Pathophysiology

Risk factors for aspiration among emergency patients includes transient or permanent altered mental states with depressed glottic reflexes, anomalies of the esophagus, alcohol or illicit drug intoxication, seizure, tube feedings, anesthesia, advanced age, and supine position. It is not uncommon to see more than one of these risk factors in a single patient. For example, an elderly nursing home patient in a persistent vegetative state with a gastrostomy tube arrives for evaluation of fever. Caretakers may not appreciate aspiration, since the event may be occult secondary to the lack of gag or cough reflex at the time of aspiration.

The severity of the symptoms is related to the volume of material aspirated, the amount of bacterial contamination, and the pH of the material aspirated. Liquids with a pH lower than 2.0 are associated with a much higher mortality rate than are liquids with a higher pH. Aspirated bacteria usually come from oropharyngeal contents, with anaerobic bacteria predominating. Patients in hospitals or long-term care facilities may become colonized by gram-negative bacilli, and these bacteria may make their way into the aspirated inoculum.

Normal mechanisms that protect the airway include the sneeze, gag, and cough reflexes. Particles deposited in the distal nasal epithelium are removed by a sneeze. Lower airways are protected by mucus produced by cells that line the airways. This mucus traps airborne particles of 10-^m diameter. once trapped by the mucous coating, these larger particles are swept proximally by the mucocillary escalator to the oropharynx, where they are expectorated or swallowed. Alveolar macrophages, polymorphonuclear leukocytes, or lymphocytes destroy infectious particles that are small enough to reach the alveoli.

Many of the symptoms of aspiration pneumonia are elicited by the body's inflammatory response to the infectious or irritative material. Proinflammatory cytokines, which increase capillary permeability and are cytotactic, cause migration of fluids and inflammatory cells into the area of irritation. 7 The inflammatory response is responsible for the symptoms of fever, productive cough, and radiographic findings. These findings may not be present when aspiration occurs in an immunocompromised patient who may not be able to mount the inflammatory responses.

Solid material, such as sand, dirt, toys, and other small objects, can cause rapid asphyxiation secondary to mechanical blockage of the trachea. Patients with total or near-total obstruction of the glottis or trachea will be unable to cough or call for help because of the lack of air movement.

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