Parapneumonic Pleural Effusion and Empyema

15-mark MD examination answer

Definition

Importance and epidemiology

• Up to 40% of hospitalized patients with bacterial pneumonia have an associated pleural effusion.
• Pneumonia with a pleural effusion is associated with greater morbidity and mortality than pneumonia alone.
• In hospitalized community-acquired pneumonia, patients with pleural effusion were 2.7 times more likely to fail treatment.
• Bilateral effusions and moderate-to-large unilateral effusions increase mortality risk.
• Although most effusions resolve without pleural intervention, about 10% require operative intervention.
• Delay in appropriate drainage increases morbidity because a free-flowing effusion can become loculated and difficult to drain within 12-24 hours.

Pathogenesis and stages

1. Exudative stage

• Rapid accumulation of sterile pleural fluid.
• Fluid probably arises mainly from the lung interstitial spaces, with possible contribution from increased permeability of visceral pleural capillaries due to adjacent pneumonitis.
• Pleural fluid shows:
  • Low white-cell count
  • Low LDH
  • Normal glucose
  • Normal pH
• Appropriate antibiotic treatment at this stage prevents progression.
• Chest-tube drainage is usually unnecessary.

2. Fibropurulent stage

• If infection is inadequately treated, bacteria invade the pleural space.
• There is accumulation of:
  • Large amounts of pleural fluid
  • Polymorphonuclear leukocytes
  • Bacteria
  • Cellular debris
• Fibrin is deposited over visceral and parietal pleura.
• Fibrin membranes lead to septation and loculation.
• Loculi restrict spread of infection but make effective drainage difficult.

3. Organizing stage

• Fibroblasts grow into fibrinous pleural membranes.
• A thick pleural peel develops, encasing the lung.
• The lung becomes restricted and fails to expand adequately.
• Decortication may be needed in selected patients.

Bacteriology

Important organisms

• Aerobic gram-positive organisms
  • Staphylococcus aureus
  • Streptococcus pneumoniae
  • Streptococcus pyogenes
• Gram-negative organisms
  • Escherichia coli
  • Klebsiella species
  • Pseudomonas species
  • Haemophilus influenzae
• Anaerobes
  • Bacteroides species
  • Peptostreptococcus

• Aerobic organisms are isolated slightly more often than anaerobes.
• Gram-positive aerobes are isolated about twice as often as gram-negative aerobes.
• Anaerobic infection should be suspected with a foul or feculent smell of pleural fluid.
• Pleural fluid cultures are often negative, even in frank pus.
• Direct inoculation of pleural fluid into blood-culture bottles at thoracentesis improves microbiological yield.

Clinical features

Symptoms and signs

• Fever
• Pleuritic chest pain
• Cough with sputum production
• Leukocytosis
• Persistent fever for more than 48 hours after starting antibiotics
• Failure to improve clinically after 48-72 hours of antimicrobial therapy
• In debilitated patients or those receiving corticosteroids, empyema may be relatively asymptomatic or afebrile.

When to suspect complicated PPE

• Persistent toxicity or fever despite antibiotics
• Loculated pleural fluid
• Pleural effusion increasing in size
• Persistent significant effusion after treatment
• Foul-smelling fluid
• Positive Gram stain or culture
• Low pH or low glucose
• Elevated LDH

Diagnosis

1. Chest radiography

• Lateral chest radiograph may show blunting of the posterior costophrenic angle or obscuration of a hemidiaphragm.
• If both diaphragms are clearly visible and the posterior costophrenic angle is not blunted, significant free pleural fluid is unlikely.

2. Decubitus radiograph

• Helps assess whether fluid is free-flowing and estimates its size.
• If pleural fluid thickness is less than 10 mm, it is usually clinically insignificant and thoracentesis is not required.

3. Ultrasonography

• Portable and useful in critically ill or ICU patients.
• Detects pleural fluid.
• Identifies septations and loculations.
• Guides thoracentesis and catheter placement.

4. CT chest

• Confirm pleural fluid.
• Assess the amount of fluid.
• Identify loculations.
• Differentiate pleural fluid from parenchymal opacity.
• Assess inadequate drainage and residual collections.

5. Diagnostic thoracentesis

• Gross appearance and odor
• Cell count
• Gram stain
• Aerobic and anaerobic culture
• pH, measured using a blood gas machine
• Glucose
• LDH

Pleural fluid indicators of poor prognosis and need for drainage

1. Frank purulent pleural fluid
2. Feculent odor, suggesting anaerobic infection
3. Positive Gram stain
4. Positive culture
5. pH below 7.20, especially below 7.00
6. Low pleural-fluid glucose
7. High pleural-fluid LDH, especially more than three times the upper normal serum limit
8. Loculated fluid collection

Important caveats

• pH must be measured in a blood gas analyser. Indicator paper or standard pH meters are insufficiently accurate.
• In loculated PPE, pH can differ markedly between locules.
• In infection with Proteus species, pleural pH may be unusually high because these organisms produce ammonia through urea splitting.

Light’s classification of parapneumonic effusions

ACCP risk categories

Category 1

• Minimal, free-flowing effusion, less than 10 mm.
• Very low risk of poor outcome.
• Drainage not required.

Category 2

• Small-to-moderate, free-flowing effusion.
• More than 10 mm but less than half the hemithorax.
• Gram stain and culture negative.
• pH more than 7.20.
• Low risk.
• Drainage not required.

Category 3

• Effusion occupying more than half the hemithorax
• Loculated fluid
• Thickened parietal pleura
• Positive Gram stain or culture
• pH less than 7.20
• Glucose less than 60 mg/dL

Category 4

• Frank pus in pleural fluid.
• High risk of poor outcome.
• Drainage is mandatory.

Management

1. Appropriate antimicrobial treatment
2. Adequate management and drainage of pleural fluid

A. Antibiotic therapy

• Antibiotic choice should consider likely organisms and penetration into pleural fluid.
• Anaerobic coverage is recommended in all PPE using clindamycin or metronidazole.
• Health-care-associated pleural infection requires coverage for gram-negative enteric organisms and MRSA.
• If Pseudomonas infection is suspected, an antipseudomonal agent such as piperacillin, piperacillin-tazobactam, imipenem, meropenem, or cefepime should be included.
• There is no reason to increase antibiotic dosage merely because an effusion is present.

B. Pleural fluid management

1. Observation

• Free-flowing
• Less than 10 mm thick
• Patient clinically improving on antibiotics

2. Therapeutic thoracentesis

• Initial thoracentesis should be therapeutic if adequate fluid is present.
• If fluid reaccumulates without adverse prognostic factors and the patient is improving, further intervention may not be needed.
• If fluid reaccumulates with poor prognostic features, repeat therapeutic thoracentesis is indicated.
• If it reaccumulates again, tube thoracostomy is appropriate.

3. Tube thoracostomy

• Frank pus
• Positive Gram stain or culture
• pH below 7.00
• Glucose below 40 mg/dL
• Significant infected or complicated effusion
• Inadequate response to thoracentesis

• Place tube in the dependent part of the collection.
• Initially connect to underwater-seal drainage.
• Small-bore catheters can be effective and cause less pain than large-bore tubes.
• If drainage is inadequate, obtain CT to identify malposition, undrained locules, or a restrictive fibrinous peel.
• Remove tube when drainage is less than 50 mL per 24 hours, fluid is clear yellow, and daily sediment is less than 5 mL.

4. Intrapleural therapy

• Fibrinolytics alone, such as streptokinase, have not shown routine benefit.
• tPA plus DNase is superior to either agent alone or placebo.
• The PDF recommends, when this approach is chosen, tPA 10 mg plus DNase 5 mg intrapleurally twice daily for 3 days.
• Rarely, intrapleural fibrinolytic treatment can cause hemothorax.

5. Video-assisted thoracoscopic surgery (VATS)

• Incomplete drainage after chest tube
• Persistent multiloculated collection
• Failure of less invasive treatment
• Need for lysis of adhesions and possible decortication

6. Decortication

• Removes fibrous tissue from visceral and parietal pleura and evacuates pus.
• Eliminates pleural sepsis and permits lung re-expansion.
• May be performed by VATS or open thoracotomy.
• If decortication is needed, it should be performed within 10-14 days of initial recognition of PPE.
• It should be done for control of pleural infection and trapped lung, not merely because pleura is thickened, since pleural thickening often resolves spontaneously over months.

7. Open drainage

Practical management algorithm

1. Pneumonia with pleural fluid: assess with radiograph, ultrasound, and/or CT.
2. Fluid <10 mm and free flowing: antibiotics alone.
3. Fluid >10-20 mm or clinically significant: image-guided diagnostic and therapeutic thoracentesis.
4. Pus, positive Gram stain/culture, pH <7.00, glucose <40 mg/dL, or persistent infected fluid: chest-tube drainage plus antibiotics.
5. Loculated effusion with poor prognostic features: VATS if patient is an operative candidate, or chest tube with intrapleural tPA plus DNase.
6. Persistent incomplete drainage or failure of lung expansion: VATS and/or decortication.
7. Do not continue an ineffective treatment for more than 1-2 days before escalating treatment.

Conclusion