Aspiration pneumonia is a specific form of lung infection (pneumonia) that develops when oral or gastric contents (including food, saliva, or nasal secretions) enter the bronchial tree. Depending on the acidity of the aspirate, a chemical pneumonitis can develop, and bacterial pathogens (particularly anaerobic bacteria) may add to the inflammation.

Causes

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Aspiration pneumonia is often caused by an incompetent swallowing mechanism, such as occurs in some forms of neurological disease (a common cause being strokes) or while a person is intoxicated. An iatrogenic cause is during general anaesthesia for an operation and patients are therefore instructed to be nil per os (NPO) for at least four hours before surgery.

Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy. Both causes may present with similar symptoms.

Location

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The right lower lobe of the lung is the most common location of aspiration pneumonia. This is due to the anatomy of the bronchial tree and gravity: in patients who are upright, the bronchus serving this lobe is oriented almost vertically, leaving it at greatest risk to be the target of aspirated secretions.

See also

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• Meconium aspiration syndrome

Pneumonia