Aspiration pneumonia

Aspiration pneumonia
Histopathologic image of aspiration pneumonia in an elderly patient with debilitating neurologic illness. Note foreign-body giant cell reaction. Autopsy case. H & E stain.
Classification and external resources
Specialty	pulmonology
ICD-10	J69.0, P24.9
ICD-9-CM	507,770.18 997.32
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), 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 (abbrev. as NPO), i.e. nothing by mouth, for at least four hours before surgery.

Risk factors

• Ethnicity^[2]
  • In the United States African Americans are hospitalized at a significantly higher rate than whites for aspiration pneumonia. Asians have a lower risk of death, and the risk of death for African Americans is not significantly different from whites in this analysis of aspiration pneumonia discharges. Hispanics have a lower risk of death than non-Hispanics.
• 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.^[3][4]
• 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.^[5]

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^[6]
• Staphylococcus aureus^[6]
• Haemophilus influenzae^[6]
• Pseudomonas aeruginosa^[6]

They may also be admixed with anaerobic bacteria oral flora:

• Bacteroides^[6]
• Prevotella^[6]
• Fusobacterium^[6]
• Peptostreptococcus^[6]

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.^[7]

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.^[8]

See also

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

References

1. "aspiration pneumonia" at Dorland's Medical Dictionary
2. Oliver, N.M., Stukenborg, G.J., Wagner, D.P., Harrell, F.E., Kilbirdge, K.L., Lyman, J.A., Einbinder, J., & Connors, A.F. (2004). Ethnicity on In-Hospital Mortality from Aspiration Pneumonia. Journal of the National Medical Association, 96(11), 1462-1469.
3. Scannapieco, F.A., Mylotte, J.M. (1996). Relationship between periodontal disease and bacterial pneumonia. Journal of Periodontal, 67, supple 10, 1114-1122.
4. van der Maarek-Wierink, C.D., Vanobbergen, J.N., Bronkhorst, E.M., Schols, J.M., & de Baat, C., (2011). Risk factors for aspiration pneumonia in frail older people: a systematic literature review. Journal of American Medical Directors Association, 12(5), 344-354.
5. Taylor, G.W., Loesche, W.J., & Terpenning, M.S. (2000). Impact of Oral Diseases on Systemic Health in the Elderly: Diabetes Mellitus and Aspiration Pneumonia. Journal of Public Health Dentistry, 60(4), 313-320
6. Table 13-7 in: Mitchell, Richard Sheppard; Kumar, Vinay; Abbas, Abul K; Fausto, Nelson. Robbins Basic Pathology: With STUDENT CONSULT Online Access. Philadelphia: Saunders. ISBN 1-4160-2973-7. 8th edition.
7. Anand Swaminathan, MD. "eMedicine.com: Pneumonia, Aspiration". Retrieved: 2007-01-20
8. Mukhopadhyay S, Katzenstein AL (2007). "Pulmonary disease due to aspiration of food and other particulate matter: a clinicopathologic study of 59 cases diagnosed on biopsy or resection specimens.". American Journal of Surgical Pathology. 31 (5): 752–759. doi:10.1097/01.pas.0000213418.08009.f9. PMID 17460460.