The instruction to fast before surgery, often termed Nil Per Os (NPO), or “nothing by mouth,” is a standard safety measure before receiving anesthesia. This rule is designed to prevent serious complications that can arise when a patient is unconscious. Following pre-operative instructions precisely ensures the procedure is safe and can proceed on schedule. The common anxiety surrounding these rules often centers on the body’s natural functions, such as the production and swallowing of saliva.
Saliva and the NPO Rule
Swallowing naturally produced saliva is medically safe and does not violate the NPO rule before a surgical procedure. Saliva is an endogenous substance, meaning the body produces it internally. The volume of saliva is insignificant compared to a deliberate intake of liquid or solid food. Patients should not attempt to spit or avoid swallowing their own saliva, as this action is a normal, continuous physiological process. Saliva primarily consists of water, electrolytes, and digestive enzymes, and it passes through the stomach rapidly without posing a risk. The focus of NPO is on external intake that could fill the stomach with a significant volume or complex substances.
The Critical Reason for NPO
The fundamental purpose of the NPO rule is to prevent pulmonary aspiration during general anesthesia. Aspiration occurs when stomach contents, such as food, liquid, or acidic gastric fluid, are regurgitated into the esophagus and then accidentally inhaled into the lungs. This event can lead to severe consequences, including aspiration pneumonitis, respiratory failure, or death. When a patient is under general anesthesia, the protective reflexes that normally prevent choking are suppressed. Anesthetic agents also cause the muscles to relax, including the lower esophageal sphincter. If the stomach contains a significant volume of contents, this relaxation can allow material to easily flow back up and enter the airway. The danger comes from the volume and the highly acidic nature of the stomach contents, which can cause chemical burns and inflammation in the lung tissue.
Strictly Prohibited Items
To maintain a safe, empty stomach, there are clear boundaries for what is prohibited, and these items go beyond just solid food. Clear liquids, such as water, black coffee, or pulp-free juice, are typically allowed up until two hours before the procedure. Even small sips of water within that two-hour window can be a violation of the rule, as the ingestion of any item that delays gastric emptying or stimulates digestive juices is prohibited. Chewing gum, hard candies, and lozenges are problematic because they stimulate the production of stomach acid, increasing the risk of lung injury if aspiration occurs. Smoking or vaping is also prohibited on the day of surgery, as it can increase the volume of respiratory secretions and affect the body’s response to anesthesia.
Accidental Ingestion Protocol
If a patient accidentally violates the NPO rules, such as by drinking a glass of water or chewing gum within the restricted timeframe, they must immediately and honestly inform the surgical team. Hiding the ingestion puts the patient at risk of aspiration during the procedure. The surgical team needs to know the type and quantity of the item consumed, as well as the exact time of ingestion, to accurately assess the risk. Depending on the substance ingested, the time elapsed, and the urgency of the surgery, the anesthesiologist and surgeon will determine the safest course of action. This may involve postponing the surgery to allow for adequate stomach emptying or requiring special precautions during the induction of anesthesia.