“An infective inflammatory condition of the lung affecting primarily the alveoli (CAP & HAP)

Risk Factors
  • Modifiable:
    • Smoking
  • Non-Modifiable:
    • Age (>65)
    • Chronic diseases (respiratory and cardiopulmonary conditions)
    • Immunosuppression
    • Impaired airway protection – causing aspiration
Aetiology
  • Community-Acquired:
    • Typical – Streptococcus pneumoniae, haemophilus influenzae, staphylococcus aureus
    • Atypical Bacteria – Mycoplasma pneumoniae, Chlamydophila pneumoniae
    • Viruses – RSV, CMV
  • Hospital-Acquired
    • Gram-ve pathogens – pseudomonas aeruginosa, Enterobacteriaceae
    • Staphylococcus Aurea
    • Streptococcus pneumoniae
Pathophysiology
  1. Failure of protective pulmonary mechanisms (cough reflex, mucociliary clearance, alveolar macrophages)
  2. Pathogen infiltrates pulmonary parenchyma → interstitial and alveolar inflammation
  3. Impaired alveolar ventilation → ventilation/perfusion (V/Q) mismatch with intrapulmonary shunting (right to left)
  4. Hypoxia due to increased alveolar-arterial oxygen gradient
    • Hypoxia is worsened when the affected lung is in the dependent position, as perfusion to the dependent lung is better compared to the nondependent lung.
Clinical Presentation
  • Typical pneumonia is characterised by a sudden onset of symptoms caused by lobar infiltration, including:
    • Severe malaise
    • High fever and chills
    • Productive cough with purulent sputum (yellow-greenish)
      • Crackles and decreased bronchial breath sounds on auscultation
      • Enhanced vocal/tactile fremitus
      • Dullness on percussion
    • Tachypnoea and dyspnoea (nasal flaring, thoracic retractions)
    • Pleuritic chest pain when breathing, often accompanying pleural effusion
    • Pain that radiates to the abdomen and epigastric region (particularly in children)
    • Suspect bacterial pneumonia in immunocompromised patients with acute high fever and pleural effusion
  • Atypical pneumonia typically has a slow course and includes:
    • Nonproductive, dry cough
    • Dyspnea
    • Auscultation often unremarkable
    • Common extrapulmonary features include fatigue, headaches, sore throat, myalgias, and malaise
Investigations
  • Bloods:
    • FBC
    • Inflammatory markers – ↑ CRP, ↑ ESR, leucocytosis
    • ↑ Serum PCT – PCT is an acute phase reactant that can help to diagnose bacterial LRTI
    • ABG – ↓ PaO2 
    • Blood culture
  • Imaging:
    • Chest X-Ray
      • Lobar – Opacity of 1 or more pulmonary lobes, presence of air bronchograms (translucent bronchi inside opaque areas of alveolar consolidations)
      • Bronchopneumonia – poorly defined patchy infiltrates scattered throughout the lungs, presence of air bronchograms)
    • Chest CT – can request if X-Ray in inconclusive.
  • Special:
    • Sputum culture and gram stain
Management
  • Assess the need for hospitalization (clinical judgement and CURB-6)
  • Begin antibiotic therapy based on severity and patient risk factors
  • Provide supportive care – Oxygen, fluids, analgesia, antipyretics
Complications
  • Parapneumonic pleuritis
  • Pleural effusion
  • Pleural empyema
  • Sepsis
  • Respiratory failure
  • ARDS

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