Patients undergoing medical procedures requiring anesthesia are instructed to refrain from eating or drinking beforehand. This instruction, known as “nil per os” (NPO) or “nothing by mouth,” is a standard safety measure. Its primary purpose is to ensure patient safety and prevent complications during and after the procedure.
Understanding the Main Risk
The main danger of consuming liquids or food before anesthesia is pulmonary aspiration. This occurs when stomach contents are regurgitated and inhaled into the lungs. During anesthesia, the body’s natural protective reflexes that prevent choking are suppressed, making it easier for stomach contents to enter the respiratory tract.
Aspiration can lead to serious complications such as chemical pneumonitis, aspiration pneumonia, and acute respiratory distress syndrome (ARDS). Chemical pneumonitis results from the irritation of lung tissue by acidic stomach contents, leading to inflammation. Aspiration pneumonia involves an infection in the lungs caused by inhaled bacteria from the stomach or mouth. These conditions can cause significant lung damage, respiratory failure, and in severe cases, can be life-threatening.
Anesthesia’s Impact on the Body
General anesthesia induces unconsciousness and relaxes muscles throughout the body. This includes muscles protecting the airway, such as the esophageal sphincters. The lower esophageal sphincter, a barrier between the esophagus and stomach, can experience decreased tone under anesthesia. This allows stomach contents to move back up into the esophagus and throat.
Anesthesia also suppresses protective reflexes like gagging and swallowing, which prevent foreign material from entering the lungs. Without these reflexes, the body is less able to clear regurgitated material from the airway. Additionally, anesthetic agents can slow the digestive tract’s movement, leading to delayed gastric emptying. This slower emptying rate means food and liquids remain in the stomach longer, increasing the volume available for potential aspiration.
Standard Fasting Guidelines
Fasting guidelines vary depending on the type of intake.
Clear Liquids
For clear liquids, such as water, clear fruit juices without pulp, black coffee or tea without milk, and electrolyte drinks, a two-hour fasting period is generally recommended. Clear liquids empty quickly from the stomach, posing a lower aspiration risk.
Milk and Formula
Breast milk typically requires four hours. Infant formula or non-human milk generally requires six hours.
Solid Foods
Solid foods, including light meals, usually require six to eight hours. Heavier or fatty meals, which take longer to digest, may necessitate eight hours or more.
These are general recommendations; always follow the specific instructions from your healthcare team, as these are tailored for individual safety.
Importance of Adhering to Instructions
Adhering to preoperative fasting instructions is important for patient safety during any procedure involving anesthesia. These guidelines minimize the risk of serious complications, particularly pulmonary aspiration. If food or liquids are consumed accidentally before the scheduled fasting period ends, immediately inform the healthcare team. Concealing this information can compromise safety and lead to unforeseen risks.
Failure to follow fasting protocols can result in surgery delay or cancellation. This precaution prevents aspiration and its severe outcomes. Proceeding with anesthesia when fasting guidelines have not been met significantly increases the risk of lung injury, prolonged hospital stays, or even mortality. Following these instructions helps ensure the procedure can proceed as planned with the highest level of safety.