Preoperative

fasting Fasting is the abstention from eating and sometimes drinking. From a purely physiological context, "fasting" may refer to the metabolic status of a person who has not eaten overnight (see " Breakfast"), or to the metabolic state achieved after ...

is the practice of a

surgical Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...

patient abstaining from eating or drinking ("

nothing by mouth Nothing by mouth is a medical instruction meaning to withhold food and fluids. It is also known as nil per os (npo or NPO), a Latin phrase that translates to English as "nothing through the mouth". Variants include nil by mouth (NBM), nihil/non/nu ...

") for some time before having an

operation Operation or Operations may refer to: Arts, entertainment and media * ''Operation'' (game), a battery-operated board game that challenges dexterity * Operation (music), a term used in musical set theory * ''Operations'' (magazine), Multi-Ma ...

. This is intended to prevent

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

contents from getting into the

windpipe The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends from the la ...

and

lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...

(known as a

pulmonary aspiration Pulmonary aspiration is the entry of material such as pharyngeal secretions, food or drink, or stomach contents from the oropharynx or gastrointestinal tract, into the larynx (voice box) and lower respiratory tract, the portions of the respira ...

) while the patient is under

general anesthesia General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...

. The latest guidelines do not support preoperative fasting, as there is no difference in residual gastric fluid volume, pH or gastric emptying rate following semi-solid meals or drinks, whether in obese or lean individuals.

Pulmonary aspiration

The main hypothesized benefit of preoperative fasting is to prevent

of stomach contents while under the effects of general anesthesia. Aspiration of as little as 30–40 mL can be a significant cause of suffering and death during an operation and therefore fasting is performed to reduce the volume of stomach contents as much as possible. Several factors can predispose to aspiration of stomach contents including inadequate anesthesia,

pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ca ...

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...

, difficult airways, emergency surgery (since fasting time is reduced), full stomach and altered

gastrointestinal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

mobility. Increased fasting times leads to decreased injury if aspiration occurs. The latest guidelines do not support preoperative fasting, as there is no difference in residual gastric fluid volume, pH or gastric emptying rate following semi-solid meals or drinks, whether in obese or lean individuals.

Gastric conditions

In addition to fasting,

antacid An antacid is a substance which neutralizes stomach acidity and is used to relieve heartburn, indigestion or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhea. Marketed antacids contain salts of alumi ...

s are administered the night before (or in the morning of an afternoon operation) and then once again two hours prior to surgery. This is to increase the pH (make more neutral) of the

acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

present in the stomach, helping to reduce the damage caused by pulmonary aspiration, should it occur. H2 receptor blockers should be used in high-risk situations and should be administered in the same timing intervals as antacids.

Gastroparesis Gastroparesis (gastro- from Ancient Greek γαστήρ – gaster, "stomach"; and -paresis, πάρεσις – "partial paralysis"), also called delayed gastric emptying, is a medical disorder consisting of weak muscular contractions (peristalsis) ...

(delayed gastric emptying) may occur and is due to

metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

causes (e.g. poorly controlled

diabetes mellitus Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

), decreased gastric motility (e.g. due to head injury) or pyloric obstruction (e.g.

pyloric stenosis Pyloric stenosis is a narrowing of the opening from the stomach to the first part of the small intestine (the pylorus). Symptoms include projectile vomiting without the presence of bile. This most often occurs after the baby is fed. The typical a ...

). Delayed gastric emptying usually only affects the emptying of the stomach of high-

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

foods such as vegetables. Gastric emptying of clear fluids such as water or black

coffee Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulant, stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world. S ...

is only affected in highly progressed delayed gastric emptying. Usually,

gastroesophageal reflux Gastroesophageal reflux disease (GERD) or gastro-oesophageal reflux disease (GORD) is one of the upper gastrointestinal chronic diseases where stomach content persistently and regularly flows up into the esophagus, resulting in symptoms and/ ...

(GERD) may be associated with delayed gastric emptying of solids, but clear liquids are not affected. Raised intra-abdominal pressure (e.g. in pregnancy or obesity) predisposes to regurgitation. Certain drugs such as

opiates An opiate, in classical pharmacology, is a substance derived from opium. In more modern usage, the term ''opioid'' is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain (including antagonist ...

can cause marked delays in gastric emptying, as can

trauma Trauma most often refers to: * Major trauma, in physical medicine, severe physical injury caused by an external source * Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic i ...

, which can be determined by certain indicators such as normal bowel sounds and patient hunger.

Minimum fasting times

The minimum fasting times prior to surgery have long been debated. The first proposition came from British anesthetists stating that patients should have

from midnight. However, since then, the

American Society of Anesthesiologists The American Society of Anesthesiologists (ASA) is an educational, research and scientific association of physicians organized to raise the standards of the medical practice of anesthesiology and to improve patient care. As of 2021, the organizat ...

(ASA), followed by the Association of Anaesthestists of Great Britain and Ireland (AAGBI), recommended new fasting guidelines for the minimum fast prior to surgery. This was based upon evidence by Canadian anesthesiologists who found that drinking clear fluids two hours prior to surgery decreased pulmonary aspiration compared to those nil by mouth since midnight. The following are the recommended guidelines for nil by mouth prior to surgery in healthy patients: When anaesthesia is required in an emergency,

nasogastric aspiration Nasogastric intubation is a medical process involving the insertion of a plastic tube (nasogastric tube or NG tube) through the human nose, nose, down the oesophagus, and down into the stomach. Orogastric intubation is a similar process involving ...

is usually performed to reduce gastric contents and the risk of its pulmonary aspiration.

Unrestricted clear fluids

Fasting guidelines often restrict the intake of any oral fluid after two to six hours preoperatively. However, it has been demonstrated in a large retrospective analysis in

Torbay Hospital Torbay Hospital is the main hospital of South Devon, England. It is managed by the Torbay and South Devon NHS Foundation Trust. History The hospital was founded as the Torbay Hospital, Provident Dispensary and Eye Infirmary in 1844. Constructi ...

that unrestricted clear oral fluids right up until transfer to theatre could significantly reduce the incidence of postoperative nausea and vomiting without an increased risk in the adverse outcomes for which such conservative guidance exists.

Public information

A 2016 systematic review found that the information on the internet often provided inaccurate and out-of-date recommendations on preoperative fasting.

References

{{reflist Surgery Fasting Diets