Preoperative fasting in children and infants

INTRODUCTION — Children and adults are routinely required to fast before procedures that require sedation or general anesthesia, with the goal of reducing the risk of aspiration of gastric contents and the severity of the pulmonary effects should aspiration occur. This topic will discuss the rationale and basis for preoperative fasting, effects of fasting on infants and children, and the existing guidelines.

Preoperative fasting guidelines for adults and anesthetic strategies for avoidance of aspiration are discussed separately. (See "Preoperative fasting in adults" and "Rapid sequence induction and intubation (RSII) for anesthesia".)

RATIONALE FOR PREOPERATIVE FASTING — Sedation and anesthesia reduce or eliminate protective cough reflexes, unlike natural sleep. Thus, aspiration of stomach contents that are passively regurgitated or vomited into the oropharynx may be more likely during sedation or anesthesia. Aspiration during anesthesia is a rare event, but it can cause morbidity or rarely mortality [1-4]. Because worse outcomes may be associated with aspiration of particulate matter, of acidic contents, and of large volumes of gastric contents, goals for preoperative fasting are to eliminate particulate matter and decrease the volume and acidity of gastric contents at the time of induction of anesthesia.

Preoperative fasting is based on gastric physiology and expert opinion, as there is limited evidence that fasting improves outcomes. There is consensus that solid food should be avoided for prolonged periods to allow clearance from the stomach (ie, six to eight hours or more), because aspiration of food particles can be immediately life threatening.

Gastric volume is a surrogate endpoint used in most clinical studies. While experts believe that restricting oral intake will decrease aspiration, there is not a known gastric volume that either eliminates risk or places a particular child at undue risk [5-7]. In most studies of the effects of fasting on the risk of aspiration, "at risk," has been defined as a gastric volume of >0.4 mL/kg and a pH of <2.5, but this definition is based on animal and laboratory studies [6-8], without clear relevance to humans. Studies using gastric ultrasound have found that residual gastric volume may be as high as 1.5 mL/kg in appropriately fasted patients [9-11]. Based on these results, some experts have redefined "at risk" as >1.5 mL/kg [12,13]. Nevertheless, skillful anesthetic management may be more important than fasting for prevention of aspiration [14].

INCIDENCE AND OUTCOME OF ASPIRATION DURING ANESTHESIA — Aspiration of gastric contents during anesthesia is rare. The reported incidence of aspiration of gastric contents during anesthesia in children is between 2 and 10 per 10,000 anesthetics, with a low incidence of serious outcomes [2,15-22]. The low incidence of aspiration may reflect anesthetic practices, including preoperative fasting and airway management techniques, which are used to minimize the chance of aspiration. Examples of studies of perioperative aspiration include the following:

●In one prospective database study including 56,138 patients younger than 18 years of age who underwent general anesthesia between 1985 and 1997, aspiration occurred in 24 patients (4 per 10,000 anesthetics) [16]. Children who underwent emergency procedures were more likely to aspirate than those who underwent elective procedures (1/373 versus 1/4544). Nine patients developed signs of pulmonary aspiration within two hours of aspiration, five required intensive care and respiratory support, and three required prolonged mechanical ventilation. No patient died as result of aspiration.

●A prospective multicenter survey study of 118,371 pediatric anesthetics in the United Kingdom over one year between 2010 and 2011 reported that aspiration occurred in 2 per 10,000 anesthetics [23]. Of the 24 patients who aspirated, 16 became symptomatic, and 5 of those required postoperative mechanical ventilation for 5 hours to 10 days. No patient died as a result of aspiration.

●The Anaesthesia PRactice In Children Observational Trial (APRICOT) study was a prospective, observational study of critical events in children <15 years of age who underwent anesthesia in 261 centers throughout Europe in 2014 and 2015 [17]. The incidence of aspiration was 9.3 per 10,000 cases; 57 percent of the children who aspirated recovered uneventfully, 38 percent became hypoxemic, and 3 percent required prolonged intubation. Emergency surgery was the only identified risk factor for aspiration (relative risk [RR] 8.43, 95% CI 1.97-36.10).

EFFECTS OF FASTING — Unnecessary fasting should be avoided, especially for infants and very young children. The desire to have an empty stomach during induction of anesthesia must be balanced against the deleterious effects of prolonged fasting, including patient discomfort, hypovolemia, lipolysis, and ketogenesis [24], with low normal blood glucose [24-26].

Most of the effects of fasting for solids can be reduced or eliminated by allowing or encouraging ingestion of glucose-containing liquids until two hours prior to anesthesia. In one cohort study including 100 children <36 months of age who underwent general anesthesia, the effects of fasting were studied before and after institution of a protocol designed to encourage feeding and reduce any fasting beyond what was required by guidelines [27]. The children in the optimized fasting group had shorter fasting times (mean 362 versus 507 minutes), higher mean arterial blood pressure after induction of anesthesia (mean 55.2 versus 50.3 mmHg), lower ketone levels (mean 0.2 versus 0.6 mmol/L) and a lower incidence of hypotension after induction of anesthesia (mean arterial pressure 55.2 versus 50.3), compared with children in the control group. Details for induction of anesthesia were not provided. In another retrospective study of approximately 15,500 children who underwent general anesthesia without preinduction venous access, the duration of preoperative fasting was not clearly related to the incidence of postinduction hypotension [28]. While longer duration of fasting for clear liquids was associated overall with increased postinduction hypotension, the association was not linear; fasting for four to eight hours was associated with increased risk of hypotension, compared with fasting for less than four hours, whereas the risk of hypotension associated with fasting for 8 to 12 hours was similar to fasting for less than four hours.

Fasting for liquids beyond two hours does not reduce the residual gastric volume in healthy children [25]. (See 'Clear liquids' below.)

GASTRIC EMPTYING AND VOLUME — The volume of stomach contents depends on salivary secretions (1 mL/kg/hour), gastric secretions (0.6 to 3 mL/kg/hour), oral intake, and gastric emptying. Multiple factors in the perioperative period can alter the normal rate of gastric emptying and residual gastric volumes in children, including stress, anxiety, temperature, age, metabolic activity, infection, and medications (eg, opioids) [29,30].

Gastric emptying may be markedly slowed in children with trauma. A study of gastric aspirate volumes in 110 children aged 1 to 14 years undergoing surgery for trauma found that longer fasting time and longer consumption to injury time were associated with smaller residual gastric volume, but 49 percent of children had volumes greater than 0.4 mL/kg after eight hours of fasting [31]. Hunger was not a reliable indicator of low gastric volume, as 5 of 41 children who claimed to be hungry had residual gastric solids and one of them had a gastric volume of nearly 7 mL/kg.

Solids — For most patients without risk factors for delayed stomach emptying, a fast for six hours after a light meal is appropriate, and should be adequate to ensure a stomach empty of solids. A longer fast is required for larger, high-fat meals. This is consistent with preoperative fasting guidelines from most anesthesia societies, though the 2022 European Society of Anesthesiology Guideline for Preoperative Fasting in Children makes a weak recommendation to allow a light breakfast up until four hours prior to anesthesia (table 1) [14].

Gastric emptying of solids relies on gastric motility, which is slow and unpredictable, and depends on the food composition and the calorie content of the meal. Food with high lipid content empties slowest, carbohydrates next, and proteins fastest [32].

The rate of gastric emptying is controlled by the energy content of the food, and in adults occurs at approximately 200 kcal/hour [33]. In adults, a high calorific or filling meal (patient feels satisfied) may require at least nine hours for stomach emptying, whereas a small (300 g) meal will be absorbed in three to four hours [34]. In one of the few studies of the emptying of solids in children, 13 of 32 children who ingested a biscuit two to four hours before surgery had food particles in gastric aspirate after induction of anesthesia [32].

Milk products — Children may ingest three types of milk products: animal (cow's or goat's) milk, formula products, and human breast milk. Milk forms a curd when it meets the acid environment of the stomach and, therefore, becomes a semi-solid. Breast milk empties from the stomach faster than most formulas and non-human milk, but all require at least two hours, and possibly longer, for the stomach to empty. Most fasting guidelines specify at least a three- or four-hour fast for breast milk and four to six hours for non-human milk or formula (table 1). (See 'Fasting guidelines at the author's institution' below.)

Breast milk is easily absorbed by neonates and infants early after birth as it has a lower lipid content at this stage [35]. It has a physiologic pH of between 6.7 and 7.4, a physiologic osmolarity of 286, and a variable ratio of casein to whey depending on the time from delivery until cessation of breastfeeding by the mother. The ratio of casein to whey changes over time, and is the reason that breast milk absorption slows in older infants. Thus, the required fasting time for breast milk for young infants may be shorter [35]. (See 'Fasting guidelines at the author's institution' below.)

Formula composition is highly variable; for preoperative fasting, formulas have generally been considered similar to animal milk. However, a number of institutions and anesthesia organizations make a distinction between animal milk and formula, and some have reduced fasting time for formula, particularly for young infants (see 'Fasting guidelines at the author's institution' below). Reduced fasting time is supported by a study of gastric emptying of formula in 46 healthy neonates, using serial gastric ultrasound [36]. After ingesting an average of 30 mL of formula, gastric volume returned to within 10 percent of baseline in 45 to 150 minutes, with a mean of 92.9 minutes, substantially less than the currently recommended fasting times.

However, a number of other studies have evaluated the gastric emptying of milk products in infants; the pharmacokinetics of absorption of animal milk and formula are quite variable. Examples of relevant studies include the following:

●In studies of gastric emptying in preterm infants [30] and in infants aged four weeks to six months [37] using a marker dilution technique, half-emptying times for formula were almost twice as long as half-emptying times for breast milk. In both studies, most infants' stomachs were empty by two hours, but several had large residual gastric volumes.

●In another study, gastric emptying of breast milk, three types of formula, and cow's milk was measured using radioisotope labelling in 110 healthy infants after 100 to 200 mL feeds [38]. At two hours, gastric residual content, as a proportion of the initial meal, was 18 percent after breast milk, 16 to 39 percent with various formulas, and 55 percent with cow's milk.

●In a prospective blinded study that compared healthy infants less than one year of age who were breastfed or fed clear liquid approximately two hours before surgery, gastric fluid was sampled with an orogastric tube after endotracheal intubation [39]. All of the breastfed infants who had enough gastric fluid aspirated for analysis had gastric volumes ≥0.4 mL/kg, and 29 percent of those had gastric volumes ≥1 mL/kg. Seventeen percent of infants fed clear liquids had a gastric volume ≥0.4 mL/kg, and 7 percent had a gastric volume ≥1 mL/kg. This study was stopped early because of the large percentage of breastfed babies with large gastric residual volume.

Clear liquids — Increasingly, recommended fasting intervals for liquids are being reduced, with some institutions allowing clear liquids almost immediately prior to surgery [20]. Many fasting guidelines allow clear liquids up to one hour prior to surgery for children.

Clear liquids (ie, liquids that are transparent and nonparticulate) generally empty very rapidly from the stomach, independently of motility, and follow first order or exponential clearance. The half-emptying time for water in the stomach is 13 minutes. The fastest clearing fluids are pH neutral, iso-osmolar with no calories. Thus, normal saline clears faster than 10 percent dextrose [40]. In a randomized trial using gastric ultrasound to compare gastric emptying of 5 ml/kg of 5% glucose versus a carbohydrate rich clear liquid (14.5% glucose) in 11 volunteers aged three to seven years, gastric volume reached pre-ingestion baseline at 30 minutes in those who drank 5% glucose, and at 90 minutes after ingestion of carbohydrate-rich liquid [41].

However, gastric volume after ingestion of liquids varies widely [39,42]. A gastroscopy study of 285 children aged 1 month to 18 years allowed a variety of clear fluids up to two hours before the procedure reported gastric volumes of 0 to 15 mL/kg, but no correlation with fasting duration [43]. In another study, ultrasound scanning of the gastric antrum was used to evaluate gastric emptying in 48 healthy volunteer children who drank apple juice, a clear high-protein drink, or 2 percent milk [42]. There was wide variability in stomach emptying among subjects and drinks, and no difference among the groups, with the stomach empty at 3 to 3.5 hours for all three drinks.

Many studies have shown no benefit in fasting for clear liquids longer than two hours before a procedure [19,20,41,43-47]. Examples include the following:

●A 2009 meta-analysis of 25 randomized trials that compared various fasting regimens in healthy children <19 years of age found that children who were allowed intake of clear fluids up to two hours prior to anesthesia had no greater gastric volumes and had similar gastric pH compared with children who fasted for longer periods [19]. When possible to evaluate, children who were permitted fluids were less hungry and thirsty, more comfortable, and better behaved, though there were no differences in these outcomes among fasting times from two to four hours.

●In a subsequent study, in 131 children who were randomly assigned to clear liquid fasting for one or two hours prior to anesthesia, there was no difference in gastric residual volumes or gastric pH [48].

●A large multi-institutional prospective observational study of approximately 12,100 children who underwent general anesthesia found that the incidence of regurgitation or aspiration was similar in children with clear liquid fasting times of one to two hours, two to four hours, and >4 hours (0.24 percent, 0.37 percent, and 0.36 percent, respectively) [22]. There were no cases of mortality, prolonged hospital stay, unplanned intensive care unit admission, antibiotic therapy, or prolonged postoperative ventilation.

However, children who consume liquids in the hour prior to anesthesia or large volumes of liquid close to the time of surgery may have significant gastric residual volumes at the time of induction. The gastric volume of liquid that increases risk of aspiration remains unknown, though historically, 0.4 mL/kg has been used to define increased risk. (See 'Rationale for preoperative fasting' above.)

●In a study that compared liberal versus standard preoperative fasting regimens for liquids in healthy children, 15 percent of children who had free access to clear liquids up until premedication had gastric residual volumes >2 mL/kg at the time of intubation, with a mean fasting time of 32 minutes [49]. Children who consumed >3 mL/kg of liquid at the time of last fluid intake also had high residual gastric volumes.

●In one randomized trial, 227 children drank 3 mL/kg (maximum 150 mL) of apple juice and were assessed with gastric ultrasound one hour versus two hours later [50]. Median gastric fluid volume at one hour was double the volume at two hours (0.61 mL/kg versus 0.32 mL/kg). Antral grading (assessment of emptying, higher with fluid present) was higher at one hour. There were no aspiration events.

●In a small prospective observational study of 24 children who were scheduled for general anesthesia, gastric ultrasound was used to assess emptying time after ingestion of water or fruit juice [51]. Gastric emptying time was <1 hour in children who consumed <5 mL/kg of either liquid, but was incomplete at one hour in children who consumed >5 mL/kg of liquid. There was no difference between the gastric emptying times of water and fruit juice.

Chewing gum — The effect of chewing gum on gastric residual volume is unclear, but likely to be clinically insignificant; this issue has been studied in adults. Chewing gum may increase gastric volume in fasted patients [52], presumably because of increased salivary or gastric secretions, but could also decrease gastric volume by increasing gastric motility [53]. A meta-analysis of four randomized controlled trials including 287 patients found that chewing gum before induction of anesthesia increased gastric volume by a small, likely clinically insignificant amount (mean difference 0.21 mL/kg), without a change in pH of stomach contents [54]. A subsequent study reported no difference in gastric emptying of water in patients randomly assigned to chew gum after ingestion or not [55].

In addition to the effects of chewing on gastric residual volume, swallowed chewing gum should be considered a solid for the purposes of preoperative fasting. Children may not admit to having swallowed chewing gum, or may keep gum hidden against the hard palate to avoid detection. Thus, we consider chewing gum a solid and our guidelines prohibit gum chewing for six hours prior to surgery.

PREOPERATIVE GASTRIC ULTRASOUND — As point of care ultrasound is increasingly used in the operating room for a variety of purposes, gastric ultrasound has been used in clinical trials to assess gastric volume and contents in infants, children [9,56-58], and adults [10,12,59]. Gastric ultrasound is noninvasive, and in experienced hands can be performed quickly.

Ultrasound assessment of gastric contents and volume has been shown to be particularly beneficial in emergency patients or children having elective surgery whom have breached fasting guidelines [12,14].

However, similar to other methods for assessing gastric residual volume, results have not been correlated with the risk of aspiration, and further study is required before using gastric ultrasound to guide clinical decisions. Preoperative gastric ultrasound is discussed more fully separately. (See "Overview of perioperative uses of ultrasound", section on 'Gastric ultrasound'.)

FASTING GUIDELINES AT THE AUTHOR'S INSTITUTION — 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 are as follows, applicable to infants and children of all ages:

●Clear liquids – one hour (up to 3 mL/kg)

●Breast milk – three hours

●Formula or cow's milk – four hours

●Solids (light meal) – six hours

Preoperative fasting guidelines or consensus statements have been developed by anesthesia societies and organizations around the world (table 1) [60-68]. All rely on the physiology of gastric emptying and expert opinion, without evidence that following recommendations improves clinical outcomes.

Regardless of institution-specific guidelines, every effort should be made to avoid prolonged unplanned fasting because of schedule delays, especially in very young children, and clear fluid intake should be encouraged, within the bounds of the established guidelines.

SPECIAL POPULATIONS — Standard fasting guidelines apply to healthy children without risk factors for abnormal gastric emptying or aspiration. Fasting instructions and modifications of anesthetic technique for patients with comorbidities (eg, diabetes) and/or gastrointestinal disorders (eg, gastroesophageal reflux, gastric outlet, or bowel obstruction) that may decrease or prevent gastric emptying should be individualized.

In children [69] and adults with obesity gastric emptying times are similar to patients without obesity. (See "Preoperative fasting in adults", section on 'Patients with obesity'.)

Traumatic injury slows gastric emptying in an unpredictable way. Both the time between last oral intake and injury, and the duration of fasting after injury may affect gastric volume, but a substantial number of children will have a large gastric residual volume even after prolonged fasting. This was illustrated by a study in which gastric aspirate volume was measured after endotracheal intubation in 110 pediatric trauma patients [31]. A longer time between last oral intake and injury, and a longer fasting period after injury, were both associated with overall lower gastric volume, However, 50 percent of children who were fasted eight hours or longer and 30 percent of children who were injured three or more hours after last oral intake had gastric volumes >0.4 mL/kg. Hunger was not a reliable indicator for an empty stomach.

SOCIETY GUIDELINE 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" and "Society guideline links: Pediatric anesthesia".)

SUMMARY AND RECOMMENDATIONS

●Rationale for preoperative fasting – Children are required to fast before anesthesia to reduce the risk of aspiration of stomach contents and the severity of pulmonary effects should aspiration occur. However, there is limited evidence that fasting reduces the risk of aspiration, and no known gastric volume that either confers or eliminates risk. (See 'Rationale for preoperative fasting' above.)

Aspiration during anesthesia is a rare event, with a low incidence of serious outcomes, but prolonged mechanical ventilation and the need for intensive care may occur. (See 'Incidence and outcome of aspiration during anesthesia' above.)

●Avoid unnecessary fasting – Unnecessary fasting should be avoided to reduce the risk of hypovolemia, ketogenesis, hunger, and thirst, especially in very young children. Most of the effects of fasting for solids can be reduced or eliminated by allowing or encouraging ingestion of glucose-containing liquids until two hours prior to anesthesia. (See 'Effects of fasting' above.)

●Physiology of stomach emptying – The volume of stomach contents depends on secretions, oral intake, and stomach emptying.

•Gastric emptying for solids is slow and variable, and depends on the food composition. A small meal may empty within three to four hours, whereas large, high-fat meals may require nine hours or more. (See 'Solids' above.)

•Milk products (ie, breast milk, formula, animal milk) require at least two hours for stomach emptying. (See 'Milk products' above.)

•Clear liquids empty rapidly from the stomach. Fasting for liquids beyond two hours does not reduce the residual gastric volume in healthy children. (See 'Clear liquids' above.)

•The effects of preoperative gum chewing on gastric volume are unclear, but likely to be clinically insignificant. However, we consider chewing gum a solid, since children may not admit to having swallowed chewing gum, or may keep gum hidden against the hard palate to avoid detection. (See 'Chewing gum' above.)

●Fasting guidelines – Preoperative fasting guidelines have been developed by anesthesia societies around the world (table 1). Institutional guidelines are often developed with multidisciplinary consensus. Our institutional guidelines are as follows, applicable to infants and children of all ages: (see 'Fasting guidelines at the author's institution' above)

•Clear liquids – one hour (up to 3 mL/kg)

•Breast milk – three hours

•Formula or cow's milk – four hours

•Solid food (light meal – six hours

●Special populations – Fasting and the management of anesthesia for children at high risk of aspiration and/or abnormal stomach emptying (eg, children with diabetes, gastroesophageal reflux, bowel or gastric outlet obstruction, trauma) should be individualized. (See 'Special populations' above.)