Preoperative fasting in adults

INTRODUCTION — Patients are routinely asked to fast before anesthesia to minimize the risk of aspiration of stomach contents and to reduce the severity of pulmonary effects should aspiration occur. This topic will discuss the rationale for preoperative fasting, physiology of stomach emptying, and preoperative fasting guidelines for adults. Preoperative fasting in children is discussed separately. (See "Preoperative fasting in children and infants".)

Other practices that may reduce the incidence of aspiration during and after anesthesia are discussed separately. (See "Rapid sequence induction and intubation (RSII) for anesthesia" and "Rapid sequence induction and intubation (RSII) for anesthesia", section on 'Preoperative antacids'.)

RATIONALE FOR PREOPERATIVE FASTING — The goal for preoperative fasting is to reduce the risk of aspiration of gastric contents. Aspiration of gastric contents is associated with increased perioperative morbidity and mortality [1-3], with highest risk associated with high volume, acidic, or particulate aspiration. Aspiration can occur during any type of anesthesia, as a result of eliminated or attenuated respiratory reflexes due to sedating medications.

●Gastric volume – Historically, a gastric volume greater than 2.5 mL/kg has been the marker of an “at risk” stomach volume, but other limits have also been used (eg, 25 or 40 mL) [4,5]. Several studies using gastric ultrasound have found a gastric fluid volume of approximately 1.5 mL/kg in healthy fasting patients; as such, some authors use a volume ≤1.5 mL/kg to define an empty stomach [6-8]. Conventional wisdom holds that restricting oral intakes decreases gastric volume and therefore aspiration risk; however, there is not a known gastric volume that either eliminates risk or places a patient at particularly undue risk.

●Acid aspiration – Based on animal studies, aspiration of highly acidic fluid as is typically found in the stomach is more injurious than aspiration of pH neutral fluids [5,9]. A pH of 2.5 is used in many studies as another surrogate endpoint that is associated with increased risk of pulmonary injury if aspiration occurs. (See "Aspiration pneumonia in adults", section on 'Fluids'.)

●Particulate aspiration – Particle aspiration may cause injury by two mechanisms; large particle aspiration can cause airway obstruction, and particles can also cause inflammatory damage [10]. Although particulate aspiration has conventionally been associated with increased risk of pulmonary damage, there are limited data on the pulmonary effects of particulate matter, separate from the sequalae of acidic contents.

Incidence and outcome of aspiration during anesthesia — Large retrospective reviews suggest that aspiration occurs in between 1 in 3000 to 7100 anesthetics, with significant morbidity in 1 in 7200 to 16,500, and mortality related to aspiration in 1 in 72,000 to 100,000 anesthetics [1,11]. Aspiration occurs most commonly during induction of general anesthesia, but can also happen during maintenance and extubation [12,13].

The aspiration of gastric contents, albeit rare, can cause significant morbidity and mortality [1-3,11].

●In reports submitted to the Fourth National Audit Project (NAP 4), a prospective registry that collected and reported major airway complications in all National Health Service Hospitals in the UK, aspiration was responsible for 50 percent of deaths and was the most common cause of mortality related to airway complications [3].

●In a review of 133 cases of aspiration reported to the Australian Anaesthetic Incident Monitoring Study, 30 percent of aspiration events required admission to the intensive care unit (ICU) or high dependency unit, and five patients (4 percent) who aspirated died [13].

●In a review of 115 aspiration events in the Anesthesia Closed-Claims Project database from 2000 to 2013, 57 percent of aspirations resulted in death, and another 14 percent resulted in permanent severe injury [12]. Aspiration accounted for 5 percent of all anesthesia-related claims during that time period.

IMPLICATIONS OF EXCESSIVE FASTING — Prolonged and unnecessary fasting should be avoided. Excessive fasting may lead to patient discomfort (ie, thirst and hunger), and may also result in postoperative insulin resistance, exaggerated inflammatory markers, and increased catabolism [14], though the evidence for these effects is limited. (See "Enhanced recovery after colorectal surgery", section on 'Fasting guidelines'.)

Despite current recommendations for fasting, patients often fast much longer than guidelines suggest or allow [15-17]. As an example, in a single-center prospective observational study of over 750 adult and pediatric surgical patients, median fasting time for solids was 14.1 hours (95% CI 12-16 hours) and for liquids was 9.8 hours (95% CI 3.8-13.2 hours) [15]. No clinical outcomes were reported.

PHYSIOLOGY OF STOMACH EMPTYING — Several methods have been used to determine gastric emptying times for various substances. Regardless of the method used, gastric emptying time and the stomach volume in appropriately fasted patients varies significantly [6,7].

Methods used to measure stomach emptying or volume — Several methods have been used to assess stomach volume and emptying in perioperative studies. Here we describe several of the most common methods.

●Gastric aspiration – Gastric aspiration is commonly used to measure stomach volume during anesthesia, as it is simple and requires no imaging or special equipment. Gastric aspiration can be performed blindly using an oral or nasal gastric tube, or it can be visualized using a gastroscope. In a small study that compared blind versus visualized gastric aspiration in patients undergoing general anesthesia, blind aspiration significantly underestimated true gastric volume [18].

●Radiologic studies – Scintigraphy is considered the gold standard for evaluating quantitative gastric emptying. Scintigraphy can be performed by having the patient ingest radionuclide tracers, followed by imaging with radiographs or fluoroscopy [19], or by having the patient ingest gadolinium, followed by magnetic resonance imaging (MRI) [20], to assess gastric volume and emptying.

●Paracetamol absorption – Paracetamol absorption is an indirect measurement of stomach emptying. Paracetamol is poorly absorbed in the stomach but rapidly absorbed in the small intestine [21]. Thus, blood levels of paracetamol reflect the rate of gastric emptying. The patient ingests a standardized dose of paracetamol, and blood levels are measured over time. Paracetamol absorption correlates well with gastric emptying of liquids as assessed by scintigraphy [22].

●Gastric ultrasound – Gastric ultrasound has been employed as a noninvasive way to assess the volume and character of gastric contents before anesthesia. Although not commonly employed as part of routine preoperative assessment, gastric ultrasound may be useful when fasting history is unknown or in question, or for patients with risk factors for delayed gastric emptying. The results can be used to reassure clinicians that the volume of stomach contents is felt to be sufficiently low to minimize aspiration risk or, conversely, to support a decision to delay elective surgery in a patient with increased volume or visualized solid matter. However, to date, there are no guidelines for the clinical use of gastric ultrasound, and results have not been correlated with the risk of aspiration.

Gastric ultrasound is discussed in detail separately. (See "Overview of perioperative uses of ultrasound", section on 'Gastric ultrasound'.)

Clear liquids — Clear liquids include water, juices without pulp, coffee or tea without milk or cream, and carbohydrate drinks.

Clear liquids and gastric secretions move rapidly out of the stomach. The 50 percent emptying time of water is approximately 12 minutes [23]. Compared with water, glucose-containing clear fluids move more slowly during the first 60 minutes, but gastric transit is consistently complete after 90 minutes [24]. Patients who have fasted overnight have gastric volumes similar to those who drink clear liquids, water, clear juices, coffee, tea, or carbohydrate drinks up to two hours before surgery [25-31].

Contemporary fasting guidelines allow ad-lib access to clear liquids up to two hours prior to surgery for adults, and even later for children. (See 'Fasting guidelines' below and "Preoperative fasting in children and infants", section on 'Fasting guidelines at the author's institution'.)

Multiple randomized trials have found that patients who drink clear liquids two to four hours prior to surgery experience less hunger and thirst than those who fast for more than four hours [32-35]. Some studies have found that patients who ingest carbohydrate-rich clear liquids up until two hours prior to induction of anesthesia have less thirst, hunger, and anxiety compared with those who drank water or fasted [36,37].

Other liquids — Non-clear liquids include milk products, formula, and other liquids with suspended particles. For preoperative fasting, non-clear liquids are considered distinct from clear liquids. In particular, milk is treated more like a solid because it can curdle into particles in the stomach. Gastric emptying of nonhuman milk has been thought to be similar to emptying of solid food, as milk contains varying amounts of protein and fat, both of which increase gastric emptying time [38,39]. However, in a study that used gastric ultrasound to assess stomach emptying in healthy volunteers, emptying of nonhuman milk was similar to emptying of a similar volume of orange juice if both were adjusted to the same caloric content [40].

There are no studies evaluating the speed with which plant-based milk products (eg, oat, nut, coconut) are emptied. Thus, all forms of nonhuman milk are treated similarly for the purpose of preoperative fasting guidelines.

Whether a small amount of milk added to coffee or tea affects gastric emptying or increases the risk or potential consequences of aspiration is controversial. Coffee or tea with milk has traditionally been considered a non-clear liquid for the purpose of fasting guidelines, and patients who added milk to coffee or tea within six hours of surgery have had surgery delayed. However, the need for increased fasting after drinking a small amount of milk has been questioned.

●In a randomized trial that used gastric ultrasound and paracetamol absorption to assess gastric emptying, gastric emptying was similar in patients who drank 250 mL of tea with 50 mL of milk, versus 300 mL of tea without milk [41]. For both groups, mean stomach volume returned to baseline within 90 minutes.

●In another randomized trial, 50 nonlaboring pregnant patients were assessed with gastric ultrasound for two hours after drinking 250 mL of water versus 250 mL of tea with milk [42]. Mean gastric volume returned to baseline by 90 minutes in both groups.

Contemporary fasting guidelines allow non-clear liquids up to six hours prior to surgery for adults. Guidelines for formula and breast milk for children are discussed separately. (See 'Fasting guidelines' below and "Preoperative fasting in children and infants", section on 'Fasting guidelines at the author's institution'.)

Solid foods — Solid food empties from the stomach more slowly than liquids, and variably depending on nutritional composition. Patient comorbidities and medications also affect the speed of gastric emptying. Normal gastric emptying begins roughly one hour after ingestion and continues linearly, with one half of the solid food passing into the duodenum in approximately two hours [43]. In one study, the median time for the disappearance of solid particles was 210 minutes after a light breakfast of toast, coffee without milk, and pulp-free juice [43]. Gastric emptying is slowed by increased food weight, higher caloric density, and higher fat content, as well as in women and older patients [44-49]. As an example, in one study, increasing meal size from 300 to 1700 grams increased the half-emptying time from 77 to 277 minutes [44].

Contemporary fasting guidelines allow “light” (non-fatty) solid food up to six hours prior to surgery, and meat or fatty foods up to eight hours prior to surgery. (See 'Fasting guidelines' below.)

Chewing gum — Chewing gum increases saliva production and stimulates gastric secretions. However, the effect of chewing gum on gastric volume and acidity is probably inconsequential. In a 2015 meta-analysis of four randomized trials including 287 surgical patients, chewing gum resulted in a statistically significant but likely clinically irrelevant increase in gastric volume (mean difference 0.21 mL/kg, 95% CI 0.02-0.39) [50]. Stomach pH was similar in patients who chewed gum and those who did not. In a subsequent prospective observational volunteer study, gastric volume measured with gastric ultrasound was similar before and after chewing gum for one hour [51].

Chewing gum that is swallowed is considered a solid, and is treated as such for the purpose of fasting guidelines. (See 'Our approach' below.)

Alcohol — Although most types of alcohol are clear, alcohol is not considered a clear liquid for most institutional fasting guidelines, including the guidelines at the authors’ institution. This is because ingestion of alcohol often delays gastric emptying and decreases small intestine motility [52].

FASTING GUIDELINES — Pre-anesthesia fasting guidelines apply to all adult patients having an elective surgery or procedure. They are intended for any procedure performed under monitored anesthesia care, regional anesthesia, neuraxial anesthesia, or general anesthesia. In general, generic fasting guidelines apply to patients without coexisting conditions or diseases that can affect gastric emptying or the risk of aspiration (eg, laboring pregnant patients, patents with diabetes or gastroesophageal reflux disease [GERD]). For such patients, conventional fasting intervals may require modification.

Our approach — Fasting guidelines are usually created on an institutional basis, and often represent multidisciplinary consensus among surgery, anesthesia, endoscopy, radiology, and nursing services. Our institutional guidelines for adults are as follows:

●Fatty food or meat – We suggest fasting for eight hours.

●Light meal – We suggest fasting for six hours.

●Nonhuman milk and other non-clear liquids – We suggest fasting for six hours.

●Clear liquids – We suggest fasting for two hours.

●Chewing gum – We inform patients to stop chewing gum two hours prior to sedation or anesthesia. However, we do not delay anesthesia for patients who chew gum beyond that time, unless the gum is swallowed.

●Medications – Patients should routinely take medications on the day of surgery with water or a clear liquid, ideally more than two hours prior to the scheduled procedure. For medications that must be taken within two hours of surgery (eg, forgotten doses, medications that must be administered on a strict schedule, or medications used as part of anesthesia), intravenous preparations are preferred. Oral medications within two hours of surgery should be taken with a sip of water.

For patients who must take medications with a thickened liquid and who need oral medications within six hours of surgery, options include taking the medication with gelatin or clear jelly.

●Others – We consider bowel preparation solutions to be clear liquids. We typically consider nonclear oral contrast to be a non-clear liquid, though some radiologists require the last dose ingested within four hours of the procedure. In that case, the anesthesiologist will have to decide whether to perform rapid sequence induction and intubation for general anesthesia.

Anesthesia society guidelines — Preprocedural fasting guidelines have been developed by various anesthesia societies and other organizations around the world [53-60]. The fasting guidelines are primarily based on expert opinion and the physiology of gastric emptying, without evidence that following recommendations improves clinical outcomes.

All society guidelines allow clear liquids until two hours prior to anesthesia and restrict solid food within six hours [53-60]. Further details appear in a table (table 1).

Patient instructions — Instructions given to patients should reflect the needs of the patient population and the institutional tolerance for cancellation or delay. In some cases, instructions given to patients may be more restrictive than the criteria that will be used to decide whether to proceed with surgery. As an example, patients whose surgical time may be moved earlier than planned may be instructed to stop eating and drinking earlier than required by the scheduled surgical time.

Patients who have not followed the recommended fasting guidelines may have elective procedures delayed or rescheduled. The decision to proceed or delay a scheduled elective case should be made by the anesthesiologist after considering the implications of delaying or rescheduling a procedure, the amount, type of ingestion, and the individual risk factors for delayed gastric emptying and aspiration.

SPECIAL PATIENT POPULATIONS

Patients with gastroesophageal reflux disease — Patients with gastroesophageal reflux disease (GERD) may be at increased risk of aspiration, due to decreased lower and upper esophageal sphincter tone and impaired airway reflexes during anesthesia [12,61]. At the authors' institution, we base preoperative fasting recommendations on patient symptoms. Patients with symptomatic reflux are asked to fast for eight hours from solid food, and the standard two hours for clear liquids. It is reasonable to administer a gastrointestinal stimulant (eg, metoclopramide) and pharmacologic gastric acid suppression in these patients [54].

Optimal fasting guidelines in patients with GERD are unclear, and data are limited. Guidelines from the American Society of Anesthesiologists make no recommendation for fasting in these patients, and the guidelines from the European Society of Anaesthesiology and Intensive Care recommend using standard fasting guidelines, citing lack of definitive evidence to recommend otherwise.

Patients with obesity — Standard preoperative fasting guidelines should be followed for patients with obesity. In many studies, gastric emptying of both liquids and solids is not delayed, and in some cases, they are more rapid than normal-weight patients [62-66]. (See "Anesthesia for the patient with obesity", section on 'Aspiration prophylaxis'.)

Patients who have had bariatric surgery — Patients who have had bariatric surgery may require longer preoperative fasting times. Optimal timing of preoperative fasting for these patients has not been established, as effects of bariatric surgery on gastroesophageal reflux and stomach emptying varies, both with respect to the type of procedure and the patient response. We base the preoperative fasting intervals on the patient's symptoms and ask patients with symptoms of gastroesophageal reflux (similar to patients with GERD) to fast for eight hours for solid food. It is reasonable to administer a gastrointestinal stimulant (eg, metoclopramide) for symptomatic patients.

Patients who have had bariatric surgery may be at increased risk for aspiration due to changes in gastric or esophageal anatomy or physiology (eg, esophagitis, new or worse gastroesophageal reflux, or esophageal dilatation). (See "Bariatric operations: Late complications with subacute presentations".)

Gastroesophageal reflux may improve in patients who undergo bariatric procedures because of weight loss. However, de novo GERD may occur, particularly after sleeve gastrectomy, which is the most commonly performed weight loss surgery in the United States. (See "Bariatric operations: Late complications with subacute presentations", section on 'Acid reflux or Barrett esophagus'.)

Consistent with increased risk, a position statement from the International Society for the Perioperative Care of Patients with Obesity recommended rapid sequence induction and intubation for patients who have had bariatric surgery, and considering prophylaxis with H2 blockers and/or proton pump inhibitors for anesthesia [67]. The statement makes no recommendation for preoperative fasting.

Pregnant patients — Standard fasting guidelines should be followed for preoperative pregnant patients who are not in labor. Gastric emptying is normal in both obese and nonobese nonlaboring parturients [68-71]. In a study that used gastric ultrasound to evaluate stomach emptying in 40 full-term pregnant patients who ingested 400 mL of a clear carbohydrate drink, median stomach volume returned to pre-drink baseline by 120 minutes [72].

Gastric emptying in laboring patients is delayed, and is discussed separately. (See "Airway management for the pregnant patient", section on 'Fasting and aspiration prophylaxis'.)

Patients with diabetes — Patients with diabetic gastroparesis may benefit from a longer duration of fasting on a case-by-case basis. The incidence of gastroparesis in patients with diabetes is unknown, but estimates put it between 30 and 60 percent of diabetics [73,74]. Thus, we assess patients for symptoms of autonomic dysfunction or gastroparesis, and ask symptomatic patients to fast for eight hours from solid food before anesthesia. (See "Diabetic autonomic neuropathy of the gastrointestinal tract", section on 'Epidemiology'.)

Small studies have suggested that gastric emptying of solid food may be significantly delayed in patients with diabetic gastroparesis [75], whereas emptying of liquids may be similar to patients without diabetes [76]. Moreover, there is a poor correlation between gastric emptying of solids and liquids in these patients. In one study, indigestible solid markers were retained in the stomach six hours after a carbohydrate meal in one-half of the diabetics, although they had passed in all nondiabetics [75]. A follow-up study comparing gastric emptying of diabetics with known autonomic dysfunction against nondiabetic controls utilizing dual radionuclide scintigraphy demonstrated that the gastric emptying of liquids was preserved in the diabetic group compared to the control group [76]. Emptying of solids was still delayed but was normalized with the utilization of a pharmacologic agent.

The pathogenesis and management of diabetic gastroparesis are discussed in detail separately. (See "Diabetic autonomic neuropathy of the gastrointestinal tract", section on 'Gastroparesis'.)

Patients taking GLP-1 agonists — Delayed gastric emptying is a potential side effect of glucagon-like peptide 1 (GLP-1) receptor agonists (eg, semaglutide, liraglutide) which are used to treat diabetes and are increasingly used for weight loss. Patients who take these medications may have residual gastric contents despite preoperative fasting [77,78] and may be at increased risk of aspiration during induction of anesthesia. Nausea, vomiting, and abdominal distention are associated with increased gastric residual volumes in patients who take GLP-1 receptor agonists [78].

Optimal fasting times for patients taking GLP-1 receptor agonists have not been established [79,80], and practice varies. At the authors’ institution, we follow the 2023 consensus statement from the American Society of Anesthesiologists (ASA) [79]. The ASA suggests following standard fasting guidelines, due to lack of evidence supporting a different approach. The ASA also suggests holding the GLP-1 receptor agonist prior to anesthesia.

●For patients who have held the medication and do not have gastrointestinal (GI) symptoms, we proceed as if they had fasted appropriately.

●For patients who have not held the drug or who have symptoms of increased gastric residual volume, we discuss the risks and benefits of proceeding with the procedure. If we do proceed, we treat the patient as having a full stomach and perform rapid sequence induction and intubation as appropriate. (See "Rapid sequence induction and intubation (RSII) for anesthesia".)

●We often use gastric ultrasound to assess gastric volume in patients who have not held the drug or who have GI symptoms.

Patients receiving enteral tube feeds — Enteral feeding formulas typically contain carbohydrates, protein, and fat, so we consider tube feedings to be a fatty meal [81]. For patients receiving enteral tube feeds, the decision to stop tube feeds represents a balance between the need for nutritional support and avoiding aspiration.

●Patients with a gastric feeding tube

•Patients who are not intubated or who have an uncuffed tracheostomy tube – For these patients, we suggest stopping gastric tube feeds eight hours prior to sedation or anesthesia.

•Patients with a cuffed tracheostomy tube or endotracheal tube – It is unclear whether these patients require a period of fasting prior to nonabdominal surgery. Prolonged fasting may increase the existing catabolic rate in critically ill patients. However, this concern must be weighed against the risk of aspiration or microaspiration around a cuffed tube. Aspiration around the tube cuff is more common when the patient is placed in the supine position, as may be required for surgery [82,83]. (See "Risk factors and prevention of hospital-acquired and ventilator-associated pneumonia in adults", section on 'Patient positioning'.)

Therefore, a multidisciplinary discussion between the surgeon, anesthesiologist, and primary care team should determine the optimal time for stopping enteral feeds, taking into account the patient’s nutritional status, the type of surgery, and overall risk of aspiration on a case-by-case basis. Patients receiving tube feeds should be transported and positioned for surgery in a head-up position, if possible.

●Patients with a postpyloric feeding tube – Postpyloric feeding tubes are placed primarily for patients at high risk for aspiration, though the reduction in the incidence of pneumonia is small (see "Nutrition support in intubated critically ill adult patients: Enteral nutrition", section on 'Post-pyloric'). At our institution, once the position of the feeding tube is confirmed to be post-pyloric by radiograph, we generally continue feeding up until the patient is called for the procedure.

●Patients undergoing abdominal surgery – For these patients we stop tube feeds eight hours prior to surgery.

FASTING IN ENHANCED RECOVERY AFTER SURGERY PROTOCOLS — Major surgery is a form of stress that typically results in insulin resistance [84], which can cause hyperglycemia and associated postoperative complications. Enhanced recovery after surgery (ERAS) protocols that have been developed for various surgical procedures aim to reduce surgical stress and insulin resistance. They typically minimize the perioperative fasting period and suggest preoperative oral hydration up until two hours prior to surgery, and many ERAS protocols include as much as 500 mL of clear liquid or oral carbohydrate drink two to three hours prior to surgery. (See "Anesthetic management for enhanced recovery after major noncardiac surgery (ERAS)", section on 'Preanesthesia consultation'.)

Some studies have found that administration of a preoperative carbohydrate drink or a preoperative glucose infusion reduced the degree of insulin resistance (and resultant hyperglycemia) that typically occurs after major surgery [85-87]; improved other outcomes (eg, preserved muscle mass and earlier return of bowel function after colorectal surgery); and were associated with small reductions in hospital length of stay [88].

However, the benefits of preoperative carbohydrate administration in isolation, separate from other components of ERAS protocols, have not been confirmed. In a 2017 network meta-analysis of 43 randomized and quasi-randomized trials including over 3000 patients who underwent elective surgery and who drank the study solution within four hours of surgery, ingestion of carbohydrate solution, a placebo solution, or water resulted in a less than half a day reduction in length of hospital stay compared with fasting [89]. Postoperative complication rates, insulin resistance, and time to first bowel movement were similar among groups.

Although not well-studied, the incidence of aspiration in patients who receive oral hydration in an ERAS protocol appears to be low. There are no studies of ERAS protocols with aspiration as a primary outcome. Some studies have reported no known or suspected cases of aspiration in patients who are part of an ERAS protocol [37,85,88,90].

The available literature suggests that consumption of carbohydrate drinks as part of ERAS does not affect gastric residual volume or stomach pH [36,91-93]. As an example, in one study of 250 patients who were randomly assigned to drink 400 mL of a carbohydrate drink or a placebo drink, or to fast, before elective abdominal surgery, mean gastric residual volume and stomach pH after induction of anesthesia were similar among the groups [36]. Similarly, in a randomized trial including 64 patients who had elective benign gynecologic surgery, gastric volume assessed by ultrasound was similar in patients who fasted from midnight and those who ingested carbohydrate drinks until two hours prior to surgery [94].

SOCIETY GUIDELINES LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Preoperative fasting".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)

●Basics topics (see "Patient education: Fasting before surgery (The Basics)" and "Patient education: Anesthesia (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Rationale for preoperative fasting – Patients are asked to fast before anesthesia to reduce the risk of aspiration and the severity of pulmonary injury in the event of aspiration. Pulmonary aspiration is a rare event but carries significant morbidity and mortality. (See 'Rationale for preoperative fasting' above.)

●Physiology of stomach emptying

•Clear liquids usually empty from the stomach within 90 minutes. (See 'Clear liquids' above.)

•Gastric emptying of milk is similar to clear liquids of similar calorie content. However, for preoperative fasting, milk is treated similarly to solid food since milk curdles in the stomach. Whether a small amount of milk added to coffee or tea delays gastric emptying or increases the risk or consequence of aspiration is uncertain. (See 'Other liquids' above.)

•Gastric emptying of solid food varies widely depending on patient factors and the volume and nutrient content of the food. Gastric emptying is slowed by increased food weight, higher caloric density, and higher fat content. (See 'Solid foods' above.)

●Fasting guidelines – For most patients who undergo elective surgery with general anesthesia, regional anesthesia, or monitored anesthesia care, we use the following preoperative fasting guidelines. The following recommendations are mainly based on consensus opinion and known gastric physiology instead of high-quality studies showing a clinical benefit. Patients with risk factors for delayed gastric emptying or increased risk of aspiration may require longer fasting intervals. (See 'Our approach' above.)

•Clear liquids – We suggest fasting for two hours (Grade 2C).

Clear liquids include water, juices without pulp, coffee or tea without milk, and carbohydrate drinks.

•Solid food, non-clear liquids, and nonhuman milk – We suggest fasting for six hours, and eight hours for a fatty meal or meat (Grade 2C).

•Chewing gum – We suggest not chewing gum two hours prior to surgery, but we do not delay surgery for patients who continue chewing gum until surgery.

•Medications – Take with a clear liquid up to two hours prior to surgery.

For medications that must be taken orally within two hours of anesthesia, take with a sip of water.

●Special patient populations

•Standard preoperative fasting guidelines are appropriate for patients with obesity and pregnant patients who are not in labor. (See 'Patients with obesity' above and 'Pregnant patients' above.)

•Patients with gastroesophageal reflux, and patients with diabetes who have delayed gastric emptying or gastroparesis may require longer fasting times. (See 'Patients with diabetes' above and 'Patients with gastroesophageal reflux disease' above and 'Patients who have had bariatric surgery' above.)

•Optimal fasting times for patients taking glucagon type-1 receptor agonists (eg, semaglutide, liraglutide) have not been established. These drugs may slow gastric emptying and increase the risk of aspiration. Lacking evidence for optimal fasting time, we use standard fasting guidelines for patients who take these medications. We consider rapid sequence induction and intubation for those who have not held the drug prior to anesthesia or who have nausea, vomiting, or abdominal distention. (See 'Patients taking GLP-1 agonists' above.)

•For patients who are receiving enteral tube feeds, the decision to stop feeds represents a balance between the need for maximal nutritional support versus the risk of aspiration. We use the following guidelines (see 'Patients receiving enteral tube feeds' above):

-For patients undergoing abdominal surgery and those with a gastric tube who are not intubated or who have an uncuffed tracheostomy tube in place, we suggest stopping tube feeds eight hours prior to surgery (Grade 2C).

-For patients with a gastric tube and a cuffed tracheostomy tube or endotracheal tube, we decide when to stop tube feeds in consultation with the surgeon and the primary care team.

-For patients with confirmed postpyloric feeding tubes, we continue tube feeds until the patient is called for surgery.

•The benefits of oral hydration with carbohydrate drinks as part of enhanced recovery after surgery (ERAS) protocols have not been determined. Oral hydration up to two hours prior to surgery does not increase gastric residual volume or change stomach pH. (See 'Fasting in enhanced recovery after surgery protocols' above.)