It is important to NPO, or fast before a surgery, in order to prevent the risk of choking while in surgery. NPO stands for a Latin term, "nil per os," which means nothing by mouth.
During surgery and the anesthesia process, there is the chance that a person could inhale and move stomach contents into their lungs. This could result in choking and even death.
The number of hours that one must fast prior to surgery depends on age and type of food. Adults, for example, should not eat a normal meal within 8 hours of surgery. They should not drink clear liquids for 2 hours leading up to the surgery.