NPO guidelines

NPO stands for "Nil Per Os" - translating to "nothing by mouth."

NPO guidelines are enforced prior to providing anesthesia for surgeries as a method to decrease risk of aspiration. The NIH estimates that anesthesia related aspiration occurs 1 in every 2000-3000 cases; of those cases, 50% of them continue to develop further pulmonary complications such as pneumonitis or aspiration pneumonia. Aspirated-related events can become life-threatening; one study estimates that perioperative aspiration pneumonia carries a 27% mortality rate.

Under general anesthesia, 1. protective airway reflexes such involving the epiglottis and swallowing are impaired, and 2. multiple anesthetic agents can decrease lower esophageal sphincter (LES) tone. To minimize aspiration, current medical protocols rely on patient fasting to minimize gastric content available to aspirate.

NPO guidelines are determined by the carbohydrate, fat, and protein content of the foods consumed. Generally, carbohydrates pass through the stomach most rapidly, while fats remain in the stomach for the longest.

Meal/Food	Hours to wait before starting elective surgery
Heavy Meal (high protein and fat content)	8 hours
Light Meal (toast, crackers, low fat-low protein)	6 hours
Infant Formula	6 hours
Breastmilk	4 hours
Clears (water, black coffee, plain tea, Ensure Clear, Boost Breeze, fruit juice no pulp)	2 hours
Miscellaneous
Gum	Do not delay case, but do not encourage

Notably many medical floors keep to a generalized "NPO at midnight" protocol the night prior to surgery to prevent accidental oral intake which may delay surgical cases the next morning. However, without providing a maintenance fluid via a peripheral IV, these restrictive protocols can lead to relatively volume depletion for patients whose surgeries are scheduled for late afternoon/evening.