You should generally avoid eating or drinking anything except sips of water for about 12 hours before any scheduled surgical procedure. Regardless of whether the surgery is scheduled as an outpatient (you go home afterward) or inpatient (you stay in the hospital for at least one night) procedure, the most common way to express this “12 hour rule” is for doctors to say that you shouldn’t eat or drink anything after midnight on the day prior to surgery.
These rules were created to minimize the risks associated with inserting breathing tubes during surgery. For all surgeries that require the patient to be asleep, a breathing tube is placed to help protect the airway during the surgery. Because this can stimulate the gag reflex, it is important that the stomach be empty before inserting the tube. Otherwise, material from the stomach could enter the lungs and lead to potentially dangerous complications. Sips of water are allowed because water is quickly absorbed by the stomach.
Since most medicines also dissolve and absorb quickly, normal prescription medications that can be taken with water are usually allowed on the day of surgery. This includes most high blood pressure medications. In some cases, diuretics should not be taken the day of surgery, but this is rare. Your anesthesiologist or surgeon should advise you about which medications you should avoid on the morning of surgery. If you have any questions or concerns, bring them to the attention of your anesthesiologist, surgeon, or nurse as soon as possible. In many cases, the anesthesiologist will call you the day before the surgery, and you can ask any questions you have during this phone call.
In general, any medications that must be taken with food or milk should not be taken the morning of surgery. Some vitamin supplements and all “bulk” medicines, such as fiber pills or Metamucil, should also be avoided the day of surgery. Your anesthesiologist may allow certain exceptions to this rule, depending on the medicine and the type of surgery, but you will need to speak with him specifically about what they might be. If you forget to ask and he does not mention it in the conversation, you should not take the medications you are unsure of. Bring them with you to the hospital, and ask once you are there.