<P> Preoperative fasting is the practice of a patient abstaining from oral food and fluid intake for a time before an operation is performed . This is intended to prevent pulmonary aspiration of stomach contents during general anesthesia . </P> <P> The main reason for preoperative fasting is to prevent pulmonary aspiration of stomach contents while under the effects of general anesthesia . Aspiration of as little as 30--40 mL can be a significant cause of suffering and death during an operation and therefore fasting is performed to reduce the volume of stomach contents as much as possible . Several factors can predispose to aspiration of stomach contents including inadequate anesthesia, pregnancy, obesity, difficult airways, emergency surgery (since fasting time is reduced), full stomach and altered gastrointestinal mobility . Increased fasting times leads to decreased injury if aspiration occurs . </P>

Why do you have to be nil by mouth before surgery