Nil By Mouth (NBM) is a medical order that prohibits anyone from giving a patient food, drink, or medications by mouth. This is frequently necessary for several hours prior to surgery requiring general anesthesia, for certain medical conditions, and after some types of surgery. To prevent dehydration, hospital staff will frequently administer fluids through an IV. Other medical conditions may warrant NBM orders, especially when a patient has difficulty or an inability to swallow, has had alcohol poisoning, or when gastrointestinal bleeding or blockage is present. Nil by mouth is the preferred British term, while the United States and other parts of the world use the Latin term nil per os, or NPO.
Prior to receiving general anesthesia, doctors will issue a nil by mouth order to make sure the stomach has time to empty its contents. It can take as long as six hours for food and thicker fluids and up to two hours for water and clear fluids to leave the stomach. Due to the danger of missing oral medication doses, many times oral medications will be allowed during the fasting period. Any danger of aspiration appears minimal because small amounts of water necessary to help the patient swallow medication appear to be safe and clear the stomach quickly.
While under general anesthesia, a patient’s swallow and cough reflexes are suppressed. A fasting period before surgery ensures that if vomiting occurs during surgery, no stomach contents will aspirate into the lungs. If stomach contents are aspirated, a patient can choke or develop pneumonia with dangerous or potentially fatal consequences.
Physicians may order a nil by mouth order for up to 24 hours or longer prior to gastrointestinal surgery. This is not only to allow the stomach to empty, but to empty the entire bowel prior to surgery. After gastrointestinal surgery, the order may remain in place for a period of time to allow the bowel time to rest and heal.
After a nil by mouth order has been lifted, patients will sometimes be limited to clear fluids until the bowel has had time to adjust to the work of digestion again. Once fluids are well tolerated, easily digested foods will be introduced in small amounts. This is to prevent and minimize nausea and vomiting that frequently occur after the stomach has been at rest for several days. Sometimes doctors may order anti-nausea drugs if nausea and vomiting are severe.