Pneumonia is defined as acute inflammation of the lung parenchyma distal to the terminal bronchioles (consisting of the respiratory bronchiole, alveolar ducts, alveolar sacs and alveoli).


1.Inhalation of the microbes present in the air

2.Aspiration of organisms from the nasopharynx or oropharynx.

3.Haematogenous spread from a distant focus of infection.

4.Direct spread from an adjoining site of infection

Normal physiology

The normal lung is free of bacteria because of the presence of a number of lung defense mechanisms at different levels such as nasopharyngeal filtering action, mucociliary action of the lower respiratory airways, the presence of phagocytosing alveolar macrophages and immunoglobulins.

Failure of these defense mechanisms and presence of certain predisposing factors result in pneumonias

  1. Altered consciousness. The oropharyngeal contents may be aspirated in states causing unconsciousness e.g. in coma, cranial trauma, seizures, cerebrovascular accidents, drug overdose, alcoholism etc.
  2. Depressed cough and glottic reflexes. Depression of effective cough may allow aspiration of gastric contents e.g. in old age, pain from trauma or thoracoabdominal surgery, neuromuscular disease, weakness due to malnutrition, kyphoscoliosis, severe obstructive pulmonary diseases, endotracheal intubation and tracheostomy.
  3. Impaired mucociliary transport. The normal protection offered by mucus-covered ciliated epithelium in the airways from the larynx to the terminal bronchioles is impaired or destroyed in many conditions favouring passage of bacteria into the lung parenchyma. These conditions are cigarette smoking, viral respiratory infections, immotile cilia syndrome, inhalation of hot or corrosive gases and old age.
  4. Impaired alveolar macrophage function. Pneumonias may occur when alveolar macrophage function is impaired e.g. by cigarette smoke, hypoxia, starvation, anaemia, pulmonary oedema and viral respiratory infections.
  5. Endobronchial obstruction. The effective clearance mechanism is interfered in endobronchial obstruction from tumour, foreign body, cystic fibrosis and chronic bronchitis

Types of pneumonia

Lobar pneumonia

Bronchopneumonia (Lobular pneumonia)

Communityacquired (CAP)

Health care‚Äďassociated (HCAP)

Ventilatorassociated pneumonia (VAP)


Microorganisms gain access to the lower respiratory tract via microaspiration from the oropharynx (the most common route), inhalation of contaminated droplets, hematogenous spread, or contiguous extension from an infected pleural or mediastinal space

  • Edema: Proteinaceous exudates are present in the alveoli.
  • Red hepatization: Erythrocytes and neutrophils are present in the intraalveolar exudate.
  • Gray hepatization: Neutrophils and fibrin deposition are abundant.
  • Resolution: Macrophages are the dominant cell type.

Clinical Manifestations

  1. Fever
  2. Chills
  3. Sweats
  4. Cough (either nonproductive or productive of mucoid, purulent, or blood-tinged sputum)
  5. Pleuritic chest pain
  6. Dyspnea
  7. Nausea, vomiting
  8. Diarrhea
  9. Fatigue
  10. Headache
  11. Myalgias
  12. Joint pain






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