Clinical Pearls & Morning Reports
Large-volume aspiration (macroaspiration) of colonized oropharyngeal or upper gastrointestinal contents is the sine qua non of aspiration pneumonia. Read the NEJM Review Article here.
Q: What are some of the clinical scenarios associated with aspiration pneumonia?
A: Aspiration is often the result of impaired swallowing, which allows oral or gastric contents, or both, to enter the lung, especially in patients who also have an ineffective cough reflex. Large-volume aspiration occurs with dysphagia; head, neck, and esophageal cancer; esophageal stricture and motility disorders; chronic obstructive pulmonary disease; and seizures. Additional risks include degenerative neurologic diseases and impaired consciousness. An important clinical context for aspiration pneumonia is cardiac arrest. The presumed mechanism is aspiration of gastric contents during resuscitation (promoted by stomach ventilation and the resuscitation procedure) and inhalation of oral secretions during bag–valve–mask ventilation and intubation.
Q: Are anaerobes the predominant pathogens in cases of aspiration pneumonia?
A: In the 1970s, anaerobes with or without aerobes were the predominant pathogens in aspiration pneumonia. More recently, there has been a shift to bacteria usually associated with community- and hospital-acquired pneumonias, and anaerobes are recovered less frequently. Studies of the elderly continue to show the trend away from anaerobes. It is unclear why the pathogens have changed, but it may be due to a shift in the demographic characteristics of patients and earlier sampling today than in the past. Prior studies often collected cultures later in the illness, often after the development of empyema or lung abscess.
A: Aspiration pneumonia is usually acute, with symptoms developing within hours to a few days after a sentinel event, although anaerobic aspiration may be subacute because of the less virulent bacteria, and clinical features are difficult to distinguish from those of other bacterial pneumonias. Aspiration pneumonia is associated with higher mortality than other forms of pneumonia acquired in the community (29.4% vs. 11.6%). The diagnosis of aspiration pneumonia depends on a characteristic clinical history (witnessed macroaspiration), risk factors, and compatible findings on chest radiography. These radiographic findings include infiltrates in gravity-dependent lung segments (superior lower-lobe or posterior upper-lobe segments, if the patient is in a supine position during the event, or basal segments of the lower lobe, if the patient is upright during the event).
A: Although the diagnosis is usually clinical, some studies have used quantitative lung-lavage cultures to distinguish bacterial from noninfectious (chemical and bland-aspiration) pneumonitis. Several investigations have studied biomarker and biochemical measurements to predict bacterial infection after aspiration. A study involving 65 intubated patients with risk factors for aspiration and a new lung infiltrate correlated quantitative bronchoalveolar-lavage cultures with serum procalcitonin levels. Measurement of procalcitonin levels on days 1 and 3 did not distinguish the 32 patients with culture-positive aspiration pneumonia from the 33 with culture-negative pneumonitis. In studies of ventilated patients, alpha-amylase levels (from salivary and pancreatic sources) were elevated in airway secretions, at a frequency reflecting the number of risk factors for aspiration, but the relevance of these findings to aspiration pneumonia and chemical pneumonitis is not certain, and this is not a method of value for diagnosis.