The medical term NPO stands for "nil per os," which is a Latin term that means "nothing by mouth," according to the University of Michigan medical school. As there is a risk of the patient aspirating food and fluids into his or her lungs during surgery, anesthesiologists ask that no food or drink is consumed around 2 to 8 hours before surgery begins.
Whether patient needs a local or general anesthetic, there is a risk that their stomach contents will enter the lungs. A patient who experiences aspiration during surgery is at increased risk of pneumonia and pneumotitis. As the stomach's contents are acidic and the lungs are not equipped to handle this acidity, lungs can be damaged as a result of aspiration.
How soon a patient must stop eating and drinking before surgery depends on his or her age and the type of food. Adults must avoid eating normal meals within 8 hours of surgery, light meals within 6 hours and clear liquids within 2 hours. Children should stop eating meals and infant formula 6 hours before surgery, breast milk 4 hours before and clear liquids 2 hours before. These guidelines apply to healthy patients only. They may differ for patients with various health conditions, as well as women in labor.