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Aspiration Pneumonia – 1 contact hour
Definition
Pneumonia remains the seventh leading cause of death in the United States. As the US population ages, healthcare providers may encounter an increasing number of cases of aspiration pneumonia, both community-acquired and nosocomial infections. Awareness of this disease is important, because diagnosis is usually based on clinical findings and initial therapy is primarily empirical.
Aspiration pneumonia is caused by inhaling foreign material (usually food, liquids, vomit, or secretions from the mouth) into the lungs. This may lead to an inflammatory reaction, a lung infection (pneumonia), or a collection of pus in the lungs (lung abscess). Aspiration pneumonia is also known as anaerobic pneumonia; aspiration of vomitus; necrotizing pneumonia; aspiration pneumonitis or chemical pneumonitis.
Aspiration Pneumonitis
Aspiration pneumonitis represents chemical damage to the tracheobronchial tree. Such materials as mineral oil, hydrocarbons, and gastric acid may cause different patterns of injury. The most common clinical scenario is aspiration of gastric contents. Aspiration of low pH gastric secretions is associated with immediate injury to the tracheobronchial tree and lung parenchyma best likened to a “flash burn”. Bronchoscopy in such cases shows diffuse bronchial erythema. The severity of lung injury is directly related to the pH of the aspirated material and is greatest when the pH is less than 2.5.
Because of the relative sterility of normal gastric contents, bacteria do not play an important role in the early stages of this disease. However, this does not hold true in patients with gastroparesis or small-bowel obstruction, or in those using antacids (PPI, H2-receptor antagonists). Regardless of the bacterial load of the inoculum, bacterial superinfection may occur after the initial chemical injury.
Aspiration Pneumonia
Aspiration pneumonia results from chronic, usually unwitnessed, inhalation of small amounts of oropharyngeal contents, leading to an infectious process. Aspiration pneumonia is defined as the development of an infiltrate in a patient at increased risk of oropharyngeal aspiration. It occurs when a patient inhales material from the oropharynx that is colonized by upper airway flora.
Causative Organisms
Initial bacteriologic studies into the causative organisms of community-acquired aspiration pneumonia indicated the anaerobic species as the predominant pathogens. However, subsequent studies revealed that Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenzae, and Enterobacteriaceae are the most common organisms implicated in community-acquired aspiration pneumonia. Hospital-acquired aspiration pneumonia, on the other hand, is often caused by gram-negative organisms, including Pseudomonas aeruginosa, particularly in intubated patients.
Risk Factors
Aspiration pneumonia most commonly occurs in individuals with chronically impaired airway defense mechanisms. Thus, any condition that reduces a patient’s gag reflex and/or ability to maintain an airway increases the risk of aspiration pneumonia or pneumonitis.
Risk factors for this disease include:
- Decreased level of consciousness (acute and chronic alcohol abuse; drug overdose; stroke; seizure; head trauma; anesthesia, including conscious sedation for upper gastrointestinal endoscopy)
- Isolated alteration of the swallowing reflex associated with pharyngeal disease
- Dysphagia (esophageal cancer, achalasia, tracheobronchial fistula, neurologic disorders)
- Gastroesophageal reflux
- Neurologic disease (stroke, amyotrophic lateral sclerosis, myasthenia gravis, multiple sclerosis, Parkinson’s disease)
- Mechanical and device-related impairment of upper aerodigestive tract (nasogastric and percutaneous feeding tubes, endotracheal tubes, tracheostomy)
- Vomiting
- Bronchial obstruction due to neoplasm or foreign body
- Bronchiectasis
- Pulmonary infarction
Other risk factors include poor dentition and poor oral care, both of which increase the bacterial burden of oropharyngeal secretions. Some studies indicate that aspiration pneumonia is more common in males than in females, and that it is also more prevalent in extremely young or old patients.
