Aspiration pneumonia

Aspiration pneumonia
Classification and external resources
Histopathologic image of aspiration pneumonia in an elderly patient with debilitating neurologic illness. Note foreign-body giant cell reaction. Autopsy case. H & E stain.
ICD-10	J69.0, P24.9
ICD-9	506.0,507,770.18
MedlinePlus	000121
eMedicine	emerg/464
MeSH	D011015

Aspiration pneumonia is bronchopneumonia that develops due to the entrance of foreign materials into the bronchial tree,^[1] 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) 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.

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.

Implicated bacteria

When bacteria are implicated, they are usually of the aerobic:

• Streptococcus pneumoniae^[2]
• Staphylococcus aureus^[2]
• Haemophilus influenzae^[2]
• Pseudomonas aeruginosa^[2]

They may also be admixed with anaerobic bacteria oral flora:

• Bacteroides^[2]
• Prevotella^[2]
• Fusobacterium^[2]
• Peptostreptococcus^[2]

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.^[3]

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.^[4]

See also

• Dysphagia
• Meconium aspiration syndrome
• Nosocomial pneumonia
• Superior mesenteric artery syndrome

References