“Captain of the Men of Death”
—William Osler’s reference to pneumonia1
Aspiration is defined as the misdirection of oropharyngeal or gastric contents into the larynx and lower respiratory tract.2 An assortment of pulmonary syndromes may occur following aspiration depending on the quantity and nature of the aspirated material, the chronicity of aspiration, and the nature of the host’s defense mechanisms and the host’s response to the aspirated material. The most important syndromes include “aspiration pneumonitis” or Mendelson’s syndrome, which is a chemical pneumonitis caused by the aspiration of gastric contents, and “aspiration pneumonia,” an infectious process caused by the aspiration of oropharyngeal secretions colonized by pathogenic bacteria.2 While there is some overlap between these two syndromes, they are distinct clinical entities.2 The distinction between these two syndromes is based largely on clinical criteria (Table 69-1). Although gastric biomarkers for aspiration are increasingly available (e.g., pepsin, amylase, lipid-laden macrophages), none has been clinically validated.3–5 Serum procalcitonin and other inflammatory markers are unable to distinguish aspiration pneumonitis from aspiration pneumonia.6 The administration of antibiotics is central to the management of aspiration pneumonia, while the treatment of aspiration pneumonitis is largely supportive.2 In addition to aspiration pneumonitis and aspiration pneumonia, a variety of pulmonary conditions result from chronic recurrent occult aspiration, most notably “diffuse aspiration bronchiolitis.”7 Other aspiration syndromes include airway obstruction, lung abscess, exogenous lipoid pneumonia, chronic interstitial fibrosis, and Mycobacterium fortuitum pneumonia. This chapter focuses on the pathophysiology, clinical features, and management of aspiration pneumonitis, aspiration pneumonia, and diffuse aspiration bronchiolitis.
TABLE 69-1Contrasting Features of Aspiration Pneumonitis and Aspiration Pneumonia ||Download (.pdf) TABLE 69-1 Contrasting Features of Aspiration Pneumonitis and Aspiration Pneumonia
|Feature ||Aspiration Pneumonitis ||Aspiration Pneumonia |
|Mechanism ||Aspiration of sterile gastric contents ||Aspiration of colonized oropharyngeal material |
|Pathophysiologic process ||Acute lung injury from acidic and particulate matter ||Acute pulmonary inflammatory response to bacteria and bacterial products |
|Bacteriologic findings ||Initially sterile, with subsequent bacterial infection possible ||Gram-negative rods, gram-positive cocci, and rarely anaerobic bacteria |
|Major predisposing factors ||Depressed level of consciousness ||Dysphagia and gastric dysmotility |
|Age group affected ||Any age group, but usually young persons ||Usually elderly persons |
|Aspiration event ||May be witnessed ||Usually not witnessed |
|Typical presentation ||Patient with a history of depressed level of consciousness in whom a pulmonary infiltrate and respiratory symptom develop ||Institutionalized patient who presents with features of a “community-acquired pneumonia” with an infiltrate in a dependent bronchopulmonary segment |
|Clinical features ||No symptoms or symptoms ranging from a nonproductive cough to tachypnea, bronchospasm, bloody or frothy sputum, and respiratory distress 2 to 5 h after aspiration ||Tachypnea, cough, fever, and signs of pneumonia |
Aspiration pneumonitis is best defined as acute lung injury ...