Preoperative Fasting | All You Need to Know

During the 8 to 12 hours before surgery, you may have been instructed not to eat or drink anything. Unless you have been told it is okay to take your medications with a few sips of water the morning of surgery, no food or drink simply means no food or drink!

A beautiful young woman in a white dress with a watch in her hand, eating a hamburger in front of a large number of fruits

Fasting Before Surgery: Reasons, Complications, and Instructions

Patients are asked not to eat prior to their procedure for a number of reasons, including potential complications that could arise if food is inside the stomach during the administration of anesthesia.
Any patient undergoing surgery or procedure that requires anesthesia, should have an empty stomach beforehand in order to prevent nausea and prevent any food or liquid from entering the lungs. Indeed, patients’ safety is the main purpose of creating rules about preoperative fasting.

Why should I fast before the surgery?

There are many different types of surgeries; Some are done under local anesthesia, others require regional or general anesthesia.
Normally, a patient is not allowed to eat or drink before the operation that is performed under general anesthesia.

Under general anesthesia, the normal throat reflexes and the gastrointestinal tract movements are temporarily stopped.
If the patient’s stomach is full in this condition, there is a risk of vomiting or bringing food into the throat.
Consequently, food particles may easily make their way into the lungs or airways and cause suffocation or damage the respiratory system.

Even in local anesthesia, due to the possibility of intraoperative problems such as the patient waking up during the operation or not cooperating with the medical team, the patient might be placed under general anesthesia.
Therefore, all patients are normally asked to fast before the operation, regardless of what type of anesthesia is planned for them.

an infographic image showing the reasons of fasting before a surgery and not eating and drinking before anesthesia

Reasons of fasting before surgery

How long do I have to fast before surgery?

The amount of time a patient is not allowed to eat before surgery varies according to age, individual condition, type of surgery, and type of food consumed at least a day prior to operation.
For instance, infants can be breastfed up to 4 hours before surgery, or if the patient has eaten high-protein and fatty foods as his/her last meal, the fasting period should be longer because these foods take longer to digest.

Normally, one should not eat for 8 to 12 hours and not drink for at least 2 hours before the operation.
Unless the patients have to take medication and the doctor permits them to consume a small amount of water. Even chewing gum is not allowed during the fasting period.

Of course, there are always exceptions. For example, patients with diabetes need to eat regularly to prevent hypoglycemia.
In these cases, you must inform your doctor about your condition so that he or she can tell you the necessary instructions to handle low blood sugar during the fasting period.
You should also tell your healthcare provider if you are taking certain medications.

A female patient in a hospital blue dress, eating some fruits 8 hours before her surgery

You should not eat for 8 to 12 hours and not drink for at least 2 hours before the surgery.

How does prolonged fasting affect surgery?

Not eating or drinking excessively may cause other problems. If the fasting state is prolonged, in addition to mental problems and increased stress, there will be a risk of dehydration, which makes the operation more dangerous, especially for children.
Prolonged fasting in women may increase the risk of hypoglycemia.
In general, long-term fasting causes abnormalities in the body’s metabolism, so fasting longer than the prescribed time is not allowed.

An anesthesiologist is the best person to determine the exact duration of fasting in order to ensure that the patient’s health is not compromised.

What am I allowed to consume before surgery?

Try to eat healthy, high-fiber foods like fruit and vegetables several days or weeks before surgery.
In addition, foods rich in vitamins, minerals, and protein are essential for your body to go through the postoperative healing process as well as possible.
Moreover, having a low-fat diet minimizes the possibility of postoperative side effects.

Avoid processed foods, red meats, alcohol, and cigarettes at least 48 hours prior to your surgery.
It is necessary to avoid overeating or eating slow-digesting foods, such as legumes and vegetables, before your 8-to-12-hour fast; otherwise, fasting will not be useful. Alternatively, have a light meal like soup.

some fruits such as tomatoes, avocados, apples, bananas and etc. that you are allowed to eat before a surgery

Try to eat healthy, high-fiber foods like fruit and vegetables, in addition to foods which are rich in vitamins, minerals, and protein several days or weeks before surgery.

You can also drink clear fluids (water, weak black tea, or black coffee NOT milk or dairy products) up to 2 hours before surgery.
Hydrating the body, preferably with water, will help you tolerate the operation significantly better. This is especially important in hot weather.

Stop Solid Foods Drink Clear Liquids Until Arrival Time
10 p.m. 4 a.m. 6 a.m.
Midnight 6 a.m. 8 a.m.
2 a.m. 8 a.m. 10 a.m.
4 a.m. 10 a.m. 12 p.m.
6 a.m. 12 p.m. 2 p.m.

What happens if I don’t fast before surgery?

A significant factor that worries anesthetists is not fasting before surgery.

The following risks may occur if you eat or drink before general anesthesia:

  • Nausea and vomiting
  • Aspiration (inhaling vomit)
  • Pulmonary complications (infection, pneumonia)
  • Asphyxiating or choking to death

What if I had an emergency operation?

In case of an emergency operation, bowel preparation (bowel prep) is done, which is a process that drains the digestive tract of food and stool. It is also a way to make sure the bowels are completely empty in order to prepare the patient for surgery.

If you are having surgery in Iran, an anesthesiologist will inform you about the necessary instructions, such as the duration of the fasting period and what foods or liquids you can have as your last meal before surgery, to avoid possible complications.

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