5.9 Pleural Disease, Empyema & Pneumothorax

Light's Criteria for Exudative Effusion

A pleural effusion is classified as an EXUDATE if it meets AT LEAST ONE of the following three criteria:

1. Pleural Fluid Total Protein / Serum Total Protein ratio > 0.5
2. Pleural Fluid LDH / Serum LDH ratio > 0.6
3. Pleural Fluid LDH > 2/3 the Upper Limit of Normal (ULN) for the laboratory's serum LDH reference range

(If all 3 criteria are absent, the effusion is definitively a TRANSUDATE; sensitivity for exudate is ~98%).

The "Pseudoexudate" in Diuresed Heart Failure

• In patients with congestive heart failure who receive aggressive loop diuretic therapy, water is cleared from the pleural space faster than protein and LDH, concentrating the pleural fluid and falsely fulfilling Light's criteria for an exudate in ~20% of cases.
• To identify a pseudoexudate, calculate the Serum-to-Pleural Fluid Albumin Gradient: $\text{Gradient} = \text{Serum Albumin} - \text{Pleural Fluid Albumin}$
• If the Albumin Gradient > 1.2 g/dL (or Serum Total Protein - Pleural Total Protein > 3.1 g/dL), the effusion is confirmed to be a transudate secondary to heart failure, and invasive workup for exudative causes can be avoided.

Etiologic Classification & Diagnostic Pleural Fluid Patterns

1. Parapneumonic Effusions and Empyema

Parapneumonic effusions develop in up to 40% of patients hospitalized with bacterial pneumonia and require immediate risk stratification to determine the necessity of tube thoracostomy.

Three-Tier Staging & Management Protocol

1. Uncomplicated Parapneumonic Effusion:
   • Pleural Fluid Findings: Clear/turbid fluid, pH > 7.20, Glucose > 60 mg/dL, LDH < 1000 IU/L, negative Gram stain and culture.
   • Management: Systemic IV Antibiotics alone. Does not require tube drainage; resolves with treatment of the underlying pneumonia.
2. Complicated Parapneumonic Effusion:
   • Pathogenesis: Direct bacterial invasion of the pleural space, leading to accelerated anaerobic glycolysis (producing lactic acid) and neutrophil lysis.
   • Pleural Fluid Findings: pH < 7.20, Glucose < 60 mg/dL, LDH > 1000 IU/L, +/- positive Gram stain or culture, loculations/septations on ultrasound.
   • Management: Prompt Tube Thoracostomy (Chest Tube Drainage) + Systemic IV Antibiotics. Antibiotic penetration into an undrained acidic pleural space is inadequate; delaying drainage leads to extensive pleural organization, trapping, and high mortality.
3. Empyema:
   • Pleural Fluid Findings: Frank, visible pus in the pleural space, or presence of visible bacteria on Gram stain or bacterial growth on culture.
   • Management: Immediate Tube Thoracostomy + IV Antibiotics.

Management of Loculated / Non-Draining Pleural Infection

• If chest tube drainage is incomplete due to thick fibrinous loculations and multi-septated fluid:
• Intrapleural Fibrinolytic and Enzyme Therapy (MIST-2 Trial): Combination of intrapleural tissue Plasminogen Activator (tPA 10 mg) PLUS recombinant human Deoxyribonuclease (DNase 5 mg) administered twice daily via the chest tube for 3 days (6 doses total). The landmark MIST-2 trial demonstrated that tPA + DNase significantly improves radiographic pleural clearance, reduces the requirement for surgical decortication, and shortens hospital stay (neither agent alone was effective).
• If intrapleural tPA/DNase fails or thick pleural peel creates a trapped lung: Video-Assisted Thoracoscopic Surgery (VATS) decortication.

2. Pneumothorax: Classification & Emergency Triage

Primary Spontaneous Pneumothorax (PSP)

• Etiology: Rupture of apical subpleural blebs or bullae in patients without underlying lung disease. Classic patient is a tall, thin young male (15–34 years) with a history of cigarette smoking.
• Management:
  • Small (<2–3 cm rim at apex / <2 cm at hilum) and clinically stable: High-flow supplemental oxygen (increases pleural nitrogen washout, accelerating air reabsorption by 4-fold) and observation for 4–6 hours with repeat chest radiograph before discharge.
  • Large (>=2–3 cm) or symptomatic: Simple needle aspiration (16–18G angiocatheter) or small-bore (<=14F) chest tube / pigtail catheter.
  • Recurrent PSP: VATS pleurodesis (mechanical/talc) and apical wedge resection.

Secondary Spontaneous Pneumothorax (SSP)

• Etiology: Occurs in patients with known underlying lung disease (COPD/emphysema bullae, Pneumocystis jirovecii pneumonia [PJP], cystic fibrosis, necrotizing bacterial pneumonia, lymphangioleiomyomatosis [LAM]).
• Management: Because patients have limited pulmonary reserve, SSP is potentially life-threatening. Tube thoracostomy (chest tube drainage) is required for virtually all patients regardless of size, followed by definitive pleurodesis.

Tension Pneumothorax: Emergency Resuscitation

• Pathophysiology: A one-way "ball-valve" mechanism allows air to enter the pleural space during inspiration but prevents egress during expiration -> intrapleural pressure exceeds atmospheric pressure throughout the respiratory cycle -> ipsilateral total lung collapse -> mediastinal and tracheal shift to the contralateral side -> compression of the superior/inferior vena cava and right atrium -> catastrophic reduction in venous return -> obstructive shock, electromechanical dissociation (PEA), and death.
• Clinical Signs: Severe respiratory distress, cyanosis, hypotension, tachycardia, tracheal deviation AWAY from the affected hemithorax, unilateral absent breath sounds, and hyperresonance to percussion.
• EMERGENCY ACTION RULE: Tension pneumothorax is a PURELY CLINICAL DIAGNOSIS. NEVER DELAY TREATMENT TO OBTAIN A CHEST RADIOGRAPH.
• Immediate Intervention: Emergent Needle Decompression using a large-bore (14–16 gauge, >=5 cm length) angiocatheter inserted into the 2nd intercostal space in the midclavicular line or the 4th/5th intercostal space in the anterior axillary line on the affected side. Decompression immediately converts tension pneumothorax into a simple open pneumothorax and must be followed immediately by definitive Tube Thoracostomy (chest tube insertion).