Preoperative fasting guidelines

Author: Marianna Crowley, MD Section Editor: Natalie F Holt, MD, MPH Deputy Editor: Nancy A Nussmeier, MD, FAHA

Contributor Disclosures

All topics are updated as new evidence becomes available and our peer review process is complete. Literature review current through: Mar 2017. | This topic last updated: Jan 13, 2017.

INTRODUCTION — Pulmonary aspiration of gastric or oropharyngeal contents during anesthesia is a rare event, but one with significant morbidity and mortality [1]. Fasting guidelines for patients having anesthesia attempt to reduce the risk of aspiration and the severity of the pulmonary effects should aspiration occur.

Fasting guidelines are based on gastric physiology and expert opinion, as there is limited evidence that these improve outcomes [2]. Because worse outcomes may be associated with aspiration of particulate matter, of acidic contents, and of large volumes of gastric contents, guidelines aim to eliminate particulate matter and decrease the volume and acidity of gastric contents at the time of induction of anesthesia [3].

Preanesthesia fasting guidelines apply to patients having elective surgery and are intended for procedures performed under general anesthesia, regional anesthesia, and monitored anesthesia care. Aspiration may occur during all types of anesthesia in non-fasted patients, because anesthetic and sedative medications reduce or eliminate airway protective reflexes that normally prevent regurgitated gastric contents from entering the lungs [4].

The rationale and recommendations for preoperative fasting are reviewed here. Anesthetic strategies for avoidance of aspiration, the management of patients who have not fasted, and the fasting duration of patients having urgent or emergent procedures are discussed separately. (See "Rapid sequence induction and intubation (RSII) for anesthesia" and "General anesthesia: Induction".)

FASTING RECOMMENDATIONS — Recommendations that oral intake of liquids and solids be restricted for varying times prior to anesthesia aim to minimize gastric volume at the time of surgery. Various types of material empty from the stomach at different rates. While experts believe that restricting oral intake will decrease aspiration, gastric volume is a surrogate endpoint used in clinical studies because the incidence of aspiration is low.

We suggest that the following fasting intervals should be followed before induction of anesthesia:

●Clear liquids – Two hours (see 'Clear liquids' below) ●Breast milk – Four hours (see 'Other liquids' below) ●Nonhuman milk, formula, light meal – Six hours (see 'Other liquids' below and 'Solids' below) ●Fried or fatty food, or meat – Eight hours (see 'Solids' below)

Clear liquids — We require patients to consume no liquids within two hours of surgery. Patients may drink clear liquids until two hours before elective procedures requiring anesthesia or sedation. Clear liquids include water, juices without pulp, coffee or tea without milk, and carbohydrate drinks, and should not include alcohol. Protein-containing carbohydrate drinks that are administered to enhance surgical recovery should not be consumed within three hours of surgery.

Clear liquids and gastric secretions move rapidly out of the stomach; the 50 percent emptying time of water is approximately 12 minutes [5]. Glucose-containing fluids initially leave the stomach more slowly, but after 90 minutes the stomach is empty of clear liquids regardless of type [6]. Gastric residual volume averages about 25 mL in patients fasted overnight prior to surgery [7]. This is unchanged in patients who drink clear liquids, water, clear juices, coffee, tea, or carbohydrate drinks up to two hours before surgery [6,8-12]. Values for pH are also unchanged in patients drinking clear liquids.

Enhanced recovery protocols for surgery may include the administration of 300 to 400 mL of a carbohydrate drink up to two hours prior to anesthesia, which in some cases contains protein and/or lipids. One trial found gastric emptying to be unchanged when protein or lipid were added to the carbohydrate drink [13]. However, in another trial the addition of protein to the preoperative carbohydrate drink increased the time to return to baseline gastric volume from two to three hours [14]. (See "Enhanced recovery after colorectal surgery", section on 'Carbohydrate rich drink'.)

There is no evidence that restriction of the volume of clear liquids is beneficial [15]. Patients who drink carbohydrate-rich clear liquids until two hours prior to anesthesia may have less thirst, hunger, and anxiety [16], although the effect on thirst may only last 60 minutes after a drink [6].

Other liquids — Patients may not drink non-clear liquids within six hours of elective procedures requiring anesthesia or sedation. Undiluted milk is considered a solid for the purposes of preoperative fasting guidelines because it may act as a solid if it curdles in the stomach and because it contains variable amounts of protein and fat.

Non-clear liquids are felt to empty more slowly from the stomach and may leave residual particulate matter. Studies have demonstrated increased emptying times when fat is added to liquids [17,18].

The impact of suspended solid particles in liquids is less certain. A small number of trials of non-clear juices or liquids with small amounts of milk have not demonstrated delayed emptying. For example, drinking orange juice two to three hours before surgery resulted in similar gastric volumes to drinking coffee or not drinking [11]. Similarly, the addition of 50 mL of milk to 250 mL of tea did not change gastric emptying time [19]. Large amounts of milk curdle in the stomach and behave as a solid, but when diluted may behave in a manner similar to clear liquids. Expert opinion is divided on whether the addition of milk to coffee or tea precludes their identification as clear liquids [20,21].

Solids — Patients may not eat solid food (or drink milk) beginning six hours before elective procedures requiring anesthesia or sedation; the fasting interval should be increased to at least eight hours following a large or fatty meal.

Solid food takes longer than liquids to empty from the stomach. It begins emptying after a delay of about an hour, then empties in a linear fashion, with half of the solid food passing into the duodenum in about two hours [22]. However, emptying times are quite variable and depend on the volume and nutrient content of the meal. Gastric emptying is slowed by increased food weight, caloric density, and addition of fat, and is slower in females and older adults [23-27]. 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 [28]. Gastric emptying time is longer with larger meal weight, higher calorie content, and higher fat content [26]. For example, in one study, increasing meal size from 300 to 1700 grams increased the half-emptying time from 77 to 277 minutes [23].

Despite a lack of evidence for a specific interval, most patients accept and tolerate restriction of solid food, especially when liquids are allowed.

Enteral tube feeds — Patients without a cuffed endotracheal or tracheostomy tube in place should have gastric tube feeds stopped eight hours before elective procedures requiring anesthesia or sedation. In some circumstances, patients with surgically-placed post-pyloric tube feeds may have feeds continued to the time of non-abdominal surgery.

Enteral formulas often contain carbohydrates, protein, and fat, so we consider tube feeds to be a fatty meal [29]. Thus we stop gastric tube feeds eight hours prior to anesthesia for patients without either a cuffed endotracheal tube or tracheostomy tube to protect from aspiration.

It is less clear whether the patient who has the lungs protected by a cuffed endotracheal tube or tracheostomy needs to be fasted at all prior to surgery. Prolonged restriction of tube feeds may result in a catabolic state in severely ill patients. However, this must be weighed against the risk of aspiration around the endotracheal tube cuff, which occurs more frequently when these patients are placed supine, as is often required for surgery [30,31]. The surgeon, the anesthesiologist, and the primary team caring for the patient should decide whether to stop tube feeds on an individual basis, taking into account the patient’s nutritional status and other risks for aspiration. Ideally surgery should be scheduled to minimize unnecessary fasting. The patient should be transported and positioned for surgery in a head- up position, if possible.

The main advantage of post-pyloric feeding is that it may reduce the risk of gastroesophageal reflux and pneumonia [32]. We do not require that surgically-placed duodenal or jejunal tube feeds be stopped for non-abdominal surgery. Nasally-placed enteral feeding tubes lead to less certainty as to the location of the tip, and thus are treated as gastric tubes. If the patient is presenting for abdominal surgery, we also stop enteral feeding through any tube eight hours prior to surgery. (See "Enteral feeding: Gastric versus post- pyloric", section on 'Post-pyloric feeding'.)

Chewing gum — Chewing gum generates saliva and stimulates gastric secretion, so it may be considered equivalent to clear liquids. We instruct patient to stop chewing gum two hours prior to anesthesia. However, we do not delay surgery in patients who chew gum up to the time of surgery, as studies have shown either no effect on gastric volume and pH, or a small effect [33-35]. If the patient has swallowed a piece of chewing gum, we treat it as solid intake and thus delay the procedure for six hours.

Medications — Patients should take routine medications on the morning of surgery with water or a clear liquid, ideally several hours prior to the scheduled surgery. Essential medications that must be taken within two hours of surgery may include inadvertently omitted medications (eg, beta blockers, aspirin), medications on a critical schedule (eg, anti- seizure medications), or medications given as part of the anesthetic plan (eg, acetaminophen, gabapentin); these should be taken with a sip of water.

Some patients either cannot or will not take medication with a clear liquid, instead taking medication with applesauce. Often these are patients with an increased risk of aspiration related to swallowing difficulty, so fasting guidelines are of particular importance. Our approach to these patients is the following:

●Administer only medications that are absolutely necessary and cannot be given intravenously ●Administer the medication with applesauce six hours prior to the time of surgery ●Give medication that must be taken within six hours of surgery with honey, Jell-O, or a clear jelly (which may be tried on an earlier occasion to avoid anxiety or delay on the day of surgery)

SOCIETY GUIDELINES — Preoperative fasting guidelines have been developed by anesthesia societies and organizations around the world. They all allow clear liquids until two hours prior to anesthesia and restrict solid food within six hours of anesthesia [20-22,36-38]. Details may be found in the table (table 1). All rely on the physiology of gastric emptying and expert opinion, without evidence that following recommendations improves clinical outcomes.

SPECIAL POPULATIONS

Pediatric patients — Recommendations for fasting in the pediatric population are the same as for adults, with the addition of guidelines for intake of breast milk and infant formula. Children should be permitted intake of breast milk until four hours prior to surgery, and infant formula until six hours prior to surgery.

Hypoglycemia and hypovolemia are particular concerns when children are fasted, especially infants and young children [39,40]. Thus, intake of clear liquids should be encouraged up until two hours prior to surgery for children. A number of studies and a systematic review of 25 trials including 2500 children at normal risk of aspiration who were permitted clear liquids up to two hours preoperatively reported no increase in gastric volume or decrease in gastric pH compared with children who fasted for more than six hours [41-44]. In addition, those who were permitted fluids were less thirsty and hungry, more cooperative, and more comfortable.

Ingestion of clear liquids may reduce gastric volume in children. A study of gastric volume by ultrasound in children before surgery reported a small reduction in gastric antral volume two hours after a carbohydrate drink, compared with antral volume after an 8 hour fast [45].

Recommended fasting times for breast milk and formula are longer than for clear liquids because gastric emptying time for breast milk has been shown to be significantly, and variably, longer than for clear liquids, possibly because of its high fat content [46-48]. Gastric emptying time for formula has been shown to be longer than it is for breast milk. In addition, aspiration of breast milk or formula can result in significant lung injury [49,50].

Obesity — Standard fasting guidelines should be followed for preoperative obese patients. In most studies gastric emptying of both liquids and solids is not delayed in obese patients, and may be more rapid than in normal weight patients [51-55]. Other aspects of anesthetic management may need to be modified in obese patients. (See "Anesthesia for the obese patient".)

Pregnancy — Standard fasting guidelines should be followed for preoperative pregnant patients who are not in labor. Gastric emptying is normal in both obese and nonobese non- laboring pregnant women [56-58]. Gastric emptying in laboring patients is slowed [59]. Other aspects of anesthetic management may need to be modified in pregnant patients. (See "Management of the pregnant patient undergoing nonobstetric surgery".)

Diabetes — Patients with gastroparesis may benefit from a longer duration of fasting on a case by case basis. More than 50 percent of patients with longstanding type 1 or 2 diabetes mellitus have delayed gastric emptying. In one study, indigestible solid markers were retained in the stomach six hours after a carbohydrate meal in half of diabetics, though they had passed in all non-diabetics [60]. (See "Diabetic autonomic neuropathy of the gastrointestinal tract" and "Gastroparesis: Etiology, clinical manifestations, and diagnosis".)

PATIENT INSTRUCTIONS — Instructions given to patients should reflect the needs of the patient population and the scheduling system for procedures requiring anesthesia. For example, patients with language difficulties are more likely to meet the guidelines when they are given instructions regarding specific liquids (eg, ginger ale, apple juice) rather than the general category of clear liquids. Patients whose surgical time is likely to be moved ahead should be instructed to stop eating and drinking at earlier times than would be required by the scheduled surgical time.

NON-FASTED PATIENTS — When patients have not followed fasting guidelines, elective surgery may need to be delayed or rescheduled to avoid unnecessary risk. The decision to proceed or delay surgery should be made by the anesthesiologist, taking into account the type, amount, and timing of oral intake, the patient’s risk factors for delayed gastric emptying and aspiration, and the implications of delaying or rescheduling the procedure. (See "Rapid sequence induction and intubation (RSII) for anesthesia".) 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 5th to 6th 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 10th to 12th 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 topic (see "Patient education: Fasting before surgery (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Fasting guidelines for patients having anesthesia attempt to reduce the risk of aspiration and the severity of the pulmonary effects should aspiration occur. Pulmonary aspiration of gastric contents during anesthesia is a rare event, but one with significant morbidity and mortality. Oral intake of liquids and solids is generally restricted prior to anesthesia to minimize gastric volume and increase gastric pH, because worse outcomes are associated with aspiration of particulate matter, of acidic contents, and of large volumes. (See 'Introduction' above.) ●We suggest that physicians give the following instructions to patients for preoperative fasting prior to elective surgery (Grade 2C). While these are generally accepted by various societies (table 1), they are based on gastric physiology and consensus opinion rather than high-quality evidence showing a benefit on clinical outcomes. (See 'Introduction' above and 'Society guidelines' above.) •Patients may drink clear liquids until two hours before elective procedures requiring anesthesia or sedation. Clear liquids allowed until two hours preoperatively include water, juices without pulp, coffee or tea without milk, and carbohydrate drinks, and do not include alcohol. (See 'Clear liquids' above.) •Preoperative patients may be allowed to drink liquids with small amounts of protein until three hours before elective procedures requiring anesthesia or sedation, when the benefit to the patient is judged to be greater than the possible risk. (See 'Clear liquids' above.) •Patients may not eat solid food (or drink milk) beginning six hours before elective procedures requiring anesthesia or sedation; the fasting interval should be increased to at least eight hours following a heavy or fatty meal. (See 'Solids' above.) •Patients should take routine medications on the morning of surgery with water or a clear liquid, ideally several hours prior to the scheduled surgery. Medications that can be taken within two hours of surgery include inadvertently omitted essential medications (eg, beta blockers, aspirin), medications on a critical schedule (eg, anti-seizure medications), or medications given as part of the anesthetic plan (eg, acetaminophen, gabapentin); these should be taken with a sip of water. (See 'Medications' above.) ●We stop gastric tube feeds eight hours before elective procedures requiring anesthesia or sedation in patients without a cuffed endotracheal or tracheostomy tube in place. We continue feeds via surgically-placed post-pyloric tubes to the time of non- abdominal surgery. (See 'Enteral tube feeds' above.) ●Normal preoperative fasting guidelines should be used before elective surgical procedures in obese or non-laboring pregnant patients because gastric emptying is not delayed. (See 'Special populations' above.) Patients with longstanding diabetes may benefit from a longer duration of fasting on a case by case basis, because they have a high incidence of gastroparesis. (See 'Diabetes' above.) ●Patients who have not followed fasting guidelines may need elective surgery delayed or rescheduled to avoid unnecessary risk. The decision should take into account the type, amount, and timing of oral intake, the patient’s other risk factors for delayed gastric emptying and aspiration, and the implications of delaying or rescheduling the procedure. (See 'Non-fasted patients' above.) Use of UpToDate is subject to the Subscription and License Agreement.

REFERENCES

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