What Is Preoperative Fasting?

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  • Written By: Mary McMahon
  • Edited By: Shereen Skola
  • Last Modified Date: 17 September 2019
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Preoperative fasting reduces the risk of regurgitating and inhaling the stomach contents by limiting the amount of material present in the stomach. Patients may be advised to take nothing by mouth for a set number of hours before a scheduled surgery. Precise guidelines on the topic have been a subject of debate due to changes in anesthesia technique, and a number of studies with varying results have offered unclear information for researchers. Individual patients may have particular risk factors that make them a cause for concern, requiring a case-by-case evaluation.

While patients are under anesthesia, they may be at risk of partially regurgitating and inhaling the contents of the stomach, which can be dangerous even when only a small amount of fluid is involved. Preoperative fasting can help reduce this risk. Antacid medications may also be advised, so that if some inhalation does occur, the fluid won’t be as acidic, which can limit damage to the lungs. Changes in anesthesia approaches have made this risk less likely across the board, and have reduced the need for draconian preoperative fasting guidelines.

As a general rule, people over three years old shouldn’t have solids within six hours of surgery, and should avoid clear liquids for two to four hours. In an emergency, the need to perform surgery outweighs concerns about when the patient last ate, although a nasogastric tube may be used to suction out stomach contents. For young children and infants, it may be permissible to eat closer to surgery.


Older adults, people with stomach disorders, and individuals who are overweight are at increased risk of regurgitating during surgery or in postoperative recovery. They could potentially aspirate, inhaling some of the stomach contents. The increased risk may lead a surgeon to request that the patient observe more strict preoperative fasting guidelines to ensure that the stomach is as empty as possible. This protects the patient, although it can be uncomfortable. People with concerns about their ability to adhere to recommended guidelines can talk to their surgeons to discuss their options, and should always tell their doctors if they ate inside the guideline.

Diabetic patients and other people who may have trouble with fasting may be special cases. While they still need to follow preoperative fasting requirements, they may need to prepare prior to surgery to reduce the risk of feeling unwell while fasting. For certain surgeries, like those involving the gastrointestinal tract, in addition to fasting the patient may need to follow a special diet for several days before surgery to clear the stomach and intestines.



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