NPO means nothing by mouth. This must be clarified though because it could mean nothing at all by mouth or ok to have pills, but no food. Often times it is before surgery or a test.
NPO is an acronym for non per os (Latin) or nothing by mouth. This means the patient should receive absolutely nothing by mouth, no food or drink. There are many reasons and circumstances that warrant a physician's order of NPO. Say for example, someone has nausea, vomiting, and diarrhea. The gut needs rest until the offending cause is eliminated by the body. The last thing this person needs is to try to eat, most people that are nauseated get further nauseated if they try to eat.
Another example of when NPO is appropriate is preoperatively. If a person is going to receive general anesthesia, the gut should be empty to try to prevent aspiration of stomach contents postoperatively. Anesthetics very commonly cause nausea and vomiting in a high percentage of people, not to mention the emotional component to having surgery. Some people will vomit after surgery because of the emotional stress of the situation.
NPO stands for Nothing Per Orem which means nothing by mouth. Doctors use this on orders when they do not want the patient to take in any type of food or liquid by mouth.Usually it's ordered for a patient pending a procedure that requires you to have a clean gut (major surgeries, endoscopy, ultrasound of liver), or if you have some gut problem (infection, bleeding).
Nothing by mouth (ie nothing to eat or drink)