Aspiration pneumonia is bronchopneumonia that develops due to the entrance of foreign materials into the bronchial tree, usually oral or gastric contents (including food, saliva, or nasal secretions). Depending on the acidity of the aspirate, a chemical pneumonitis can develop, and bacterial pathogens (particularly anaerobic bacteria) may add to the inflammation.
§Causes
Aspiration pneumonia is often caused by an incompetent swallowing mechanism, such as occurs in some forms of neurological disease or injury including multiple sclerosis, CVA (stroke), Alzheimer's disease or intoxication. An iatrogenic cause is during general anaesthesia for an operation and patients are therefore instructed to be nil per os (NPO) (aka Nothing By Mouth) for at least four hours before surgery.
§Risk factors
- Ethnicity
- Age, being male, poor dental hygiene, lung disease, swallowing difficulties, diabetes mellitus, severe dementia, malnutrition, Parkinson’s disease, use of antipsychotic drugs, proton pump inhibitors, and angiotensin-converting enzyme inhibitors.
- Reduced functional status, resident in institutional setting, prolonged hospitalization or surgical procedures, impaired consciousness, chronic swallowing disorders, mechanical airway interventions, immuno-compromised, history of smoking, antibiotic therapy, advanced age, reduced pulmonary clearance, diminished cough reflex, disrupted normal mucosal barrier, impaired mucociliary clearance, alter cellular and humoral immunity, obstruction of the airways, and damaged lung tissue.
Whether aspiration pneumonia represents a true bacterial infection or a chemical inflammatory process remains the subject of significant controversy. Both causes may be present with similar symptoms.
§Implicated bacteria
When bacteria are implicated, they are usually aerobic:
- Streptococcus pneumoniae
- Staphylococcus aureus
- Haemophilus influenzae
- Pseudomonas aeruginosa
They may also be admixed with anaerobic bacteria oral flora:
- Bacteroides
- Prevotella
- Fusobacterium
- Peptostreptococcus
§Location
The location is often gravity dependent, and depends on the patient position. Generally, the right middle and lower lung lobes are the most common sites of infiltrate formation due to the larger caliber and more vertical orientation of the right mainstem bronchus. Patients who aspirate while standing can have bilateral lower lung lobe infiltrates. The right upper lobe is a common area of consolidation in alcoholics who aspirate in the prone position.
§Diagnosis
Aspiration pneumonia is typically diagnosed by a combination of clinical circumstances (debilitated or neurologically impaired patient), radiologic findings (right lower lobe pneumonia) and microbiologic cultures. Some cases of aspiration pneumonia are caused by aspiration of food particles or other particulate substances like pill fragments; these can be diagnosed by pathologists on lung biopsy specimens.
§See also
- Dysphagia
- Meconium aspiration syndrome
- Nosocomial pneumonia
- Superior mesenteric artery syndrome
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