When a patient undergoes general anesthesia, or has sedating drugs administered, reflexes may be lost, and the chance of vomiting stomach contents upward, and having these materials enter the windpipe and lungs (aspiration) is significant. Thus, for most operations, whenever circumstances permit (emergency procedures require different considerations), the patient is kept NPO (nihil per os, or nothing by mouth) for at least 6 to 8 hours before the procedure.
This time may vary depending on other problems. Patients who are very obese often have delayed stomach emptying, and a longer time is advisable. If there are problems with the gastrointestinal tract ,as often is the case when undergoing abdominal surgery, delayed gastric emptying may be due to mechanical disease, such as scarring from duodenal ulcers, or due to the intestine not functioning properly due to infection or inflammation.
Anesthesiologists take precautions to minimize the chance of aspiration. Most commonly, the larynx (voice box) is gently pressed posterior to shut off the pharynx while anesthesia is being induced, and that pressure maintained until a cuffed endotracheal tube is safely inserted into the trachea (windpipe) and aspiration prevented. The oral cavity is then typically suctioned, especially when removing the tube; the stomach may well be emptied by a tube when the patient is anesthetized.
For relatively small or “minor” operations being done solely under local anesthesia alone it is not necessary to have an empty stomach, and one can eat and drink normally.
A particularly common question patients ask, and surgeons and anesthesiologists must address, is whether the patient should take his or her usual oral medications prior to surgery. Ideally, these medications should be reviewed during preoperative assessment, and the patient advised which to take and which not. Often additional medications are prescribed to be taken just prior to operation.
Generally speaking, regular oral medications may be taken with a small amount of water necessary to swallow them prior to operation.