According to ASA guidelines, how long before adult elective anesthesia should a patient be NPO?

The choice of having patients be NPO (nil per os, or "nothing by mouth") after midnight aligns with the ASA (American Society of Anesthesiologists) guidelines for adult elective anesthesia. This guideline is based on the principle of reducing the risk of aspiration during anesthesia, especially for procedures that require general anesthesia.

Being NPO after midnight provides a defined time frame that helps ensure the patient’s stomach is empty. This timeframe typically means that solid food should be avoided after midnight, which allows sufficient time for gastric emptying and reduces the risk of any retained gastric contents that could potentially lead to aspiration.

In contrast, guidelines specifying shorter durations, such as 2, 4, or 6 hours, are generally applied to specific situations or types of food and liquids. For example, clear liquids may have a different NPO time requirement than solid foods, but the broader and more traditional guideline encourages fasting from midnight for elective surgeries. This helps maintain a standard practice across various institutions and simplifies instructions for patients preparing for surgery.