Pneumonia

“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 – ↓ P_aO₂ 
  • 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