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Community Acquired Pneumonia (CAP)

  • Pneumonia clinically presents as an acute illness with cough, purulent sputum, breathlessness, fever
    • With physical/radiological changes consistent with lung consolidation

Epidemiology/Etiology

  • MC at extremes of ages
  • MCC is pneumococcus overall
  • Iatrogenic (corticosteroids)
  • Other bacteria – M.pneumoniae (young pts) + H.influenza (old pts)
  • Viruses – influenza, HSV, VZV, Measles, CMV
  • Mostly spread by droplets

Pathophysiology

Lobar pneumonia

  • Homogeneous consolidation of ≥1 lobes
  • Stages of inflammation
    • Congestion – alveoli flooded by exudates, neutrophils + RBCs
    • Red hepatisation – fibrin forms on affected lobe (resembles liver)
    • Grey hepatisation – lung tissue becomes grey as congestion resolves
    • Resolution – restoration of normal architecture of lung
  • Most common in elderly

Bronchopneumonia

  • Patchy alveolar consolidation associated with bronchial + bronchiolar inflammation
  • MC in lower lobes and the young
  • Insidious onset

Clinical features

  • Cough – dry/productive/haemoptysis. Sputum is rust-coloured in pneumococcal origin
  • Dyspnoea– as alveoli become filled with pus and debris
  • Fever – swinging fever indicates empyema
  • Pleuritic chest pain – and pleural rub

Chest signs – due to consolidation

  • Percussion – dull
  • Auscultation
    • Bronchial breathing
    • Coarse crackles

Other signs

  • High respiratory rate + pulse rate
  • Low BP
  • Delirium

Extra-pulmonary features

  • Myalgia, arthralgia, malaise
  • Myocarditis, pericarditis – MC in M.pneumoniae (atypical pneumonia)
  • Abdominal pain, diarrhoea, vomiting
  • Labial herpes – MC in pneumococcal

Complications

Immediate

Respiratory failure – PaO2 <80mmHg/6kPa

  • Aim for oxygen sat >92%
  • Do regular ABGs

Hypotension

  • Can be as a result of dehydration and vasodilation due to sepsis
  • Treatment with 250ml of crystalline infusion over 15 mins

Medium-term complications

Pleural effusion – inflam of pleura leads to excess fluid production

  • Symptoms are not present until fluid is >500ml – ↓chest expansion, dullness, ↓breath sounds, pleural rub
  • If fluid becomes infected it can result in empyema
  • Treatment – drainage

Empyema – typically presents in patient who has partially recovered but then develops a spike in temperature

  • Treatment
    • Fluid aspiration – fluid is yellow with low level of glucose
    • Chest drainage
    • Antibiotics – for 4-6 weeks
      • E.g. cefuroxime + co-amoxiclav x 5 days, then metronidazole x 4 weeks (dosages vary according to hospital and patient)

Lobar collapse – most commonly due to sputum retention

Thromboembolism

Pneumothorax

Late complications

Lung abscess – cavitating lesion containing pus

  • MCC is S.aureus, K.pneumoniae
  • Presents as pneumonia that worsens despite treatment – with purulent sputum, fever, malaise, weight loss
  • Investigations
    • CXR – shows walled cavity
    • ↑ESR + CRP
    • Sputum sample
    • Bronchoscopy
  • Gram negative bacteria most likely to progress to pulmonary gangrene
  • Treatment – ABs, drainage, surgical excision (serious cases)

Septicaemia – can result in endocarditis + meningitis

  • Pt has poor systemic symptoms (hypotension, spiking fever, hypovolemia)
  • Treatment – IV Abs

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