The instruction to stop drinking water before wisdom teeth removal, known medically as Nil Per Os (NPO), is a mandatory safety measure tied directly to the use of sedation or general anesthesia. This rule is in place to minimize the risk of pulmonary aspiration, a severe complication that occurs when stomach contents enter the lungs during the period of unconsciousness. Even a small amount of liquid in the stomach can turn a routine procedure into a serious emergency. Following these simple fasting guidelines is the most effective way a patient can contribute to their own safety during the operation.
How Sedation Affects Body Reflexes
The safety concern arises because the medications used for deep sedation or general anesthesia temporarily suppress the body’s involuntary protective mechanisms. Patients typically receive intravenous (IV) sedation, which brings them to a deep state of relaxation, or sometimes general anesthesia, which induces full unconsciousness. These states involve muscle relaxation that affects more than just the surgical area.
The drugs specifically depress the reflexes that normally prevent foreign material from entering the lungs. The gag reflex, which typically triggers a forceful cough or retching response when the throat is irritated, is significantly diminished or eliminated entirely. Similarly, the cough reflex, the body’s last line of defense for clearing the windpipe, is also compromised.
When these reflexes are suppressed, the muscles controlling the upper esophageal sphincter—the valve that closes off the stomach from the throat—also relax. If the stomach contains fluid or food, this relaxation can allow the contents to passively regurgitate up the esophagus and into the back of the throat. Because the protective reflexes are inactive, the material can then easily flow into the trachea and lungs.
Understanding Aspiration and Respiratory Complications
The physiological danger of having material in the stomach while sedated is the risk of pulmonary aspiration, which is the inhalation of stomach contents into the larynx and lower respiratory tract. The stomach contains hydrochloric acid, which is highly irritating to the delicate tissues of the lung. The severity of the resulting injury depends on both the volume and the acidity of the aspirated material.
Aspiration of gastric acid triggers a rapid and severe inflammatory reaction in the lungs known as aspiration pneumonitis. This is essentially a chemical burn that causes acute lung injury and compromises the lung’s ability to exchange oxygen, potentially leading to respiratory distress and requiring emergency intervention. Aspiration pneumonitis can progress into aspiration pneumonia, which is an infection caused by bacteria from the stomach or mouth entering the lungs.
Even clear water, while not acidic, can cause a problem by physically washing away the lung’s natural surfactant, a substance that keeps the air sacs open. Minimizing the stomach’s volume by fasting reduces the amount of material available for potential aspiration. This significantly decreases the risk of severe respiratory complications, as aspiration is a complication with a high mortality rate.
Specific Guidelines for Fasting
The “nothing by mouth” rule, or NPO, defines precisely what a patient can and cannot ingest before the procedure. Standard guidelines specify different timeframes for various substances based on how quickly they leave the stomach. For solid foods and non-clear liquids like milk, the standard fasting period is typically six to eight hours before the scheduled time of the procedure.
Water and other clear liquids, which include plain water, black coffee, apple juice without pulp, and clear sports drinks, are generally safe to consume up to two hours before the induction of anesthesia. These liquids pass through the stomach much faster than solids, meaning the stomach is essentially empty well before the procedure begins. The two-hour window for clear liquids is the absolute limit.
Patients must strictly follow the exact instructions provided by their oral surgeon or anesthesiologist, as individual medical conditions or the planned level of sedation may necessitate a longer fasting period. If necessary prescription medication must be taken the morning of surgery, it is usually permissible with only a tiny sip of water, but this must be explicitly approved by the medical team beforehand. Failure to comply with the specific fasting instructions will lead to the cancellation or postponement of the wisdom tooth removal to ensure patient safety.