Fasting before a wisdom tooth extraction, often referred to as Nil Per Os (NPO), is a strict safety protocol instituted by oral surgeons and anesthesiologists. This practice of consuming nothing by mouth for a specified period before the procedure is a non-negotiable directive. The rule exists because the sedation or anesthesia used causes temporary physiological changes that create a severe risk if the stomach contains food or liquid. Adhering to these instructions ensures a safe surgical experience.
Anesthesia and Loss of Protective Reflexes
Wisdom tooth removal typically involves deep sedation or general anesthesia, medications designed to suppress consciousness and pain perception. These powerful drugs temporarily inhibit the body’s involuntary, protective reflexes that defend the airway. The most obvious is the gag reflex, which normally triggers a cough or retching to expel foreign material from the throat.
Anesthesia can also relax the lower esophageal sphincter (LES), a ring of muscle that acts as a valve between the esophagus and the stomach. The LES is normally kept tightly closed to prevent stomach contents from backing up into the throat. Anesthetic agents, particularly certain volatile gases and opioids, can cause this sphincter to relax.
When the LES relaxes and the gag reflex is suppressed, the body loses its two primary defenses against stomach contents moving into the airway. This physiological state creates a direct pathway for material from the stomach to enter the lungs. The stomach must be empty before any procedure requiring deep sedation or general anesthesia.
The Critical Risk of Aspiration Pneumonitis
The danger of having a full stomach under anesthesia is the risk of regurgitation and subsequent pulmonary aspiration. Regurgitation occurs when stomach contents passively flow back up the esophagus and into the throat because the LES is relaxed. Aspiration is the inhalation of this foreign material into the lungs.
Stomach contents are highly acidic, primarily consisting of hydrochloric acid. When this acidic material is aspirated into the lung tissue, it causes a severe chemical burn and inflammatory reaction known as aspiration pneumonitis, sometimes called Mendelson syndrome. This chemical injury can rapidly progress to acute respiratory distress, leading to difficulty breathing and low oxygen levels.
Aspiration pneumonitis is a serious, life-threatening complication that requires immediate, intensive medical intervention and can be fatal. Beyond the chemical burn, the aspirated material can introduce bacteria into the lungs, leading to a secondary infection known as aspiration pneumonia. Fasting serves as a barrier, ensuring that even if regurgitation occurs, the amount of material is minimal, significantly reducing the severity of potential harm.
Practical Fasting Timelines and Exceptions
Standard pre-operative fasting guidelines allow the stomach enough time to empty before the procedure. For solid food, the typical instruction is to stop eating at least eight hours before the scheduled appointment time. This timeframe is based on the average gastric emptying rate for solid foods, ensuring the stomach is clear of bulky material.
The rules for liquids are less restrictive because they empty from the stomach much faster than solids. Patients are advised to stop consuming clear liquids at least two hours before the procedure. A clear liquid is defined as anything you can see through, such as water, clear apple juice, black coffee or plain tea without milk or creamer, and clear sports drinks. Milk and orange juice are not considered clear liquids because they contain particles and fats that delay gastric emptying.
An exception to the NPO rule is often made for necessary prescription medications, which should be taken with only a tiny sip of water. This small amount of water does not pose a significant risk. Patients must always follow the specific, detailed instructions provided by their oral surgeon or the anesthesiologist, as these directives are tailored to the individual procedure and patient health status.