Aspiration pneumonia is a pneumonia that develops as a result of foreign materials gaining entry to the bronchial tree, usually oral or gastric contents such as food and saliva. Depending on the acidity of the aspirate a chemical pneumonitis can develop, as well as bacterial pathogens adding to the inflammation.

Aetiology

Aspiration pneumonia often results from an incompetent swallowing mechanism, such as those that occur in neurological disease or injury such as stroke, multiple sclerosis and intoxication.

Iatrogenic causes, such as intubation, can also result in aspiration pneumonia developing.

Risk factors:

• Poor dental hygiene
• Swallowing difficulties
• Prolonged hospitalization or surgical procedures
• Impaired consciousness
• Impaired mucociliary clearance

The right middle and lower lung lobes are the most common sites affected, due to the larger calibre and more vertical orientation of the right main bronchus.

The bacteria implicated in aspiration pneumonia may be aerobic or anaerobic (anaerobic are most common). Examples of aerobic bacteria include:

• Streptococcus pneumoniae
• Staphylococcus aureus
• Haemophilus influenzae
• Pseudomonas aeruginosa