Chapter 5

Pulmonary aspiration, an uncommon occurrence in nonemergency airway management, may lead to a spectrum of sequelae, from no discernable effects to significant morbidity and mortality. In this chapter, we will outline the known factors that increase the risks of aspiration and how airway management may be optimized to reduce the risks to the patient.

Although reported in the literature as a relatively uncommon complication of nonemergency airway management, a majority of airway practitioners will acknowledge that the risk of aspiration is a major concern to them in daily practice. Most would acknowledge that if they have not had an episode of aspiration in one of their patients, they know a colleague who has had to deal with the complication. Kluger and Willemsen1 reported in 1998 that over 71% of all anesthesiologists responding to a national mail-in survey in New Zealand had had at least one case of aspiration in their careers.

### 5.2.1 When Was Gastric Aspiration First Described?

Mendelson was the first to describe the occurrence of aspiration in conjunction with the delivery of obstetrical anesthesia.2 Since that time, a plethora of publications have followed, outlining the risks and ways of preventing the problem. Unfortunately, much of the information is conflicting, and conclusions have been derived from studies with surrogate endpoints that may have very little to do with actual clinical risks. For example, the often-quoted study by Roberts and Shirley3 suggested a gastric volume of greater than 25 mL and pH of less than 2.5, as a specific risk factor for aspiration. This postulation was accepted by subsequent investigators who directed their efforts for prevention of aspiration to the assumption that these specific values were critical factors in predicting the outcome of aspiration.

### 5.2.2 What Was Sellick's Approach to Minimize the Risk of Gastric Aspiration?

In the discussion section of his 1961 paper advocating the use of cricoid pressure during the induction of anesthesia to prevent the aspiration of gastric contents, Sellick examined alternatives available at the time.4 He identified inhalational induction in the supine or lateral position (with head-down tilt) and rapid IV induction of anesthesia in the sitting position. He commented that, with inhalational induction, vomiting usually occurred in lighter stages of anesthesia when protective reflexes were hopefully still present and noted that any difficulty during induction predisposed to regurgitation and anoxia. Rapid IV induction in the sitting position often led to cardiovascular collapse in critically ill patients, and pulmonary aspiration was made more likely by the sitting position, if gastric reflux occurred. Sellick advocated the use of cricoid pressure during induction of anesthesia as a third option.

Sellick suggested that the stomach should be emptied before induction and the nasogastric tube then be removed. He was of the opinion that the nasogastric tube would prevent esophageal occlusion with cricoid pressure. The patient was positioned with the head and neck ...

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