Aspiration
Aspiration of gastric contents is a
rare, potentially fatal, and often litigious event that can complicate
anesthesia. Based on an animal study, it is often stated that aspiration of 25
mL of volume at a pH of less than 2.5 will be sufficient to produce aspiration
pneumo-nia. Many factors place patients at risk for aspiration, including
“full” stomach, intestinal obstruction, hiatal hernia, obesity, pregnancy,
reflux disease, emergency surgery, and inadequate depth of anesthesia.
Many approaches are employed to reduce
the potential for aspiration perioperatively. Many of these interventions, such
as the holding of cricoid pressure (Sellick’s maneuver) and rapid sequence
induction, may only offer limited protection. Cricoid pressure can be applied
incorrectly and fail to occlude the esophagus. Whether it has any beneficial effect on outcomes even
when it is applied correctly remains unproven. Anesthetic agents can decrease
lower esophageal sphincter tone and decrease or obliterate the gag reflex,
theoretically increasing the risk for pas-sive aspiration. Additionally,
inadequately anesthe-tized patients can vomit with an unprotected airway,
likewise leading to aspiration. Different combinations of premedications have
been advocated to reduce gas-tric volume, increase gastric pH, or augment lower
esophageal sphincter tone. These agents include anti-histamines, antacids, and
metoclopramide.
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