Pneumonia

Definition:

• Inflammation of the substance of the lungs
• It is usually caused by bacterial infection

Classification:

Pneumonia may be classified both anatomically and on the basis of the aetiology

Classification by site:

• Lobar
• Diffuse (bronchopneumonia)

Classification by aetiology;

• Infective (by far the most common)
• Chemical causes (e.g. the aspiration of gastric contents)
• Radiotherapy
• Allergic mechanisms

Note, the last 3 are generally referred to as ‘pneumonitis’

Precipitating factors:

• Viral respiratory infection
• Hospitalized patients
• Smoking
• Alcohol excess
• Bronchiectasis (e.g. in cystic fibrosis)
• Bronchial obstruction (e.g. carcinoma)
• Immunosuppression (e.g. AIDS or treatment with cytotoxic drugs)
• IV drug abuse (frequently associated with Staph. Aureus infection)

Clinical features:

Varies according to the immune status of the patient and the infecting agent. In the most common type of pneumonia (caused by Strep. pneumoniae) there is often:

• Preceding history of viral infection
• High fever (up to 39.5˚C)
• Pleuritic pain
• Dry cough that progresses (after ~ 2 days) to a productive cough with rusty coloured sputum
• Patient breathes rapidly and shallowly
• Decreased chest expansion on the affected side
• A pleural rub

Investigations:

CXR:

• Confirms areas of consolidation
• May show areas of collapse

Blood tests:

• FBC (will show WCC of <4 or >20, may also show polycythaemia if chronic)
• LFTs (some organisms can affect liver function – e.g. Legionella)
• U&Es (signs of dehydration – increased urea/creatinine)
• ESR
• CRP

Arterial blood gas:

• Will usually show hypoxaemia and hypercapnia

Blood culture

Sputum (only useful for proving the existence of an atypical infecting organism)

• Gram stain
• Culture

Types of pneumonia:

• Strep. pneumoniae – very common cause
• Mycoplasma pneumoniae – teens and adults in their 20s
• Haemophilus infuenzae – commonly infects patients with COPD
• Chlamydia psittaci­ – transmitted by infected birds (especially parrots)
• Chlamydia pneumonia – person-to-person transmission
• Staph. aureus – IVDUs and patients with central lines
• Legionella pneumophilia – air-conditioning and shared water systems
• Pneumocystis carinii – immunocompromised (especially AIDS patients)
• Pseudomonas – cystic fibrosis (bad prognostic sign)

Management of pneumonia:

• Antimicrobials (see below for details)
• IV fluids (to rectify dehydration and maintain a good urine output)
• Oxygen
• Analgesia (for pleuritic pain, e.g. NSAIDs)

Antimicrobial treatment of pneumonia:

Community acquired:

• Erythromycin 500mg/6h PO, or
• Clarithromycin 250-500mg BD PO

Hospital acquired:

• COPD/post-influenza:
• Amoxicillin 250-500mg/8h PO

• Aspiration:
• Clindamycin 450-900mg/8h IV, or
• Cefoxitine 2g/8h IV

Complications of pneumonia:

Lung abscesses:

• Common in aspiration pneumonias
• Clinical features:
• Persistent or worsening pneumonia
• Production of large quantities of foul-smelling sputum
• Swinging fever

Empyema:

• This is the presence of pus within the pleural cavity
• Usually arises after the rupture of a lung abscess into the pleural space or from bacterial spread from a severe pneumonia