Point - Counterpoint
Counterpoint: Formula before surgery: Is there evidence for a new consensus on pediatric NPO guidelines?
Helen V. Lauro, M.D.
Clinical Assistant Professor
Department of Anesthesiology
SUNY-Downstate/The Long Island College Hospital
Brooklyn, New York
Traditionally anesthesiologists are taught the NPO after midnight rule (Latin: Nulla per os or "nothing by mouth") from their first day of residency. Under this rule, children were lumped together with adults, and fasted for all solids including milk and clears, for eight hours prior to surgery, because of concern for aspiration. The period of time that a child can safely fast has been reconsidered in the past years. Now we must ask if there is compelling evidence for a new consensus on pediatric NPO guidelines, regarding infant formula.
Most anesthesiologists are well educated about the detrimental aspects of prolonged fasting in infants and children. These include hypovolemia, hypoglycemia and increased irritability. The benefits of allowing four ounces of clear liquids 2-3 hours before surgery include decreased acidity and gastric residual volume (GRV), increased gastric emptying, and flexibility in the operating room schedule should procedures be moved earlier in the day. Studies by Splinter et al 1 found no significant difference in GRV or pH in children who were allowed to have clear liquids until two to three hours before surgery, compared with controls with standard preoperative fasting.
Current ASA practice guidelines for preoperative fasting
Many institutions practice age-specific NPO guidelines in view of the positive correlation of age with GRV. This is because aspiration is a real risk in the pediatric population. Studies from the Mayo Clinic reveal the incidence of aspiration is similar in adults (3.1 per 10,000) 6 and children (3.8 per 10,000) 7. A retrospective study in the United States of 50,880 anesthetics suggested that the incidence of aspiration in children was more frequent (10.2 per 10,000).8 Our age-specific institutional protocol is a four-hour fast from milk and solids for infants younger than 6 months of age; a six-hour fast from milk and solids for children 6-36 months of age; and an eight-hour fast from milk and solids for children older than 36 months of age.9
Breast milk is not considered a complete solid. Depending on the institution, breast milk is treated as a clear liquid (23%), between a clear and formula (36%), a solid (34%), or as formula (7%). Part of the reason is that there is little data examining absorption of breast milk in healthy infants. Some institutions accept a four-hour restriction for breast milk.4 Fortification of breast milk does not appear to delay gastric emptying compared to unfortified breast milk. A blinded crossover study of 22 low-birth weight infants using sonography to measure gastric antral cross-sectional area showed no significant difference in gastric emptying with the presence of a fortifier.10
There is no consensus on how to treat infant formula and sparse investigation of gastric emptying after formula feeding.11 Formula varies in composition (whey-predominant mimicking breast milk or casein-predominant mimicking cow's milk) osmolarity, pH, fat and protein content, and all of these can affect GRV. In a study of 201 infants using sulfur-colloid Tc and cinegastroscintigraphy, the rate of emptying was fastest with breast milk and slowest with cow's milk, with formula in between. One-hundred-twenty minutes after ingestion, the percentage gastric residual activity was 19 ± 16 % (mean ± SD) for breast milk, 25 ± 18 % for whey-formula, 38 ± 21 % for casein-formula, and 48 ± 19 % for cow's milk.12 A review of physiological studies 9 suggests that casein based milk requires at least 5 hours to leave the stomach. Using the 13C-octanoic acid breath test13 it was found that gastric emptying in 29 infants was significantly slower with formula milk than breast milk. Clinical practice by anesthesiologists concerning treatment of formula is very variable. According to Ferrari et al,4 formula is treated as a solid by 43%, between a clear and solid 20%. In children under 6 months of age, 39% of institutions permit formula 4-6 hours before anesthesia. A recent postal survey of practice of 149 anesthetists in the United Kingdom revealed that 51% of respondents practiced a 4 hour fast for neonates on formula feeds, while 37% practiced a 6 hour fast for neonates. For infants on formula feeds, 37% of anesthetists were evenly divided between 4 hours and 6 hours.14
To date there is little evidence to support liberalizing fasting guidelines for infant formula. In support of allowing infant formula as liquid rather than solid, a recent prospective randomized study 15 attempts to challenge the current ASA guidelines, and concludes fasting may be liberalized for formula, after a 4-6 hour fast. In their study 97 ASA I or II infants were randomized into traditional and liberalized groups. The traditional group was allowed no solids/milk or formula for 8 hours prior to surgery, but clears up to 2 hours before surgery. The liberalized group was allowed to ingest formula 4-6 hours before surgery. Oral atropine was given to all participants in this study. Thirty infants had prolonged fasts, and thus were excluded. The protocol analysis was for 67 infants with an age range of 0.7 to 10.5 months. Contrary to the expectations of the study, infant irritability and hunger and parental satisfaction were not significantly affected by allowing formula up to four hours before surgery.
The study is valuable and intriguing, but has several important limitations. First they have a small sample size of insufficient power, which the authors admit. They state they determined a sample size of 140 subjects (69 per group) to be sufficient to detect a difference of a = 0.05 with 80% power. Second, the broad age range further impairs the power of the study, as the controversial age range is 6-12 months. Third, many formulas were utilized in the study, and no attempt was made to randomize patients to specific formula groups. This has relevance because some formulas have cow milk components, which are more dangerous because of their propensity to form solid curds in gastric juice. The authors admit this and further state that because of the variety of formulas used, the sample size for each was too small to note GRV differences based on formula type. Fourth, the use of atropine somewhat may confound the absolute GRV as the authors state that atropine may reduce GRV. This is because of its properties as a muscarinic antagonist; gastric secretions would decrease to a greater extent than it may have decreased GI motility leaving smaller GRV. However, in practice, atropine is not routinely given by all pediatric anesthesiologists, and absolute GRV may be higher than the practitioner anticipated. Fifth, it is important to realize that comprehension of fasting guidelines may be more complicated for parents to understand as there may be confusion with cow milk/formula/breast milk, with deleterious consequences. Many parents have difficulty understanding what "clears" mean. Many hospitals do not have the resources of a nurse to confirm feeding diary entries with parents.
The evidence for liberalization of formula is limited and does not support revising pediatric NPO guidelines. While it is a meritorious idea, a randomized controlled study in a more specific age range of 6-12 months with a clearly defined fasting interval needs to be specifically addressed with different formulas, a control group and with and without atropine. Anesthesiologists should be cautious about modifying their clinical practice without further supportive evidence. Preoperative anticholinergics do not obviate the risks of aspiration. According to the ASA task force, published evidence is equivocal regarding the use of anticholinergics to decrease gastric volume or acidity, and is not associated with improved outcome related to pulmonary aspiration. Further studies and discussion by the pediatric anesthesia community is warranted.
References: 1. Splinter, W.M. et al. Large volumes of apple juice preoperatively do not affect gastric pH and volume in children. Can J Anaesth 1990; 37(1): 36-9.
2. American Society of Anesthesiologists. Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration- a report by the American Society of Anesthesiologists. Park Ridge, IL; 1999.
3. Emerson, B. M. et al. Preoperative fasting for paediatric anaesthesia. A survey of current practice. Anaesthesia 1998; 53(4):326-30.
4. Ferrari, L. R, et al. Preoperative fasting practices in pediatrics. Anesthesiology 1999; 90(4): 978-80.
5. Green, C. R. Et al. Preoperative fasting time: is the traditional policy changing? Results of a national survey. Anesth Analg 1996; 83(1): 123-8.
6. Warner, M. A. et al. Clinical significance of pulmonary aspiration during the perioperative period. Anesthesiology 1993;78(1):56-62.
7. Warner, M. A. et al. Perioperative pulmonary aspiration in infants and children. Anesthesiology 1999;90(1):66-71.
8. Borland, L.M. et al. Pulmonary aspiration in pediatric patients during general anesthesia: incidence and outcome. J Clin Anesth 1998; 10(2):95-102.
9. Lauro, H. Cutting edge pediatric anesthesia for the outpatient. Same Day Surgery Reports Supplement May 2002: 1-7.
10. McClure R.J. et al. Effect of fortifying breast milk on gastric emptying. Arch Dis Child Fetal Neonatal Ed 1996;74(1): F60-2.
11. Tobia, V. et al. Correlation of gastric emptying at one and two hours following formula feeding. Pediatr Radiol 1993; 23(1): 26-8.
12. Ng, A. et al. Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice. Anesth Analg 2001;93(2):494-513.
13. Van Den Driessche M et al. Gastric emptying in formula-fed and breast-fed infants measured with the 13-C octanoic acid breath test. J Pediatr Gastroenterol Nutr 1999; 29(1):46-51.
14. Bliss, A. Pre-operative starvation-have we changed our views since Emerson, Wrigley and Newton? Paed Anesthesia 2002;12:829-30.
15. Cook-Sather, S. D. et al. A liberalized fasting guideline for formula-fed infants does not increase average gastric fluid volume before elective surgery. Anesth Analg 2003; 96(4): 965-9.
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