Aspiration Pneumonia Pathophysiology and Mechanisms

Primary Mechanisms of Aspiration

Bacteria can invade the lower respiratory tract through several routes, with aspiration of oropharyngeal organisms being the most important mechanism for both nosocomial and community-acquired pneumonia, according to the Centers for Disease Control and Prevention 1
Other mechanisms include inhalation of aerosols containing bacteria, hematogenous spread from distant body sites, and possibly bacterial translocation from the gastrointestinal tract, as reported by the Centers for Disease Control and Prevention 1, 2
In radioisotope-tracer studies, 45% of healthy adults were found to aspirate during sleep, indicating that aspiration is common even in healthy individuals, as noted by the Centers for Disease Control and Prevention 2

Persons with abnormal swallowing, such as those with depressed consciousness, respiratory tract instrumentation, mechanical ventilation, or gastrointestinal diseases, are particularly likely to aspirate, according to the Centers for Disease Control and Prevention 2
Post-surgical patients, especially those who have undergone recent surgery, have increased risk of aspiration, as reported by the Centers for Disease Control and Prevention 2
Elderly nursing home residents, particularly those with difficulty swallowing food, use of sedative medications, being fed by gastric tube, or requiring total assistance for oral care, are at higher risk, as noted by the American College of Physicians 3
Stroke patients demonstrate aspiration on videofluoroscopic swallow evaluation in 22-38% of cases, according to the American College of Physicians 3

The high incidence of gram-negative bacillary pneumonia in hospitalized patients results from factors that promote colonization of the pharynx by gram-negative bacilli and their subsequent entry into the lower respiratory tract, as reported by the Centers for Disease Control and Prevention 2
Oropharyngeal or tracheobronchial colonization begins with the adherence of microorganisms to the host's epithelial cells, according to the Centers for Disease Control and Prevention 2

The stomach can be an important reservoir of organisms that cause nosocomial pneumonia, as noted by the Centers for Disease Control and Prevention 2
Administration of antacids and H-2 blockers for prevention of stress bleeding in critically ill patients has been associated with gastric bacterial overgrowth, according to the Centers for Disease Control and Prevention 4

Typical presentation includes fever, cough, and auscultatory findings such as rales or evidence of pulmonary consolidation, as reported by the American College of Physicians 3
In neonates and infants, aspiration may present with apnea and increased swallowing frequency rather than coughing, according to the American College of Physicians 3

The American Geriatrics Society recommends that aspiration pneumonia is a bacterial infection of the lung parenchyma caused by aspiration of contaminated oropharyngeal secretions, while chemical pneumonia is a sterile inflammatory injury from aspiration of gastric acid or other toxic substances that typically resolves within 24 hours without antibiotics 5

Chemical pneumonitis results from aspiration of gastric contents causing direct chemical irritation to lung tissue, and symptoms typically resolve within 24 hours without antibiotic therapy, according to the American Geriatrics Society 5
Aspiration of oropharyngeal organisms is the most important mechanism for both nosocomial and community-acquired pneumonia, as stated by the Centers for Disease Control and Prevention 6
The American Geriatrics Society notes that symptoms of aspiration pneumonia persist beyond 24-48 hours and worsen without treatment 5

The American Geriatrics Society recommends that antibiotics are not required for pure chemical pneumonitis, but are mandatory for aspiration pneumonia 5
The Centers for Disease Control and Prevention states that aspiration of oropharyngeal organisms is the most important mechanism for both nosocomial and community-acquired pneumonia, and treatment should be guided by the severity of the infection and the presence of risk factors 6

The American Geriatrics Society suggests that at 24 hours, improving clinically indicates chemical pneumonitis, and continuing supportive care only is recommended, while persistent or worsening symptoms indicate aspiration pneumonia, and initiating antibiotics immediately is necessary 5