The requirement to abstain from food and drink before a procedure, known as nil per os (NPO), is a standard safety measure for patients preparing for surgery. This practice protects the patient while under sedation or general anesthesia. While NPO covers all ingestible items, many patients wonder why seemingly harmless items like chewing gum are included in this strict mandate. Although gum is not typically swallowed, the act of chewing triggers a physiological response that undermines the goal of having an empty stomach before a procedure.
The Risk of Aspiration During Anesthesia
The primary danger the NPO rule prevents is pulmonary aspiration, which occurs when stomach contents enter the lungs. Anesthesia and deep sedation suppress the body’s protective airway reflexes, such as the cough and gag reflexes.
Anesthetic agents also reduce the tone of the lower esophageal sphincter (LES), the muscular valve separating the esophagus from the stomach. A relaxed LES makes it easier for gastric contents to passively regurgitate up the esophagus and into the back of the throat. If this material is inhaled, it can lead to serious complications, including airway obstruction or a severe inflammation of the lung tissue known as chemical pneumonitis.
The severity of an aspiration event is directly related to the volume and the acidity of the material inhaled. A stomach that contains a large volume of highly acidic fluid poses a greater threat to the delicate lung tissues. Therefore, the fasting protocol ensures the stomach is as empty as possible before general anesthesia to minimize the potential for regurgitation and reduce the harm if aspiration were to occur.
Gastric Fluid Stimulation Caused By Chewing
The act of chewing gum interferes with the goal of an empty stomach by stimulating the body’s digestive process. This response is governed by the “cephalic phase” of digestion, which begins before any food actually reaches the stomach. The cephalic phase is a reflex triggered by sensory input, such as the sight, smell, thought, or the physical action of chewing.
The physical movement of chewing sends signals via the vagus nerve to the stomach, preparing the digestive tract for incoming food. This nervous signal prompts the stomach lining to begin producing and secreting gastric fluids, primarily hydrochloric acid. Studies have demonstrated that chewing gum can be as effective as actual food in stimulating this early phase of gastric secretion.
Although the gum itself is not swallowed, the stomach fills with these newly secreted, highly acidic fluids. This increased volume and acidity of gastric contents elevates the risk profile for the patient under anesthesia. If the lower esophageal sphincter relaxes and regurgitation happens, the resulting aspirate will be more corrosive and voluminous due to the fluids stimulated by the chewing. For this reason, anything that causes this physiological response, including hard candies or mints, is forbidden before surgery.
Understanding Pre-Operative Fasting Timelines
Specific pre-operative fasting rules are established by organizations like the American Society of Anesthesiologists (ASA) to balance patient comfort with safety. For healthy adult patients undergoing elective procedures, the guidelines specify different timeframes for various types of ingestion.
Clear liquids, which include water, black coffee, plain tea, and juice without pulp, are generally safe to consume up to two hours before the procedure. Requirements are stricter for non-clear liquids and solid food, which take much longer to empty from the stomach. Patients are instructed to fast from solids for at least six to eight hours before the scheduled time of surgery. Fatty or fried foods can significantly prolong gastric emptying, often requiring a full eight-hour fast.
Adherence to these timeframes is paramount, as failure to follow the instructions can lead to a significant delay or even the cancellation of the surgical procedure. If a patient inadvertently breaks the NPO rule, they must immediately inform the medical staff. While recent guidelines suggest that chewing gum may not necessitate a procedure delay, it is still prohibited, and the staff must confirm it is removed before any sedative is administered.