In patients with delayed gastric emptying or in those at risk of regurgitation, preoperative pharmacological control of gastric acidity and volume may decrease morbidity associated with aspiration.

Historically, the critical values of gastric volume and pH at which patients become at increased risk of aspiration and associated morbidity have been arbitrarily defined as pH <2.5 and volume of
>0.4 ml/kg. This is based on unpublished data from a study on Rhesus monkeys (Roberts, 1974). Subsequent research suggests that the acidity of gastric contents may be more relevant than volume (James 1984, Raidoo 1990).