|Microscopic image of aspiration pneumonia in an elderly person with a neurologic illness. Note foreign-body giant cell reaction.|
|Specialty||Emergency medicine, pulmonology|
|Risk factors||Decreased level of consciousness, problems with swallowing, alcoholism, tube feeding, poor oral health|
|Diagnostic method||Based on presenting history, symptoms, chest X-ray, sputum culture|
|Differential diagnosis||Chemical pneumonitis, tuberculosis|
|Medication||Clindamycin, meropenem, ampicillin/sulbactam, moxifloxacin|
|Frequency||~10% of pneumonia cases requiring hospitalization|
Aspiration pneumonia is a type of lung infection that is due to a relatively large amount of material from the stomach or mouth entering the lungs. Signs and symptoms often include fever and cough of relatively rapid onset. Complications may include lung abscess. Some include chemical pneumonitis as a subtype, which occurs from acidic but non-infectious stomach contents entering the lungs.
Infection can be due to a variety of bacteria. Risk factors include decreased level of consciousness, problems with swallowing, alcoholism, tube feeding, and poor oral health. Diagnosis is typically based on the presenting history, symptoms, chest X-ray, and sputum culture. Differentiating from other types of pneumonia may be difficult.
Treatment is typically with antibiotics such as clindamycin, meropenem, ampicillin/sulbactam, or moxifloxacin. For those with only chemical pneumonitis, antibiotics are not typically required. Among people hospitalized with pneumonia, about 10% are due to aspiration. It occurs more often in older people, especially those in nursing homes. Both sexes are equally affected.
Aspiration pneumonia is often caused by a defective swallowing mechanism, such as a neurological disease or as the result of an injury that directly impairs swallowing or interferes with consciousness. Impaired consciousness can be intentional, such as the use of general anesthesia for surgery. For many types of surgical operations, people preparing for surgery are therefore instructed to take nothing by mouth (nil per os, abbreviated as NPO) for at least four hours before surgery. These conditions enable the entry of bacteria into the lungs, thus allowing the development of an infection.
- Impaired swallowing: Conditions that cause dysphagia worsen the ability of people to swallow, causing an increased risk of entry of particles from the stomach or mouth into the airways. Neurologic conditions that can directly impact the nerves involved in the swallow mechanism include stroke, Parkinson's disease, and multiple sclerosis. Anatomical changes in the chest can also disrupt the swallow mechanism. For example, patients with advanced COPD tend to develop enlarged lungs, resulting in compression of the esophagus and thus regurgitation.
- Altered mental status: Changes in levels of consciousness affect the swallow mechanism by both disabling the body's natural protective measures against aspiration as well as possibly causing nausea and vomiting. Altered mental status can be caused by medical conditions such as seizures. However, many other agents can be responsible as well, including general anesthesia and alcohol.
- Bacterial colonization: Poor oral hygiene can result in colonization of the mouth with excessive amounts of bacteria, which is linked to increased incidence of aspiration pneumonia.
- Ethnicity: Asians diagnosed with aspiration pneumonia have a lower risk of death compared to other ethnic groups while African Americans and whites share a relatively similar risk of death. Hispanics have a lower risk of death than non-Hispanics.
- Others: Age, male gender, diabetes mellitus, malnutrition, use of antipsychotic drugs, proton pump inhibitors, and angiotensin-converting enzyme inhibitors. Residence in an institutional setting, prolonged hospitalization or surgical procedures, gastric tube feeding, mechanical airway interventions, immunocompromised, 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.
- Streptococcus pneumoniae
- Staphylococcus aureus
- Haemophilus influenzae
- Pseudomonas aeruginosa
- Klebsiella: often seen in aspiration lobar pneumonia in alcoholics
Anaerobic bacteria also play a key role in the pathogenesis of aspiration pneumonia. They make up the majority of normal oral flora and the presence of putrid fluid in the lungs is highly suggestive of aspiration pneumonia secondary to an anaerobic organism. While it is difficult to confirm the presence of anaerobes through cultures, the treatment of aspiration pneumonia typically includes anaerobic coverage regardless. Potential anaerobic bacteria are as follows:
The location is often gravity dependent, and depends on the person's position. Generally, the right middle and lower lung lobes are the most common sites affected, due to the larger caliber and more vertical orientation of the right mainstem bronchus. People who aspirate while standing can have bilateral lower lung lobe infiltrates. The right upper lobe is a common area of consolidation, where liquids accumulate in a particular region of the lung, in alcoholics who aspirate in the supine position.
Aspiration pneumonia is typically diagnosed by a combination of clinical circumstances (people with risk factors for aspiration) and radiologic findings (an infiltrate in the proper location). A chest x-ray is typically performed in cases where any pneumonia is suspected, including aspiration pneumonia. Findings on chest x-ray supportive of aspiration pneumonia include localized consolidation depending on the patient's position when the aspiration occurred. For example, people that are supine when they aspirate often develop consolidation in the left lower lobe of the lung. Sputum cultures are not used for diagnosing aspiration pneumonia because of the high risk of contamination. Clinical symptoms may also increase suspicion of aspiration pneumonia, including new difficulty breathing and fever after an aspiration event. Likewise, physical exam findings such as altered breath sounds heard in the affected lung fields may also be suggestive of aspiration pneumonia. 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.
While aspiration pneumonia and chemical pneumonitis may appear similar, it is important to differentiate between the two due to major differences in management of these conditions. Chemical pneumonitis is caused by damage to the inner layer of lung tissue, which triggers an influx of fluid. The inflammation caused by this reaction can rapidly cause similar findings seen in aspiration pneumonia, such as an elevated WBC (white blood cell) count, radiologic findings, and fever.  However, it is important to note that the findings of chemical pneumonitis are triggered by inflammation not caused by infection, as seen in aspiration pneumonia. Inflammation is the body's immune response to any perceived threat to the body. Thus, treatment of chemical pneumonitis typically involves removal of the inflammatory fluid and supportive measures, notably excluding antibiotics. The use of antimicrobials is reserved for chemical pneumonitis complicated by secondary bacterial infection.
There have been several practices associated with decreased incidence and decreased severity of aspiration pneumonia as detailed below.
Studies showed that the net reduction of oral bacteria was associated with a decrease in both incidence of aspiration pneumonia as well as mortality from aspiration pneumonia. One broad method of decreasing the number of bacteria in the mouth involves the use of antimicrobials, ranging from topical antibiotics to intravenous antibiotic use. Whereas the use of antibiotics focuses on destroying and hindering the growth of bacteria, mechanical removal of oral bacteria by a dental professional also plays a key role in reducing the bacterial burden. By reducing the amount of bacteria in the mouth, the likelihood of infection when aspiration occurs is reduced as well. For people who are critically ill that require a feeding tube, there is evidence suggesting that the risk of aspiration pneumonia may be reduced by inserting the feeding tube into the duodenum or the jejunum (post-pyloric feeding), when compared to inserting the feeding tube into the stomach (gastric feeding).
Many people at risk for aspiration pneumonia have an impaired swallowing mechanism, which may increase the chance of aspiration of food particles with meals. There is some evidence to indicate that training of various parts of the body involved in the act of swallowing, including the tongue and lips, may reduce episodes of aspiration and aspiration pneumonia, however further research is required to confirm this benefit. Other simple actions during feeding can improve the swallowing capability of a person and thus reduce the risk of aspiration, including changes in position and feeding assistance.
Many instances of aspiration occur during surgical operations, especially during anesthesia induction. The administration of anesthesia causes suppression of protective reflexes, most importantly the gag reflex. As a result stomach particles can easily enter the lungs. Certain risk factors predispose individuals to aspiration, especially conditions causing dysfunction of the upper gastrointestinal system. Identifying these conditions before the operation begins is essential for proper preparation during the procedure. It is recommended that patients fast prior to procedures as well. Other practices that may be beneficial but have not been well-studied include medication that reduce the acidity of gastric contents and rapid sequence induction.
The main treatment of aspiration pneumonia revolves around the use of antibiotics to remove the bacteria causing the infection. Broad antibiotic coverage is required to account for the diverse types of bacteria possibly causing the infection. Currently recommended antibiotics include clindamycin, meropenem, ertapenem, ampicillin/sulbactam, and moxifloxacin. If there is a large accumulation of fluid within the lungs, drainage of the fluid may also aid in the healing process.
Studies have shown that aspiration pneumonia has been associated with an overall increased in-hospital mortality as compared with other forms of pneumonia. Further studies investigating differing time spans including 30-day mortality, 90-day mortality, and 1-year mortality. Individuals diagnosed with aspiration pneumonia were also at increased risk of developing future episodes of pneumonia. In fact, these individuals were also found to be at higher risk for readmission after being discharged from the hospital. Lastly, one study found that individuals diagnosed with aspiration pneumonia were more likely to fail treatment compared to other types of pneumonia.
If left untreated, aspiration pneumonia can progress to form a lung abscess. Another possible complication is an empyema, in which pus collects inside the lungs. If continual aspiration occurs, the chronic inflammation can cause compensatory thickening of the insides of the lungs, resulting in bronchiectasis.
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