Preoperative and Postoperative Fasting in Children

Preoperative and Postoperative Fasting in Children

PEDIATRIC ANESTHESIA 0031-3955/94 $0.00 + .20 PREOPERATIVE AND POSTOPERATIVE FASTING IN CHILDREN Mark S. Schreiner, MD An appreciation of the basic...

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PEDIATRIC ANESTHESIA

0031-3955/94 $0.00 + .20

PREOPERATIVE AND POSTOPERATIVE FASTING IN CHILDREN Mark S. Schreiner, MD

An appreciation of the basic physiology of gastric emptying and resultant clinical trials has shortened the duration of the preoperative fast for elective surgery. Shortening the mandatory fasting interval prior to anesthesia stands as one of the most humane advances in the perioperative care of children. One might question why pediatricians should focus on this issue because this area is usually outside their realm. There are at least three reasons why pediatricians should concern themselves with the duration of the preoperative fast. First, in many settings pediatricians and family practitioners participate in the preoperative and postoperative care of children. Second, anesthesiologists who care primarily for adult patients may not be as aware of the recent developments in this area as anesthesiologists who care exclusively for children. In this situation, pediatricians can be powerful advocates for children and can become a force for overcoming obstacles and promoting change within their local communities. Last, primary care givers frequently supervise conscious sedation for invasive or noninvasive procedures. Conscious sedation may unexpectedly progress to unconscious sedation. Unconscious sedation is akin to general anesthesia without protection of the airway, placing the patient at risk of aspiration of gastric fluid contents. Given this possibility, fasting guidelines prior to conscious sedation should be the same as those for general anesthesia.

BACKGROUND Aspiration pneumonia produced by inhalation of actively or passively regurgitated gastric contents remains a dreaded complication of general anesthesia.

From the Department of Anesthesiology and Critical Care Medicine, The Children's Hospital of Philadelphia; and University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania

PEDIATRIC CLINICS OF NORTH AMERICA VOLUME 41 • NUMBER 1 • FEBRUARY 1994

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Although reported first in 1848 as a complication of general anesthesia, Mendelson receives the credit for describing the pathophysiology of the acid aspiration syndrome nearly 100 years later, in 1946Y In an attempt to reduce the risk of aspiration pneumonia in low-risk patients scheduled for elective surgery, a period of preoperative fasting commonly lasted from 8 to 12 hours prior to the induction of anesthesia. Patients deemed to have a higher than ordinary risk are considered to have a "full stomach" despite a prolonged preoperative fast. Conditions associated with a high risk of aspiration of gastric fluid contents during general anesthesia follow: Pregnancy Gastrointestinal obstruction Emergency surgery History of vomiting during induction of anesthesia Esophageal disease Difficult airway Obesity Oversedation Increased intracranial pressure Systemic infection/ sepsis Measures gradually introduced into anesthetic practice that have reduced the risk of pulmonary aspiration of gastric fluid in these high-risk patients include: the use of tracheal intubation instead of a face mask during the conduct of general anesthesia, the awake/sedated approach to tracheal intubation, the use of cuffed tracheal tubes, emptying of the stomach with a nasogastric tube prior to induction of anesthesia, the implementation of the rapid sequence induction (use of a rapid onset barbiturate with succinylcholine and tracheal intubation), and the application of cricoid pressure to prevent regurgitation during induction (Sellick's maneuver). The revised fasting guidelines do not apply to these patients. Risk Factors for Aspiration Pneumonia

Numerous investigators have attempted to define the volume and composition of fluid necessary to produce severe or fatal aspiration pneumonia in animal models. Roberts and Shirley21 alluded to unpublished work in rhesus monkeys which suggested that "0.4 ml./kg. is the maximum acid aspirate that does not produce significant changes in the lung." They then defined patients to be at risk if their gastric fluid contents exceeded 25 mL (or 0.4 mL/kg) with a pH less than or equal to 2.5. Studies in rats have shown a high mortality with aspiration of acidic fluid. s On the other hand, Raidoo and colleagues20 have recently investigated the effect of aspiration volume of homogenized, acidified (pH 1) gastric fluid on the severity of aspiration pneumonia in rhesus monkeys. All of the animals in the 0.4 or 0.6 mL/kg groups survived, whereas 1 of 6 in the 0.8 mL/ kg group and 3 of 6 in the 1.0 mL/kg group died. It is impossible to know with certainty the minimum volume that a given individual must aspirate before developing severe respiratory symptoms, but based on the more recent work in primates, 0.8 mL/kg of inhaled acidic fluid is a reasonable estimate. Gastric Emptying

A new appreciation of the physiology of gastric emptying has been instrumental in revising the policies for preoperative fasting. The rate of emptying of

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the gastric contents depends on the volume and the constituents of the meal.' Solid food empties linearly over time. The mean time required for the stomach to half empty (T1fz) equaled 77, 146, and 277 minutes for 300, 900, and 1692 gm meals.!S The emptying T1fz for a filling meal (1692 gm) averaged 277 ± 147 minutes with a range of 130 to 638 minutes. Clear liquids empty exponentially with a T1fz that is considerably faster than for solids. Clear liquids, however, are not all equivalent; the rate of emptying depends on composition. Glucose, sorbitol, and KCl slow gastric emptying but sodium bicarbonate and NaCl enhance emptying provided the concentration remains less than 200 mosmoles/L.3 At an osmolarity greater than 200 mosmoles/L, sodium bicarbonate and NaCl decrease the rate of gastric emptying rather than increase it. The rate of gastric emptying after a liquid meal has been well studied in adultsY After drinking 750 mL of a pulp-free orange drink, the mean gastric emptying T1fz ranged between 10 ± 7 and 20 ± 11 minutes. The fastest T1fz for an individual subject was 2.9 minutes and the slowest T1fz was 41.6 minutes. Two hours (approximately five Tl/zS) after a clear liquid drink, the stomachs of most individuals will contain none of the recently consumed beverage. Even individuals with the slowest emptying rates will retain only 10% or less of the original liquid within their stomachs after 2 hours. It is impossible to explain to an infant the importance of fasting prior to surgery. Because babies prefer to drink milk rather than apple juice or sugar water, from the baby's perspective, milk would be the ideal preoperative meal. Unfortunately, few studies have examined gastric emptying after a milk meal. Tomomasa and colleagues3! compared gastroduodenal motility differences between breast milk and an infant formula with a nearly identical macro nutrient composition. The appearance of phase 3 of the migrating myoelectric complex was used by Tomomasa to signal the return to the fasting state. Three hours after the test meal, 75% of infants fed breast milk had entered the fasting state compared with only 17% of the formula-fed infants. Using ultrasonagraphy to assess gastric emptying, Marzio and colleagues!O reported that a liquid meal consisting of 500 mL of saline resulted in 50% emptying in only 15 ± 4 minutes and 100% emptying in 30 ± 5 minutes. In comparison, a 500 mL liquid meal of cow's milk emptied by 50% in 67 ± 17 minutes and 100% in 166 ± 30 minutes. Breast milk clearly empties faster than formula but slower than clear liquids. Cow's milk and formula appear to empty somewhat faster than solids.

Preoperative Factors and Gastric Fluid Volume

Stress Cote and colleagues2 examined the hypothesis that preoperative stress would affect residual gastric fluid volume and pH in children. Children were randomized into three groups consisting of outpatients, inpatients, and patients who had undergone multiple operations. There were no differences between the groups, nor was there a difference in the residual gastric fluid volume between children who appeared anxious (mean 0.7 ± 0.1 mL/kg) and those who did not (mean 0.83 ± 0.2 mL/kg). Residual gastric fluid averaged 0.78 ± 0.1 mL/kg with a pH of 1.45 ± 0.3 for the entire group. In one patient, the residual gastric fluid volume totaled 4.72 mL/kg. Based on these data, it seems that a large percentage of children will have residual gastric fluid sufficient in volume and

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acidity to produce severe aspiration pneumonitis at the time of induction of anesthesia. Illness or trauma greatly delays gastric emptying. Preanesthetic Medication

Anesthesiologists commonly use preanesthetic medications which often consist of an anticholinergic, an opioid, and a sedative used alone or in combination. Although opioids slow gastric emptying and anticholinergics increase the rapidity of emptying, it is not clear that the effects are clinically relevant. Glycopyrrolate is reported to reduce residual gastric fluid volume when administered by intramuscular injection 1 hour prior to induction. 22 Intramuscular injection, however, is rarely used at the present time to administer preanesthetic medications making glycopyrrolate use uncommon. Pentobarbital and morphine do not increase residual gastric fluid volume compared with placebo. 22 Manchikanti and colleagues9 found no advantage or disadvantage to administering meperidine, diazepam, and hydoxyzine in a variety of combinations compared with no preanesthetic medication. Spontaneous Reflux of Gastric Contents

The essential sequence of events necessary to produce aspiration pneumonitis includes: gastric contents capable of producing lung damage, regurgitation of gastric contents, and aspiration of gastric contents. Regurgitation may occur secondary to lower esophageal sphincter incompetence or active vomiting. Modern anesthetics have minimized the incidence of active vomiting on induction, but silent passive regurgitation occurs with high frequency. The exact volume of gastric fluid needed to produce spontaneous regurgitation in anesthetized or sedated healthy patients is unknown, but some extrapolation from data obtained in animals is possible. Plourde and Hardt9 estimated the minimal gastric fluid volume needed to produce spontaneous regurgitation in cats (considered to be a good model for LES function in humans). The volume of fluid in the stomach required to produce regurgitation averaged 23.5 ± 12.0 mL/kg (range 8 to 41 mL/kg) in awake cats and 20.8 ± 7.8 mL/kg (range 12 to 38 mL/kg) in anesthetized cats. These volumes far exceed the 0.8 mL/kg (instilled directly into the trachea) required to produce severe aspiration pneumonia. Are Children at Risk for Aspiration Pneumonia?

Because large volumes of acidic, residual gastric fluid are common in children at the time of induction of anesthesia, are children at particular risk of aspiration pneumonia? The answer appears to be a qualified yes. Olsson and colleagues17 retrospectively reviewed all the anesthetic records in which aspiration occurred as a complication of anesthesia or surgery. Confirmed aspiration during anesthesia occurred in 87 of the 185,358 cases (4.7 per 10,000). Four patients (1/46,340 anesthetics) died related to their pulmonary aspiration. The incidence of aspiration in children between the ages of 0 and 9 years was nearly three times higher (8.6/10,000) than in young adults (2.9/10,000). None of the children died, and the high incidence was largely attributed to the practice of tracheal intubation without the benefit of muscle relaxant and lack of experienced staff to assist with emergency cases.

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The circumstances leading to pulmonary aspiration in children in the study of Olsson and colleagues17 are potentially avoidable. The authors' experience at The Children's Hospital of Philadelphia has failed to document a high incidence of significant aspiration pneumonia (Thomas P. Keon, personal communication, 1993). In contrast to the practices noted by Olsson and colleagues,17 the author prefers to use a nondepolarizing muscle relaxant to facilitate tracheal intubation. Over the past 5 years in more than 50,000 patients no inpatient has required admission to the intensive care unit, and no day surgical patient has required hospital admission as the result of aspiration pneumonia. Significant aspiration pneumonia seems to be a relatively rare complication of modern anesthetic practice for both adults and children. SHORTENING THE PREOPERATIVE FASTING INTERVAL Adults

Given the physiology of gastric emptying and the apparent low risk of pulmonary aspiration, clinical investigators began to question the necessity for a prolonged preoperative fast.>4 Maltby and colleagues6 examined the effect of a small drink 2.5 hours prior to the induction of anesthesia. After an overnight fast, women undergoing first trimester induced abortion were randomized to fast until induction of anesthesia or to drink 150 mL of water an average of 2.5 hours prior to induction. The residual gastric fluid volume in those who drank water averaged 18 ± 15 mL compared with 27 ± 19 mL in the control group. The mean pH was not statistically different between the two groups (1.75 and 1.92 units respectively). The administration of ranitidine halved the residual gastric fluid volume for both groups and increased the pH. Numerous studies subsequently replicated the essential features of this investigation and further concluded that black coffee, pulp-free orange juice, and opioid-atropine preanesthetic medication administered 1 hour prior to induction do not affect gastric emptying.4, 7, 9, 12, 30

Children

There is no reason to expect that gastric emptying is significantly different in children compared with adults. Because children suffer psychologically more than adults during a prolonged fast, it was inevitable that investigators would eventually examine the effect of oral liquids on residual gastric fluid volume in children. Splinter and colleagues24 fasted 80 children ages 5 to 10 years for an average of 15 ± 2 hours and then allowed half to drink 3 mL/kg of apple juice 2.5 hours prior to the induction of anesthesia. Gastric fluid volume in the children allowed to drink averaged 0.24 ± 0.31 mL/kg compared with 0.43 ± 0.46 mL/ kg (significantly different). The children who were allowed to drink were less thirsty and less hungry. Sandhar and colleagues23 compared gastric fluid volume in fasted children with a group allowed to drink 5 mL/kg of juice 2 to 3 hours prior to induction. All patients drank 1 mL of the indicator phenolsulfonphthalein. There were no differences in the gastric fluid volume between the two groups and phenolsulfonphthalein was not recovered from any patient fasted for at least 2.25 hours. In a study at The Children's Hospital of Philadelphia, the authors randomized 53 of 121 healthy children aged 1 to 18 years into a group allowed to drink

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ad lib clear liquids until 2 hours prior to surgery (the last drink was limited to 8 ounces), whereas the remaining children were fasted according to the prevailing protocol,28 Those younger than 5 years of age could drink until 6 hours prior to induction and those older than 5 years until 8 hours. Although the required fasting interval was only 6 or 8 hours, the mean fast lasted 13.5 ± 3.1 hours with the longest fast lasting 23 hours. A prolonged preoperative fast has been consistently observed in other reports. 23,24 Apparently most families find it difficult to awaken their children in the middle of the night simply for the purposes of administering a drink. The authors' study differed from prior investigations in two important ways: (1) parents were responsible for regulating the child's intake while at home rather than in the controlled environment of the hospital, and (2) an unlimited quantity of clear fluid was allowed. The two groups had comparable residual gastric fluid volumes and gastric fluid pH. Additional studies have demonstrated that children with congenital cardiac disease scheduled for cardiac surgery,'6 adolescents,>6 and children allowed unlimited clear liquids27 are not at increased risk when allowed free access to clear liquids (Table 1). Children, or parents of children who are allowed to drink, rate themselves or their children to be less thirsty, less hungry, less irritable, more comfortable, and to have better tolerated the preoperative waiting period than fasted children.'6, 24, 28 The range of residual gastric fluid at the time of induction is quite wide. Cote and colleagues2 reported values between 0.11 mL/kg to 4.72 mL/kg and the values reported by Splinter and colleagues25 ranged between 0.01 to 4.08 mLI kg. Figure 1 shows a frequency distribution based on the data from two previously published reports.'6 ,28 Although most children have gastric fluid volume less than 2 mL/kg at the time of the induction of anesthesia, occasional children will exceed this limit. It is clear from the evidence that clear liquids consumed 2 to 3 hours prior to the induction of anesthesia have no adverse effect on residual gastric fluid volume in healthy children and therefore do not increase the risk of pulmonary

0.25 0.5 0.75

1

1.25 1.5 1.75

2

2.5

3

3.5

4

4.5

Gastric Fluid Volume (ml/kg) Figure 1. The distribution of residual gastric fluid volume for 206 children. Approximately 96% of patients have gastric fluid volumes < 2.0 mUkg at the time of induction of anesthesia. (Data from Nicolson et al'6 and Schreiner et a1. 2B )

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Table 1. EFFECT OF UNLIMITED CLEAR LIQUIDS 2 TO 4 HOURS PRIOR TO INDUCTION ON GASTRIC FLUID VOLUME

Reference Schreiner"8 Splinter"7 Nicolson'·

Group Control Study Control Study Control Study

Age

7.3 5.9 5.7 5.6 3.3 3.1

± ± ± ± ± ±

4.6 5 2.5 2.7 3.9 4.1

NPO Interval (hours)

13.5 2.6 13.9 3.3 10.4 2.5

± ± ± ± ± ±

3.1 0.7 2.5 0.9 4.3 0.5

Volume of Fluid unlimited" unlimited unlimited

Gastric Fluid Volume (mUkg)

0.6 0.4 0.4 0.3 0.4 0.6

± ± ± ± ± ±

0.5 0.5 0.4 0.3 0.6 0.9

·Last drink limited to 8 ounces

aspiration. Since 1989, more than 25,000 children admitted through the Day Surgical Unit have been anesthetized at The Children's Hospital of Philadelphia after a minimum of 2 hours of fasting. The authors are unaware of any complications as a result of this shortened fast. Preoperative Fasting Guidelines

Prior to the adoption of a 2 hour fasting interval, violation of feeding guidelines usually resulted in either a prolonged delay or cancellation of surgery. The most common violation at the present time is an error in the timing of the last drink of clear liquids, resulting in only a short delay. If an unanticipated delay in the elective surgical schedule arises, a drink of clear fluids or a popsicle often makes the wait more tolerable. Explicit written instructions for families are essential if violations of the feeding policies are to be avoided. Without written directions, parents of a hungry, thirsty child are as likely to feed the child a bowl of cereal as give him or her apple juice. The consequences of these two meals are quite different. An example of preoperative instructions for day surgery and medicine patients is presented in Table 2. To reduce the risk of aspiration pneumonia in patients who are believed to be at increased risk, a single dose of oral ranitidine 2 mg/kg administered 2 to 3 hours prior to induction will significantly reduce gastric fluid volume and increase pH.23 It must be emphasized that these guidelines apply to healthy children for elective surgery. Emergencies following trauma, such as fractures, and systemic illness all delay gastric emptying and require caution. It also should be emphasized that clear liquids do not mean anything else. Liberal guidelines must not be construed to mean hamburgers, milkshakes, and french fries! FASTING AFTER SURGERY Effect of Requiring Patients to Drink Prior to Discharge

Vomiting is the most common postoperative complication of anesthesia and surgery. IS Vomiting is unpleasant and if severe enough, may require an unplanned hospital admission following outpatient surgery. Vomiting is noted in

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Table 2. PREOPERATIVE FEEDING INSTRUCTIONS

For your child's safety, it is very important that you follow these instructions carefully. If these instructions are not followed, your child's operation or procedure may be canceled or delayed. 1. At 8 p.m: the evening before surgery Stop All Food including Solid food, candy,t and chewing gum Milk, milk products, and formulas+ Orange juice and juice containing pulp 2. Breast feeding may continue until 3 hours§ before the time you are to arrive at the hospital. 3. Clear Fluids may be continued until 2 hours§ before the time you are to arrive at the hospital. 4. Clear fluids include Clear Broth Water Pedialyte Apple Juice Ice popsicles Clear juice drinks Plain Jell-O ·Many hospitals use midnight rather than 8 p.m. for the beginning of the NPO period. tHard sucking candy is probably of little concem and a variety of opinions exist regarding the significance of gum chewing. :j:The duration for fasting after formulas is uncertain at present and shorter intervals may be appropriate. §It takes a minimum of 30 minutes to process a day surgery patient at CHOP, but parents occcasionally make subtraction errors when the instructions are not stated using integers.

the hospital records and by follow-up interview in 14% to 18% of day surgery patients at The Children's Hospital of Philadelphia. The actual incidence is likely to be 25% to 100% higher based on clinical studies that have focused on this one complication. Ensuring that children are capable of retaining liquids prior to discharge from the hospital has been the standard approach to postoperative management. The basis for this approach was to prevent the need for readmission to the hospital secondary to dehydration. Some clinicians have questioned the necessity or even the wisdom of requiring children to drink immediately after a surgical procedure.1 A prospective randomized trial conducted recently tested the hypothesis that mandatory drinking prior to discharge from the hospital increased the incidence of vomiting. 29 Patients randomized to the mandatory drinking group (n = 464) were required to drink and retain at least 2 ounces of clear liquid before they were considered ready for discharge from the hospital. Patients randomized to the elective drinking group (n = 525) were allowed to drink clear liquids if they wished but had no requirement to drink. All patients received the equivalent of 8 hours maintenance fluid during surgery. The incidence of vomiting for the two groups was identical in the postanesthetic care unit (no patients drank in that location) and following discharge from the hospital (26% versus 27% incidence). In the day surgery predischarge area, only 14% elective drinkers experienced one or more episodes of vomiting compared with 23% of the mandatory drinkers. This significant reduction in postoperative emesis occurred even though nearly 80% of the elective drinkers chose to drink. Mandatory drinkers had a higher incidence of emesis and stayed 20% longer in the predischarge area. Nauseated children prefer not to drink. With the requirement to drink prior to discharge eliminated, the incidence of vomiting diminished. Children vomit more frequently after discharge from the hospital than during the hospital stay independent of whether they drank clear liquids in the hospital. Retaining clear

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liquids prior to discharge therefore did not prevent severe vomiting and dehydration after discharge. At The Children's Hospital of Philadelphia, we have processed 15,000 day surgery patients without requiring them to drink prior to discharge. Aside from children undergoing myringotomy tube placement, all patients receive a minimum of the equivalent of 8 hours maintenance fluid intravenously during their hospital stay. Nurses and families allow each child to decide when he or she is ready to drink. In 1992, only 29 of approximately 7000 (0.4%) day surgery patients required unanticipated admission because of severe vomiting (T.P. Keon, MD, personal communication, May 1993). Twenty of the 27 had undergone tonsillectomy and adenoidectomy surgery which is a well-recognized cause of severe vomiting. We attribute the low admission rate to the decreased incidence of vomiting in our day surgical unit, adequate hydration prior to discharge, and a deemphasis on the importance of postoperative drinking, dehydration, and vomiting. CONCLUSION

Until early 1990 perioperative oral fluid management for children could be summarized as "Starve Preop: Feed Postop." Recent advances have reversed the conventional wisdom and now allow children to drink clear liquids up unti12 hours prior to surgery and to fast after surgery until they want to eat. The pattern of gastric emptying of milk, formula, and breast milk needs further investigation. Better information might allow anesthesiologists to minimize the fasting interval for the youngest patients. With a higher percentage of patients undergoing surgery as surgical outpatients, control of postoperative vomiting is more important than ever. Anesthetic techniques that minimize postoperative emesis are evolving. Better techniques and pharmacologic agents to provide postoperative analgesia without the emetic side effects of opioids are still needed. References 1. Berry FA: The child in the recovery room. In Berry FA (ed): Anesthetic Management of Difficult and Routine Pediatric Patients. New York, Churchill Livingston, 1989, pp 619645

2. Cote CJ, Goudsouzian NG, Liu LM, et al: Assessment of risk factors related to the acid aspiration syndrome in pediatric patients - gastric pH and residual volume. Anesthesiology 56:70, 1982 3. Hunt IN: Some properties of the alimentary osmoreceptor mechanism. J Physiol 132:267,1956 4. Hutchinson A, Maltby JR, Reid CRG: Gastric fluid volume and pH in elective inpatients. Part I: coffee or orange juice versus ovemight fast. Can J Anaesth 35:12,1988 5. James CF, Modell JH, Gibbs CP, et al: Pulmonary aspiration - Effect of volume and pH in the rat. Anesth Analg 63:665,1984 6. Maltby JR, Sutherland AD, Sale JP, et al: Preoperative oral fluids: Is a five-hour fast justified prior to elective surgery? Anesth Analg 65:1112,1986 7. Maltby JR, Koehli N, Shaffer EA: Gastric fluid volume, pH, and emptying in elective inpatients. Influences of narcotic-atropine premedication, oral fluid, and ranitidine. Can J Anaesth 35:562, 1988 8. Maltby JR, Reid CRG, Hutchinson A: Gastric fluid volume and pH in elective inpatients. Part II: coffee or orange juice and ranitidine. Can J Anaesth 35:16, 1988 9. Manchikanti L, Canella MG, Hohlbein LJ, et al: Assessment of effect of various modes of premedication on acid aspiration risk factors in outpatient surgery. Anesth Analg 66:81,1987

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10. Marzio L, Giacobbe A, Conoscitore P, et al: Evaluation of the use of ultrasonagraphy in the study of liquid gastric emptying. Am J Gastroenterology 84:496,1989 11. McClelland GR, Sutton JA: Epigastric impedance: A non-invasive method for the assessment of gastric emptying and motility. Gut 26:607,1985 12. McGrady EM, Macdonald AG: Effect of the preoperative administration of water on gastric volume and pH. Br J Anaesth 60:803, 1988 13. Mendleson CL: The acid aspiration of gastric contents into the lungs during obstetric anesthesia. Am J Obstet GynecoI52:191, 1946 14. Miller M, Wishart HY, Nimmo WS: Gastric contents at induction of anaesthesia: Is a 4hour fast necessary? Br J Anaesth 55:1185,1983 15. Moore JG, Christian PE, Coleman RE: Gastric emptying of varying meal weight and composition in man: Evaluation by dual liquid- and solid-phase isotopic method. Dig Dis Sci 26:16, 1981 16. Nicolson SC, Dorsey AT, Schreiner MS: Shortened preanesthetic fasting interval in pediatric cardiac surgical patients. Anesth Analg 74:694,1992 17. Olsson GL, Hallen B, Hambraeus-Jonzon K: Aspiration during anaesthesia: a computeraided study of 185358 anaesthetics. Acta Anaesth Scand 30:84, 1986 18. Patel RI, Hannallah RS: Anesthetic complications following pediatric ambulatory surgery: A 3-yr study. Anesthesiology 69:1009,1988 19. Plourde G, Hardy JF: Aspiration pneumonia: Assessing the risk of regurgitation in the cat. Can Anaesth Soc J 33:345,1986 20. Raidoo DM, Rocke DA, Brock-Utne JG, et al: Critical volume for pulmonary acid aspiration: Reappraisal in a primate model. Br J Anaesth 65:248, 1990 21. Roberts RB, Shirley MA: Reducing the risk of acid aspiration during cesarean section. Anesth Analg 53:859,1974 22. Salem MR, Wong AY, Mani M, et al: Premedicant drugs and gastric juice pH and volume in pediatric patients. Anesthesiology 44:216, 1976 23. Sandhar BK, Goresky GV, Maltby JR, et al: Effect of oral liquids and ranitidine on gastric fluid volume and pH in children undergoing outpatient surgery. Anesthesiology 71:327,1989 24. Splinter WM, Stewart JA, Muir JG: The effect of preoperative apple juice on gastric contents, thirst, and hunger in children. Can J Anaesth 36:55,1989 25. Splinter WM, Stewart JA, Muir JG: Large volumes of apple juice preoperatively do not affect gastric fluid pH and volume in children. Can J Anaesth 37:36,1990 26. Splinter WM, Schneider ME, Schaefer JD: Unrestricted clear fluids 3-hours before anesthesia is safe for adolescents. Anesth Analg 70:5387,1990 27. Splinter WM, Schaefer JD: Clear fluids three hours before surgery do not affect the gastric fluid contents of children. Can J Anaesth 37:498, 1990 28. Schreiner MS, Triebwasser A, Keon TP: Ingestion of liquids compared to preoperative fasting in pediatric outpatients. Anesthesiology 72:593,1990 29. Schreiner MS, Nicolson SC, Martin T, et al: Should children drink before discharge from Day Surgery? Anesthesiology 76:528-533,1992 30. Sutherland AD, Maltby JR, Sale JP, et al: The effect of preoperative oral fluid and ranitidine on gastric fluid volume and pH. Can J Anaesth 34:117,1987 31. Tomomasa T, Hyman PE, Itoh K, et al: Gastroduodenal motility in neonates: Response to human milk compared with cow's milk formula. Pediatrics 80:434,1987

Address rerpint requests to Mark S. Schreiner, MD Department of Anesthesiology and Critical Care Medicine The Children's Hospital of Philadelphia 34th and Civic Center Boulevard Philadelphia, PA 19104-4399