below 7.2, glucose below 60 mg/dL, positive Gram stain or culture, or frankly purulent fluid → drain immediately. pH 7.2–7.3 is borderline — repeat thoracentesis, clinical judgment, and CT imaging are required. A frankly purulent appearance overrides all biochemical values.

Imaging: Ultrasound, CXR, and CT

Each imaging modality contributes distinct information to empyema diagnosis and management. The standard approach is chest X-ray for initial detection, ultrasound for procedure guidance and loculation assessment, and CT for definitive staging and planning of intervention.

Chest X-ray

Chest X-ray demonstrates blunting of the costophrenic angle (requiring at least 200 mL of fluid), homogeneous ipsilateral opacity, and possible pleural thickening. Multiple air-fluid levels suggest loculation or bronchopleural fistula. Chest X-ray cannot reliably distinguish empyema from a simple transudative effusion or detect early loculations — these limitations are why ultrasound and CT are essential adjuncts.

Ultrasound

Bedside ultrasound is superior to chest X-ray for detecting loculations, which appear as echogenic strands and fibrin septations dividing the pleural space. The echogenicity and complexity of the fluid on ultrasound correlate with the fibrin content and thus with the fibrinopurulent stage — a finding that predicts need for fibrinolytic therapy or VATS. Ultrasound guides safe thoracentesis and chest tube placement with real-time needle visualization, particularly important in patients with coagulopathy or challenging anatomy. Ultrasound cannot fully characterize a pleural peel or assess the underlying lung for abscess, malignancy, or bronchial obstruction.

CT Chest with Contrast

Contrast-enhanced CT is the gold standard for empyema evaluation and staging. Key findings include:

FDG-PET

FDG-PET is not part of routine empyema evaluation but is used when malignant mesothelioma enters the differential diagnosis — particularly in cases of chronic empyema, extensive pleural thickening, or unexplained pleural disease without a clear infectious cause.

Treatment: Drainage Strategies

Antibiotic therapy is necessary but fundamentally insufficient as the sole treatment for established empyema. Drainage of the infected pleural space is the cornerstone of management; the choice of drainage method is determined by the stage of empyema and the degree of loculation on imaging.

Antibiotics

Empiric antibiotic selection is guided by the clinical setting, with adjustment once culture results are available. Total duration is typically 3–6 weeks:

Small-Bore Chest Tube (Pigtail, 12–14 Fr)

Ultrasound-guided small-bore chest tube insertion is adequate for free-flowing Stage 1 exudative empyema and is associated with less pain and immobility than large-bore tubes. The limitation is that the small lumen occludes readily with thick pus or fibrin, and a single small-bore tube cannot drain a loculated Stage 2 empyema. The 2015 BTS trial (Rahman et al.) demonstrated that small-bore tube plus intrapleural fibrinolytics (tPA+DNase) was not inferior to large-bore tube for non-loculated empyema, and produced better outcomes in the combined fibrinolytic arm.

Large-Bore Chest Tube (28–32 Fr)

Traditional large-bore chest tubes allow drainage of thick pus and were historically the standard. Their disadvantages — significant pain, patient immobility, and inability to drain loculations — have made them less preferred compared to small-bore tube plus fibrinolytics for non-surgical candidates. Large-bore tubes may still be required when pus is extremely viscous or when small-bore tubes repeatedly occlude.

Monitoring Drainage Response

Daily fluid output from the chest tube, serial CXR or ultrasound, and clinical trajectory (fever, CRP, inflammatory markers) guide the decision to escalate to fibrinolytic therapy or VATS when tube drainage alone is insufficient. Failure criteria include persistent fever beyond 5–7 days of drainage, stagnant or increasing fluid on imaging, or clinical deterioration.

Intrapleural Fibrinolytic Therapy (MIST2 Trial)

Intrapleural fibrinolytic therapy targets the fibrin loculations and viscous neutrophil debris that prevent complete drainage in Stage 2 fibrinopurulent empyema. The MIST2 trial established the combination of tissue plasminogen activator (tPA) with DNase as the evidence-based standard.

Scientific Rationale

Fibrin septations — produced by the procoagulant state of the infected pleural space — physically divide the pleural space into isolated pockets that a single drainage tube cannot reach. Tissue plasminogen activator dissolves fibrin directly. DNase (dornase alfa) degrades the extracellular DNA released by degenerating neutrophils, which substantially contributes to pleural fluid viscosity independent of fibrin content. Animal studies showed that each agent alone had modest effect on the viscous, loculated material of Stage 2 empyema, but the combination was synergistic.

MIST2 Trial (Rahman et al., NEJM 2011)

The Multicenter Intrapleural Sepsis Trial 2 enrolled 210 patients with radiologically confirmed pleural infection randomized to four arms: tPA plus DNase, tPA alone, DNase alone, or double placebo. The primary endpoint was change in pleural opacity on chest X-ray at day 7. The tPA plus DNase combination was significantly superior to placebo on all outcomes: greatest reduction in radiographic opacity, lowest surgical referral rate (approximately 5% vs. 30% for placebo), and shortest hospital stay. Neither tPA alone nor DNase alone was superior to placebo — the combination is essential, not either agent individually. This trial directly changed international practice guidelines.

Standard Dosing Regimen

tPA 10 mg plus DNase 5 mg instilled via the chest tube twice daily for 3 days (6 doses total). Each dose is administered with a 1-hour tube clamp period to allow distribution within the pleural space, followed by reopening for drainage. The agents are prepared separately and instilled sequentially (not mixed).

Contraindications

Bronchopleural fistula (BPF) is an absolute contraindication — tPA instilled into a pleural space that communicates with the airways will flood the bronchial tree and cause massive hemoptysis or respiratory failure. An air leak through the chest tube is the clinical sentinel of BPF and mandates CT evaluation before fibrinolytics are administered. Additional contraindications include active systemic bleeding, recent surgery (within 2 weeks), and significant coagulopathy.

Surgical Management and Outcomes

Surgery is indicated when tube drainage with or without fibrinolytics fails to adequately drain the empyema, when the Stage 3 organizing empyema has formed a lung-entrapping pleural peel, or when VATS is chosen as first-line invasive therapy for fit patients with Stage 2 disease.

VATS (Video-Assisted Thoracoscopic Surgery)

VATS is the preferred surgical approach for empyema. Through 3–4 port incisions, the thoracoscope and instruments allow direct visualization of the pleural space, debridement of fibrin deposits and septations, disruption of early loculations, and drain placement under direct vision. VATS is most effective in Stage 2 fibrinopurulent empyema before a fully organized peel has formed — at this stage, the fibrin can be broken down and removed without requiring formal decortication. The minimally invasive approach reduces postoperative pain and recovery time compared to open thoracotomy. CHEST Society guidelines recommend VATS as a preferred approach for patients who can tolerate general anesthesia with Stage 2 empyema; UK practice (BTS guidelines) favors a fibrinolytic-first strategy with VATS reserved for fibrinolytic failure.

Open Decortication (Thoracotomy)

Open decortication is required for Stage 3 organizing empyema with a mature pleural peel. Through a standard thoracotomy incision, the surgeon strips the parietal and visceral peel from the chest wall and lung surface, respectively, freeing the trapped lung and allowing it to re-expand to fill the hemithorax. This is a major operation with significant morbidity — bleeding from the raw decorticated surfaces, prolonged air leak from the visceral pleura, and respiratory complications are common. Rib resection may be required in cases of extreme fibrosis. Despite the morbidity, decortication may be the only route to lung re-expansion and resolution of the chronic septic focus in Stage 3 disease.

Open-Window Thoracostomy (Eloesser Flap)

In patients who cannot tolerate definitive surgery — the very elderly, severely debilitated, or those with major cardiopulmonary comorbidity — open-window thoracostomy creates a permanent opening in the chest wall by resecting a segment of rib. The resulting window allows chronic open drainage of the empyema cavity and avoids the risks of general anesthesia and thoracotomy. This is a palliative approach that controls the septic focus without achieving lung re-expansion; the cavity granulates slowly over months.

Outcomes

Mortality from community-acquired empyema in adults ranges from 10–20%, reflecting the underlying severity of the pneumonia and patient comorbidities rather than the empyema alone. Hospital-acquired empyema, particularly MRSA or gram-negative pleural infections in post-surgical patients, carries substantially higher mortality. Elderly patients and those with malignancy, renal failure, or immunosuppression have significantly worse outcomes. Children with community-acquired empyema — predominantly pneumococcal — have excellent outcomes, with survival above 95% and full lung recovery in the majority. Failure to achieve lung re-expansion results in chronic fibrothorax and permanent restrictive ventilatory deficit.

References & Research

Key Research Papers

  1. Rahman NM, Maskell NA, West A, et al. Intrapleural use of tissue plasminogen activator and DNase in pleural infection. N Engl J Med. 2011;365(6):518-526. PMID 21830966
  2. Davies HE, Davies RJ, Davies CW; BTS Pleural Disease Guideline Group. Management of pleural infection in adults: British Thoracic Society Pleural Disease Guideline 2010. Thorax. 2010;65(Suppl 2):ii41-53. PMID 20696693
  3. Light RW, Macgregor MI, Luchsinger PC, Ball WC Jr. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med. 1972;77(4):507-513. PMID 4642731
  4. Maskell NA, Davies CW, Nunn AJ, et al. U.K. Controlled trial of intrapleural streptokinase for pleural infection. N Engl J Med. 2005;352(9):865-874. PMID 15745977
  5. Piccolo F, Popowicz N, Wong S, Lee YC. Intrapleural tissue plasminogen activator and deoxyribonuclease therapy for pleural infection. J Thorac Dis. 2015;7(6):999-1008. PMID 26150912
  6. Colice GL, Curtis A, Deslauriers J, et al. Medical and surgical treatment of parapneumonic effusions: an evidence-based guideline. Chest. 2000;118(4):1158-1171. PMID 11035692
  7. Wrightson JM, Davies HE. Outcome of patients with empyema undergoing medical or surgical treatment. Curr Opin Pulm Med. 2008;14(4):375-380. PMID 18520269
  8. Rahman NM, Chapman SJ, Davies RJ. Pleural effusion: a structured approach to care. Br Med Bull. 2004;72:31-47. PMID 15767566
  9. Sahn SA, Light RW. The sun should never set on a parapneumonic effusion. Chest. 1989;95(5):945-947. PMID 2707576
  10. Idell S. Coagulation, fibrinolysis, and fibrin deposition in acute lung injury. Crit Care Med. 2003;31(4 Suppl):S213-220. PMID 12682443
  11. Hamm H, Light RW. Parapneumonic effusion and empyema. Eur Respir J. 1997;10(5):1150-1156. PMID 9163661
  12. Lee SF, Lawrence D, Booth H, Morris-Jones S, Macrae MB, Brown J. Thoracic empyema: current opinions in medical and surgical management. Curr Opin Pulm Med. 2010;16(3):194-200. PMID 20179609

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Research Papers

The following PubMed topic searches retrieve current peer-reviewed literature on Empyema Thoracis. Each link opens a live PubMed query.

  1. Empyema thoracis pleural infection treatment
  2. Intrapleural tPA DNase fibrinolytic therapy
  3. VATS empyema decortication surgical outcome
  4. Parapneumonic effusion drainage pH criteria
  5. Pleural fluid Light's criteria exudate diagnosis
  6. Empyema Streptococcus milleri group loculation
  7. Split pleura sign CT empyema diagnosis
  8. Bronchopleural fistula empyema management
  9. Pediatric empyema pneumococcal outcome
  10. Boerhaave syndrome esophageal perforation empyema

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Connections

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