The preparation for any surgery requiring general anesthesia includes a strict fasting period, often summarized by the Latin phrase Nil Per Os (NPO), meaning “nothing by mouth.” This rule exists to protect the patient from a rare but serious complication, and chewing gum directly violates this safety protocol. Even though the gum is not swallowed, the act of chewing signals the digestive system to prepare for a meal. Maintaining this absolute restriction on oral intake is a foundational step for patient safety before any anesthetic procedure.
How Chewing Increases Gastric Volume
Chewing gum triggers the first stage of digestion, known as the cephalic phase. This phase is governed by the vagus nerve, which connects the brain to the stomach and stimulates digestive activity. Seeing, smelling, or even thinking about food causes the brain to preemptively signal the stomach to begin preparing for a meal.
The physical action of chewing reinforces this neurological signal, causing a significant increase in the production of saliva and, more importantly, gastric secretions. This reflex action leads to a measurable increase in the volume of fluid inside the stomach. Some studies have shown that patients who chew gum before a procedure can have over twice the volume of fluid in their stomach compared to those who follow fasting guidelines precisely.
This increased fluid volume is primarily composed of saliva and gastric acid. While chewing gum does not always significantly alter the acidity level of the stomach contents, it does increase the total amount of fluid present. This excess, acidic fluid creates a larger reservoir of material that can potentially be regurgitated during anesthesia.
Anesthesia and Loss of Airway Protection
General anesthesia fundamentally alters the body’s protective reflexes. Anesthetic agents, such as volatile gases and intravenous sedatives, cause muscle relaxation throughout the body, including the muscles that normally guard the airway. These drugs temporarily suppress the body’s natural defense mechanisms.
Specifically, general anesthesia weakens the muscle tone of the lower esophageal sphincter, the muscle that acts as a valve between the esophagus and the stomach. When this sphincter relaxes, the stomach’s contents can easily move backward into the esophagus and throat. Furthermore, the gag reflex, which normally clears the airway, is completely suppressed by the anesthetic medications.
The combination of a relaxed esophageal valve and a suppressed gag reflex means there is no mechanical or neurological defense against regurgitation. If gastric fluid moves up the esophagus and reaches the back of the throat, there is nothing to stop it from entering the unprotected lungs. This loss of airway protection is a temporary state, but it is the precise period during which the patient is most vulnerable.
The Risk of Aspiration and Delayed Surgery
The combination of increased gastric fluid volume from chewing and the loss of protective reflexes under anesthesia creates the risk of pulmonary aspiration. Aspiration occurs when stomach contents, including acidic fluid and any undigested particles, are accidentally inhaled into the lungs. This event can trigger a severe inflammatory reaction known as aspiration pneumonitis.
If the aspirated material is acidic, it can cause extensive chemical burns to the delicate lung tissues. This can rapidly progress to aspiration pneumonia, a life-threatening complication. The goal of the strict NPO rule is to ensure the stomach is as empty as possible, reducing both the volume and the acidity of any material that could potentially be aspirated.
If a patient admits to or is found to have chewed gum before their procedure, the surgery will often be canceled or delayed. The surgical team must wait until the stomach has emptied the excess fluid produced by the cephalic reflex. Delaying the procedure is a necessary safety measure, ensuring the patient’s stomach is adequately prepared before the anesthetic is administered.