Pneumonia• Acute inflammation of lung parenchyma

• Inflammatory infiltrate in alveoli

( = consolidation)

CLASSIFICATION:

Aetiology.

Morpological class. - Bronchopneumonia vs. lobar

pneumonia.

Community acquired vs hospital acquired

(nosocomial) infection.

The patient's immune status.

AETIOLOGY

• Bacteria, viruses, fungi, mycoplasma,chlamydia.

• Microbiological identification of organism often

not possible.

• Previously healthy individual:

→ S. pneumoniae

• Pre-existing viral infection

→ Staph. aureus or S. pneumoniae

• Chronic bronchitis

→ Haemophilus influenzae or S. pneumoniae

• AIDS

→ Pneumocystis carinii, cytomegalovirus, TB

Morphological classification

- Bronchopneumonia

- Lobar pneumonia

Bronchopneumonia:

• Infants + young children and the elderly.

• Usually secondary to other conditions associated with local and

general defence mechanisms:

- viral infections (influenza, measles)

- aspiration of food or vomitus

- obstruction of a bronchus (foreign body or neoplasm)

- inhalation of irritant gases

- major surgery

- chronic debilitating diseases, malnutrition

Lobar pneumonia:

S. pneumoniae.

Previously healthy individuals.

Abrupt onset.

Unilateral stabbing chest pain on inspiration (due to fibrinous pleurisy).

Pathology of lobar pneumonia:

4 phases:

Congestion

Lasts < 24 hours: Alveoli filled with

oedema fluid and bacteria.

Red hepatization

• Firm, 'meaty' and airless appearance of lung.

• Alveolar capillary dilatation.

• Strands of fibrin extending from one alveolus to

another via inter-alveolar pores of Kohn.

• Also neutrophils in alveoli.

• Pleura: Fibrinous exudate.

Grey hepatization

Less hyperaemia.

Macrophages, neutrophils + fibrin

Resolution

- Lysis and removal of fibrin via sputum +lymphatics.

- Begins after 8-9 days (without antibiotics).

- Sudden improvement of patient's condition.

Complications of lobar pneumonia

1. Abscess formation

2. Empyema

3. Failure of resolution ⇒ intra-alveolar scarring

('carnification') ⇒ permanent loss of ventilatory

function of affected parts of lung.

4. Bacteraemia:

- Infective endocarditis

- Cerebral abscess / meningitis

- Septic arthritis

Klebsiella pneumoniae

• Common inhabitant of oral cavity (poor

oral hygiene).

• Lobar pneumonia in the elderly, diabetics,

alcoholics (aspiration of saliva).

Community acquired vs. nosocomial infection

Nosocomial infection:

- Often patients in ICU

- ↓ Local resistance to infection in lungs

- Intubation of respiratory tract

- Altered normal flora due to antibiotics

- E.coli, Klebsiella, Proteus, Pseudomonas,

Staph. aureus.

Immune status

Infection by usually non-pathogenic organisms

('opportunistic infection')

- Pneumocystis carinii

- Other fungi

- Cytomegalovirus (CMV)

Fig. A viral pneumonia with interstitial lymphocyticinfiltrates. Note that there is no alveolar exudate. Thus, the patient with this type of pneumonia will probably not have a productive cough.

The most common causes for viral pneumonia are:

• Influenza

• Parainfluenza

• Adenovirus

• Respiratory syncytial virus (RSV)

- appears mostly in children

• Cytomegalovirus

- in immunocompromised hosts.

Fig. RSV accounts for many cases of pneumonia in children under 2 years, and can be a cause for death in infants 1 to 6 months of age or older.

DEFINITION:

Localised area of suppuration and tissue necrosis.

Lung abscess

Fig. Chest X-ray. Abscess. Note air-fluid level

Aetiopathogenesis

• Aspiration of infected oropharyngeal

contents / vomitus.

NB: Poor oral hygiene and sepsis.

Risk of aspiration:

- Loss of consciousness (alcoholic stupor,

anaesthesia, epilepsy).

- Oesophageal pathology (carcinoma, congenital

atresia / fistula).

• Obstruction of bronchus

- carcinoma, foreign body.

• Complication of pneumonia

- virulent organisms esp. Klebsiella, Staph.

• Bronchiectasis.

• Septic embolism (infective endocarditis on

right-sided heart valves) or septisaemia.

• Penetrating trauma e.g. stab wound.

• Direct spread of sepsis from other organs

(e.g. amoebic liver abscess).

Complications

• Rupture into pleural space ⇒ empyema or

broncho-pleural fistula (⇒ pyopneumothorax).

• Rupture into pericardium ⇒ pericarditis.

• Septisaemia ⇒ sepsis in other organs e.g.

osteomyelitis, brain abscess.

• Erosion of blood vessels ⇒ haemoptysis.

• Organisation ⇒ fibrosis.