Answering to the question "Why do you have to fast before surgery?"

As long as I know the minimum time needed by the patient to fast is 8 hours before the surgery (for solid food). Why?

It is because of the anesthesia. Anesthesia is given to alleviate pain during surgery so that surgery can be performed well without “torturing” the patients. There are 2 types of anesthesia that can be done. They are general anesthesia and non-generalized anesthesia.

There are several drugs needed for general anesthesia e.g midazolam (benzodiazepine group- anti anxiety and co-induction drug), fentanyl (opioid group served as pain killer and co-induction drug), propofol (induction drug-induced unconsciousness), and rocuronium bromide (muscle relaxant). Other inhalant drugs are needed to maintain the unconsciousness level.

As it is mentioned above, muscle relaxant such as roccuronium bromide is used during general anesthesia. This drug has a property to paralyze diaphragma muscle (muscle used for breathing) and Lower esophageal sphincter muscle (muscle located in the distal part of esophagus- during normal condition, it contracts to prevent regurgitation of food in the stomach to esophagus). ‘The paralyzing effect of lower esophageal sphincter muscle will lead to regurgitation of stomach content to esophagus. This content can irritate the esophagus. More than that, stomach content can be regurgitated to respiratory tract and obstruct the tract which can cause a blockade of air flow. This will result in a condition known as hypoxemia (low Oxygen content in the blood). Moreover untreated condition will lead to Acute Lung Failure and death.

Fasting for minimum 8 hours can empty the content of the stomach which is a form of anticipation from a regurgitating event of stomach content during anesthesia used in surgery.

So why some people also need to fast although they are not undergone general anesthesia. Even though they are not undergone general anesthesia there could be problem that sometimes need general anesthesia to be done on a patient that is previously having non-generalized anesthesia.