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Lung Abscess (Ch. 18)

Definition and Overview

  • Lung abscess: necrosis of lung tissue leading to a localized air- and fluid-filled cavity; pus contains WBCs, proteins, and tissue debris.
  • Early stage: indistinguishable from pneumonia; late stage: anatomic alterations resemble TB.
  • Commonly forms in the lower lobes and posterior segments of the upper lobes.
  • Most often a complication of aspiration pneumonia.

Etiology

  • Aspiration of oral and gastric fluids
  • Bullae and cysts
  • Penetrating chest wounds
  • Bronchial obstruction (tumor or foreign body) with secondary cavitating infection
  • Interstitial lung disease with cavity formation
  • Vascular obstruction with tissue infarction (septic embolism)

Anatomic Alterations

  • Alveolar consolidation (similar to pneumonia)
  • Alveolar-capillary and bronchial wall destruction
  • Tissue necrosis with potential rupture into a bronchus or intrapleural space
  • Cavity formation
  • Fibrosis and calcification of lung parenchyma
  • Bronchopleural fistulas and empyema
  • Atelectasis
  • Excessive airway secretions
  • Broncholithiasis may occur; bronchospasm can close affected bronchi
  • Note: patterns are similar to TB in some aspects

Radiologic Findings

  • Chest radiograph: increased opacity
  • Cavity formation
  • Cavities with air-fluid levels
  • Fibrosis and calcification
  • Pleural effusion

Clinical Manifestations

  • Increased heart rate (HR), respiratory rate (RR), and blood pressure (BP)
  • Chest pain and reduced chest expansion
  • Cyanosis
  • Cough with sputum production; hemoptysis
  • Chest exam: increased tactile fremitus and vocal fremitus; dull percussion over abscess; bronchial breath sounds; diminished breath sounds
  • Pleural friction rub if abscess is near pleural surface
  • Whispered pectoriloquy

Pulmonary Function Tests (PFTs)

  • Severe/extensive disease (restrictive physiology)
    • Reduced lung volumes and reduced flow rates
    • Pattern may show decreased FVC, FEV1, and related indices; FEV1/FVC often normal or increased
    • Reduced MVV and related expiratory flows
  • Moderate to severe (restrictive)
    • Decreased VT, IRV, ERV, RV, VC, IC, FRC, TLC
    • RV/TLC ratio may be affected (variable)

Arterial Blood Gases (ABG)

  • Mild to moderate abscess (acute alveolar hyperventilation with hypoxemia; acute respiratory alkalosis)
    • pH: up; PaCO2: down; HCO3-: near normal
    • PaO2: down; SaO2/SpO2: down
  • Severe abscess (acute ventilatory failure with hypoxemia; acute respiratory acidosis)
    • pH: down; PaCO2: up; HCO3-: up or normal
    • PaO2: down; SaO2/SpO2: down

Abnormal Laboratory Tests

  • Sputum culture typically shows anaerobic organisms:
    • Gram-positive cocci: Peptostreptococci, Peptococci
    • Anaerobic gram-negative bacilli: Bacteroides fragilis, Prevotella melaninogenica, Fusobacterium spp.

Radiologic Correlates (Summary)

  • Chest radiograph findings mirror the clinical course: opacity, cavity formation, air-fluid levels, and possible fibrosis/calcification or effusion.

General Management

  • Treatment guided by severity
  • Intravenous antimicrobial therapy coupled with prompt drainage and surgical debridement when indicated
  • Various antibiotics are used (based on likely organisms and patient factors)

Respiratory Care Treatment Protocols

  • Oxygen Therapy Protocol
  • Bronchopulmonary Hygiene Therapy Protocol
  • Lung Expansion Therapy Protocol

Differential and Imaging Considerations

  • Reactivation tuberculosis can present with cavitary lesions and air-fluid levels, requiring differentiation from lung abscess during evaluation (clinical context and microbiology guide management)