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, acute respiratory distress syndrome, empyema, parapneumonic effusion, and pneumonia. Some include chemical-induced inflammation of the lungs 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.
Signs and symptoms Signs and symptoms of aspiration pneumonia may develop gradually, with increased respiratory rate, foul-smelling sputum, hemoptysis, and fever. Complications may occur, such as exudative pleural effusion, empyema, and lung abscesses. 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.
Causes Most aspiration events occur in patients with 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. The aspiration of oropharyngeal secretions with a high bacterial load, combined with impaired mechanical, humoral, or cellular defense mechanisms, facilitates the entry of bacteria into the lungs and may lead to the development of aspiration pneumonia.
Risk factors 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. While swallowing dysfunction is associated with aspiration pneumonia, dysphagia may not be sufficient unless other risk factors are present. Neurologic conditions that can directly impact the nerves involved in the swallow mechanism include stroke, neurodegenerative diseases (such as 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 sex, 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.
Bacteria Bacteria involved in aspiration pneumonia may be either aerobic or anaerobic. Common aerobic bacteria involved include: 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: BacteroidesTable 13-7 in: Prevotella Fusobacterium Peptostreptococcus
Pathophysiology Aspiration is defined as inhalation of oropharyngeal or gastric contents into the pulmonary tree. Depending on the composition of the aspirate, three complications have been described: Chemical pneumonitis may develop whose severity depends on the pH value and quantity of aspirate. The two lung changes after acid aspiration are: a) direct toxic damage to the respiratory epithelium resulting in interstitial pulmonary edema and b) a few hours later, inflammatory response with production of cytokines, neutrophil infiltration, and macrophage activation. Oxygen-free radicals are generated which, in turn, lead to further lung damage. Patients may remain asymptomatic after acid aspiration. Others may develop dyspnea, pleuritic chest pain, cough, fever, bloody or frothy sputum, and respiratory failure. Aspiration pneumonia may develop. The third complication occurs after inhalation of particulate matter that obstructs airways. The patients will have sudden arterial hypoxemia with development of lung atelectasis.
Location 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.
Diagnosis
Evaluation of aspiration is generally performed with a video fluoroscopic swallowing study involving radiologic evaluation of the swallowing mechanism via challenges with liquid and solid food consistencies. These studies allow for evaluation of penetration to the vocal folds and below but are not a sensitive and specific marker for aspiration. Additionally, it is difficult to distinguish between aspiration pneumonia and aspiration pneumonitis.
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 right 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, 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.
Prevention There have been several practices associated with decreased incidence and decreased severity of aspiration pneumonia as detailed below.
Oral hygiene 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.
Enhanced swallow 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.
After surgery