Nil per os guidelines: what is changing, what is not, and what should?

Preoperative nil per os (NPO) guidelines have been in existence since the recognition of the risk of perioperative aspiration. These guidelines aim at reducing the risk for gastric content aspiration to the lowest possible, to avoid associated morbidity, unplanned hospital and/or an intensive care admission. Thus, such guidelines are not only considered for patients having major surgeries, but more so in those having ambulatory surgery including those performed at non-operating room anesthesia locations. NPO guidelines have always been controversial due to the paucity of data in support of one recommendation versus another and have seen multiple changes and updates by the issuing national anesthesiology societies as new evidence emerges. At the present time, they have become increasingly permissive, such that the ingestion of clear fluids is now encouraged up to two hours before elective surgery. This has added more fuel to the already heated controversies regarding NPO guidelines and contributed to the experienced variability among different local NPO policies adopted by different clinicians. In this article, we attempt to discuss many of these controversies, including the relationship between NPO duration and the risk of aspiration, NPO and the choice of airway device, NPO and operating room efficiency and NPO for procedural sedation.