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Introduction

Pneumonia—“Captain of the Men of Death”

—William Osler1

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, as well as 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. In addition, a variety of pulmonary conditions have been described from chronic recurrent occult aspiration, most notably “diffuse aspiration bronchiolitis.3 Other aspiration syndromes include airway obstruction, lung abscess, exogenous lipoid pneumonia, chronic interstitial fibrosis, and Mycobacterium fortuitum pneumonia. This chapter will focus on the pathophysiology, clinical features and management of aspiration pneumonitis, aspiration pneumonia, and diffuse aspiration bronchiolitis.

Aspiration Pneumonitis

Aspiration pneumonitis is best defined as acute lung injury following the aspiration of regurgitated gastric contents.2 This syndrome occurs in patients with a marked disturbance of consciousness such as drug overdose, seizures, coma due to acute neurologic insults, massive cerebrovascular accident, following head trauma and during anesthesia. It is important to emphasize that aspiration pneumonitis only occurs in patients who have a depressed level of consciousness with impairment of airway protective reflexes. In clinical practice, drug overdose is the most common cause of aspiration pneumonitis, occurring in approximately 10% of patients hospitalized following a drug overdosage. Adnet and Baud4 demonstrated that the risk of aspiration increases with the degree of impairment in consciousness (as measured by the Glasgow Coma Scale). Historically, the syndrome most commonly associated with aspiration pneumonitis is Mendelson’s syndrome, reported in 1946 in obstetric patients who aspirated while receiving general anesthesia.5 Mendelson’s original report consisted of 44,016 nonfasted obstetric patients whom he studied between 1932 and 1945, of whom more than half received an “operative intervention” with ether by mask without endotracheal intubation. He described aspiration in 66 patients (1:667). Although several of the patients were critically ill from their aspiration, recovery was usually complete within 24 to 36 hours and only two patients died (1:22,008).

Although aspiration is a widely feared complication of general anesthesia, clinically apparent aspiration in modern anesthesia practice is exceptionally rare, and in healthy patients the overall morbidity and mortality are low (see section below). The risk of aspiration is greatly increased in patients intubated emergently in the field, emergency room or in the ICU. In these patients every effort should be made to reduce the risk of aspiration; this includes removing dentures and clearing the airway and in certain ...

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