If you have ever had elective surgery, you were probably told not to eat or drink anything after midnight prior to surgery. Historically, this rule was in place to minimize and/or avoid complications from perioperative pulmonary aspiration. Stomach contents including undigested food and/or gastric acid enters the lungs, it can lead to major problems ranging from respiratory compromise, aspiration pneumonia, or even death in extreme cases. To combat these risks, the standard clinical practice was to fast/abstain from consuming liquids and solids for a specified period of time in combination with prescribing drugs to help reduce gastric volume and acidity. The new guidelines state that none of these drugs be routinely recommended.

The American Society of Anesthesiology (ASA) updated its guidelines due to new data that demonstrates advantages to drinking clear liquids until 2 hours before surgery. These guidelines apply to procedures that require regional anesthesia, general anesthesia, or procedural sedation and analgesia.

There are several benefits of drinking clear liquids up to two hours before surgery. The first and most obvious is that patients will be less thirsty (on top of being hungry) and will be more comfortable going into the operation.

Additionally, the improved hydration status will make veins more easily accessible for IV placement and potentially lead to less hemodynamic instability with the induction of anesthesia. Adequate hydration also decreases the incidence of postoperative nausea and vomiting (PONV).

A less obvious, but significant benefit is that studies actually show improved gastric emptying and a more neutral gastric pH. By diluting the acid in the stomach, there is less damage to the lungs in the event that an aspiration occurs because the degree of chemical pneumonitis is more severe with a lower, more acidic pH of gastric secretions.

Despite these advantages, these recommendations have yet to be put into practice in many facilities. Some of this may be due to a knowledge gap, but some feel that the more nuanced the instructions, the greater possibility for miscommunication or errors. Old habits die hard and some physicians may not fully appreciate the benefits shown with the new data. In reality, it is actually safer to drink clear liquids up to two hours prior to surgery since the improved gastric emptying will leave less volume in the stomach and whatever remains will actually be less acidic and thus less damaging to the lungs if aspirated!

It is essential to provide clear definitions of “clear liquids”. These include water, juices without pulp, and black coffee. Adding cream to coffee disqualifies the drink as a clear liquid and will add delays of six to eight hours although there is one study in the British Journal of Anaesthesia in 2014 that showed no difference in gastric emptying with the addition of milk to tea. Though it should be obvious, “clear liquids” do not include alcohol. Chewing gum is also prohibited since the act of chewing actually stimulates gastric acid secretion. It is also important to understand that the quantity of clear liquids consumed does not matter as long as the patient quits drinking two hours prior to their procedure.

In addition to performing a preoperative evaluation, medical professionals should inform patients of the updated fasting requirements and the reasons behind them in advance of their procedure. They should discuss that drinking clear liquids up to two hours before surgery has many proven benefits. These are the  recommendations of the ASA NPO Guidelines and we need to do a better job implementing them. The next time you read “pre-op instructions” that say not to even brush your teeth for fear of swallowing even a sip of water, think again!


“Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration: Application to Healthy Patients Undergoing Elective Procedures: An Updated Report by the American Society of Anesthesiologists Task Force on Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration*.” Anesthesiology 3 2017, Vol.126, 376-393. http://anesthesiology.pubs.asahq.org/article.aspx?articleid=2596245