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.