Nil per os
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Nil per os (alternatively nihil/non/nulla per os) (npo or NPO) is a medical instruction meaning to withhold oral food and fluids from a patient for various reasons. It is a Latin phrase whose usual English expansion is nothing by mouth (most literally, "nothing through the mouth"). Variants include nil by mouth (NBM).
Typical reason for NPO instructions are the prevention of aspiration pneumonia, e.g. in those who will undergo general anesthetic, or those with weak swallowing musculature, or in case of gastrointestinal bleeding, gastrointestinal blockage, or acute pancreatitis. Alcohol overdoses that result in vomiting or severe external bleeding also warrants NPO instructions for a period. Pre-surgery NPO orders are typically between 6 and 12 hours prior to surgery, through recovery suite discharge, but may be longer if long acting medications or oral post-meds were administered. It is not uncommon for the food NPO period to be longer than that for liquid, as the American Board of Anesthesiology advises against liquid NPO periods greater than eight hours. The NPO periods for illness tend to be much longer, although exceptions are made for small scheduled amounts of water consumption if an IV drip is not in use. With sufficient IV fluids, NPO periods of several days have been utilized successfully in non-diabetic patients (although short NPO periods in diabetics are possible with IV fluids, insulin, and dextrose (see below). Extended periods (greater than 12 hours) are still contraindicated.
When NPO is needed because of an illness or in preparation of a procedure, insulin drip offers the best control for patients with diabetes mellitus. In such a case, the insulin dose would be determined by initially providing 1 g of insulin for every 5 g of dextrose, administered through intravenous fluids.
"Pseudo-NPO" orders are often utilized after gastrointestinal and/or dental surgeries, in which the patient is limited to a soft-food diet or given a list of foods/types of food to specifically avoid (I.E. grapefruit and grapefruit juice prior to and following surgery).
NPO is one of the abbreviations that is not used in AMA style; "nothing by mouth" is spelled out instead.