China Anesthesia Week | Why are you not allowed to eat before surgery? Can you drink water?

March 27 to April 2, 2023 is the 7th China Anesthesia Week, with the theme of "Respect for Life, Doctors and Patients as Together - Tell Good Anesthesia Stories and Contribute to a Healthy China", aiming to popularize anesthesia science and promote the positive energy of the discipline.

When it comes to anesthesia, many people may have the question "Why can't you eat before surgery?"

When we or our family members are about to have surgery, we always think that we should have a good meal that is nutritious, delicious and tasty. After all, surgery will damage our vitality, and we will have to eat a light diet after surgery, so of course we have to eat better now.

But one day before the operation, the anesthesiologist will come to your bedside to shatter your "beautiful dream" and say, "What are you thinking about? You need to abstain from food and drink before the operation!"

01

Why do I need to fast before surgery?

The main purpose of fasting before surgery is to allow the patient to empty the gastric contents and prevent reflux aspiration after anesthesia.

Reflux aspiration is the process by which residual stomach contents return to the esophagus and mouth and then enter the trachea and lungs.

Once reflux aspiration occurs, it is very dangerous. In mild cases, the acid inhaled into the lungs can cause lung damage and lead to aspiration pneumonia.

In severe cases, the airway is blocked, leading to mechanical airway obstruction or even suffocation, which will endanger our lives in a short period of time.

Studies have shown that approximately two-thirds of patients who experience regurgitation aspiration during surgery eventually die or suffer irreversible lung damage[1].

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In addition, some patients undergoing gastrointestinal surgery need to fast for a longer period of time before surgery in order to clear intestinal contents and ensure intestinal cleanliness, and also need to take oral laxatives and other intestinal preparations;

This not only facilitates surgical operations, but also effectively reduces the incidence of postoperative infection.

02

Why don't you have reflux or aspiration while sleeping?

And what happens during anesthesia?

Our esophagus and airway open together at the pharynx, but there are three barriers that prevent food from passing from the stomach to the lungs:

The first barrier is a trap door at the airway opening, the epiglottis. Physiologically, when we swallow, the epiglottis closes the airway opening.

Therefore, the food and water we swallow will smoothly enter the stomach through the esophagus;

The second barrier is the lower esophageal sphincter (LES) where the esophagus and stomach join. Our stomach is like a big bag.

When food enters the stomach, the lower esophageal sphincter contracts, like tying the mouth of a bag filled with food, thus preventing the stomach contents from flowing back into the esophagus.

The third barrier is the cough reflex. When a small amount of foreign matter enters the respiratory tract and stimulates the airway mucosa, we will cough reflexively. At this time, high-pressure gas is ejected from the airway, which can expel the foreign matter in the respiratory tract and prevent more foreign matter from entering.

Sometimes when we drink water, it accidentally goes into our trachea, causing us to choke and cough violently. This is the protective reflex at work [2].

But when we are anesthetized, these three barriers will lose their function. If there is food or water left in our stomach at this time:

The lower esophageal sphincter relaxes, the mouth of the bag is opened, and food refluxes into the esophagus and mouth;

Unable to swallow, the "trap door" epiglottis cannot be closed, and food that flows into the mouth is sucked into the airway during breathing;

Without the ability to cough and high-pressure gas to clear and block foreign objects, food will continue to block the airway, causing suffocation or lung infection.

03

Do all surgeries require fasting before surgery?

Not all surgeries require fasting before surgery. Local anesthesia surgery does not affect the function of the gastrointestinal tract, so fasting before surgery is usually not necessary.

However, many situations may occur during the operation, such as drug allergy, enlarged incision, etc. In order to ensure the smooth progress of the operation and the safety of the patient's life, the doctor may change the anesthesia method at any time.

Therefore, when the doctor still tells you not to eat or drink before the anesthesia surgery, remember to follow the doctor's instructions.

If you are not sure whether you can eat or drink before the operation, you can communicate with the doctor and nurse in charge before the operation.

04

Is it true that the longer you fast, the safer it is?

Although fasting before surgery can reduce the occurrence of reflux aspiration during surgery, fasting for too long can also cause many problems:

Increased discomfort such as irritability, thirst, hunger, and fatigue increase the patient's preoperative anxiety;

It may cause hypoglycemia, insulin resistance, etc., which will have a negative impact on the body;

Insufficient effective circulating blood volume will make hypotension more likely to occur during anesthesia, and the safety of anesthesia and surgical tolerance will also be affected [3]. Therefore, the longer the preoperative fasting time, the better.

The fasting time is determined by the time it takes the stomach to empty different foods. Depending on the type of food, the longer the stomach emptying time, the longer the fasting time should be.

According to the Chinese Clinical Practice Guidelines for Enhanced Recovery After Surgery released in 2021, the preoperative fasting time is 2-4-6-8 principle [4]:

2: You can drink a small amount of transparent liquids, such as water, juice without residue, etc., more than 2 hours before anesthesia (note: alcoholic beverages are not included);

4: Babies can be fed breast milk more than 4 hours before anesthesia;

6: Easily digestible carbohydrates such as toast, steamed bread, porridge, etc. can be eaten more than 6 hours before anesthesia. Infants fed with cow's milk and formula milk also need to fast for at least 6 hours;

8: Indigestible solids, mainly meat and fried foods, require fasting for at least 8 hours.

It is important to note that this guideline is intended for healthy people who do not have comorbidities that affect gastric emptying or other medical factors that require higher fasting requirements.

If there is concurrent diabetes, pregnancy, esophageal disease, intestinal obstruction, long-term use of opioid analgesics, or obesity, an individualized fasting plan needs to be developed based on the patient's specific situation.

05

What if I take long-term oral medication?

First, not all drugs can be taken before surgery. Some drugs may increase the risk of anesthesia or surgical complications, so they need to be stopped for a period of time before surgery or replaced with other drugs.

However, some drugs may cause adverse reactions if suddenly stopped after long-term use, so they should continue to be used until before surgery.

Therefore, doctors need to have a comprehensive understanding of our drug usage records. Telling them the truth about our drug use can better protect our safety during surgery and also help them understand the specific circumstances of drug discontinuation.

If you need to take oral medications on the morning of surgery, you can take a sip of water to wash them down. This does not increase the risk of reflux aspiration.[5]

06

What should I do if I cannot fast for emergency surgery?

Emergency surgery refers to surgery that is urgent and needs to be performed in the shortest possible time, otherwise it may be life-threatening.

In this case, surgeons and anesthesiologists will weigh the risks and benefits between "reflux aspiration" and "delayed surgery" based on actual circumstances.

If the surgery is considered urgent and there is no time to wait for the fasting period, the anesthesiologist will treat the patient as a "high-risk group for reflux aspiration", develop an anesthesia plan with less risk, and take appropriate preventive measures to reduce the risk of aspiration.

References:

[1] Perlas A, Arzola C. Pulmonary Aspiration of Gastric Contents: Can We Improve Patient Outcomes? Anesthesiology. 2021 Aug 1;135(2):209-211.

[2] Lee AS, Lee JS, He Z, Ryu JH. Reflux-Aspiration in Chronic Lung Disease. Ann Am Thorac Soc. 2020 Feb;17(2):155-164.

[3] Liu Cheng, Yang Qiong, Wang Ning. Discussion on fasting and drinking before elective surgery for patients[C]//Chinese Nursing Association. Creating a patient safety culture - Proceedings of the 15th National Operating Room Nursing Academic Exchange Conference of the Chinese Nursing Association (Volume 2). 2011:3.

[4] Chinese Clinical Practice Guidelines for Enhanced Recovery After Surgery (2021) (I)[J]. Journal of Peking Union Medical College, 2021, 12(05): 624-631.

[5] Joshi GP, Abdelmalak BB, Weigel WA, Harbell MW, Kuo CI, Soriano SG, Stricker PA, Tipton T, Grant MD, Marbella AM, Agarkar M, Blanck JF, Domino KB. 2023 American Society of Anesthesiologists Practice Guidelines for Preoperative Fasting: Carbohydrate-containing Clear Liquids with or without Protein, Chewing Gum, and Pediatric Fasting Duration-A Modular Update of the 2017 American Society of Anesthesiologists Practice Guidelines for Preoperative Fasting. Anesthesiology. 2023 Feb 1;138(2):132-151.

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