During anesthesia induction, the patient's muscles are in a relaxed state. At this time, if there is food and water in the stomach, it may flow back to the mouth and throat. When the anesthesiologist inhales oxygen under pressure, these things will flow back to the trachea and lungs to cause aspiration, which will be very dangerous and the incidence of postoperative pneumonia will increase. Generally, adults do not drink water for 6 hours, and children do not drink water for 4 hours.