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. These conditions enable the entry of bacteria into the lungs, thus allowing the development of an infection. 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 Parkinsons 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 bodys 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.
If there is a large accumulation of fluid within the lungs, drainage of the fluid may also aid in the healing process. Prognosis
Dysphagia clinicians often recommend alteration of dietary regimens, altered head positioning, or removal of all oral intake. While studies have suggested that thickening liquids can decrease aspiration through slowed pharyngeal transit time, they have also demonstrated increased pharyngeal residues with risk for delayed aspiration. The ability of clinical interventions to reduce pneumonia incidence is relatively unknown. Dietary modifications or nothing-by-mouth status also have no effect on a patients ability to handle their own secretions. A patients individual vigor may impact the development of pulmonary infections more than aspiration. Also increased pneumonia risk exists in patients with esophageal dysphagia when compared to stroke patients because patients with stroke will improve as they recover from their acute injury, whereas esophageal dysphagia is likely to worsen with time. In one cohort of aspiration pneumonia patients, overall three-year mortality was 40%.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.