Nosocomial pneumonia can be classified into various subtypes, the most common of which is aspiration pneumonia (Marik, 2011). Aspiration is defined as the misdirection of oropharyngeal or gastric contents into the larynx and lower respiratory tract. Aspiration pneumonia then results when orogastric secretions colonized with bacteria produce an infectious response in the lungs. Aspiration of sterile contents causes chemical inflammation or aspiration pneumonitis (Marik, 2011).
There are three causes for aspirations that lead to aspiration pneumonia:
Pneumonitis is best defined as acute lung injury following the aspiration of regurgitated gastric contents. This syndrome occurs in patients with a marked disturbance of consciousness, such as drug overdose, seizures, and anesthesia. Drug overdose is a common cause of aspiration pneumonitis, occurring in approximately 10 per cent of patients hospitalized following a drug overdose. The risk of aspiration increases with the degree of unconsciousness (as measured by the Glasgow Coma Scale). Historically, the syndrome most commonly associated with aspiration pneumonitis is Mendelson's syndrome (Marik, 2011).
Aspiration pneumonia occurs when regurgitated gastric contents or oropharyngeal secretions or food are inadvertently directed into the trachea and subsequently into the lungs. As the bacteria and other microorganisms become part of an infiltrate within the lung tissue, the resulting effect is an infection in the lung (Pace & McCullough, 2010). Approximately half of all healthy adults aspirate small amounts of oropharyngeal secretions during sleep. However, if the mechanical, humoral, or cellular mechanisms are impaired or if the aspirated inoculum is large enough, pneumonia may follow. Any condition that increases the volume and/or bacterial burden of oropharyngeal secretions when the host defense mechanism is impaired may lead to aspiration pneumonia (Marik, 2011). Healthy people commonly aspirate small amounts of oral secretions, but normal defense mechanisms usually clear the inoculum without sequelae. Aspiration of larger amounts, or aspiration in a patient with impaired pulmonary defenses, often causes pneumonia and/or abscess. Elderly patients tend to aspirate because of conditions associated with aging that alter the level of consciousness, sedative use, neurologic disorders, weakness and other disorders. Empyema also occasionally complicates aspiration (Sethi, 2014).
Paediatric populations have different causes of dysphagia than in adult populations. These causes include: cerebral palsy; acquired/traumatic brain injury; other neuromuscular disorders; craniofacial malformations; airway malformations; congenital cardiac disease; gastrointestinal disease; ingestional injuries; and preterm birth (Dodrill & Gosa, 2015; Lefton-Greif & Arvedson, 2007).
Aspiration pneumonia represents five per cent to 15 per cent of pneumonias in the hospitalized population (DiBardino, 2015). It has been suggested that dysphagia carries a seven-fold increase risk of aspiration pneumonia and is an independent predictor of mortality (Metheny, 2011).
Critically ill patients have an increased risk for aspirating oropharyngeal secretions and regurgitated gastric contents. For those who are tube-fed, aspiration of gastric contents is of greater concern. While witnessed large-volume aspirations occur occasionally, small-volume clinically silent aspirations are far more common. Because no bedside tests are currently available to detect microaspirations, efforts to prevent or minimize aspiration take on added importance (American Association of Critical-Care Nurses, 2016). Silent aspiration is frequent in the pediatric population (Lefton-Grief et al, 2006).
Aspiration pneumonia generally occurs in elderly, debilitated patients with dysphagia (Marik, 2011). Epidemiological studies have demonstrated that the incidence of pneumonia increases with aging, with the risk being almost six times higher in those over the age of 75, compared to those less than 60 years of age (Marik, 2011).
Aspiration pneumonia is the major cause of death in patients with dysphagia resulting from neurological disorders including cerebrovascular accidents, Parkinson's disease, and dementia (Marik, 2011).
(DiBardino, 2015; Marik, 2011, American Association of Neuroscience Nurses, 2006)
(Weir et al, 2007)
Note: See also Hospital Harm Improvement Resource – B16: Pneumonia
To prevent aspiration pneumonia and aspiration pneumonitis in hospitalized patients by implementing strategies known to reduce the incidence of aspiration pneumonia and pneumonitis.