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Point - Counterpoint

POINT: Pediatric NPO guidelines

Christine Greco, MD, FAAP
Department of Anesthesia
Children's Hospital, Boston

Prior to 1990, fasting guidelines for children were similar to those for adults; children were fasted overnight in order to reduce the risk of pulmonary aspiration of gastric contents. Such prolonged fasting can result not only in increased irritability among children awaiting surgery, but can also be associated with a number of adverse effects such as increased chance of hypotension during induction due to preoperative hypovolemia and intraoperative hypoglycemia. Several investigators questioned the need for strict fasting practices.1-4 Studies have examined the gastric fluid volume (GFV) in children fasted according to standard guidelines compared to children allowed clear liquids until 2-3 hours before surgery.1-3 Results showed no substantial differences in GFV between the two groups, which led to changes in standard fasting guidelines to include ad lib clear liquids for 2-3 hours prior to surgery.

In a study by Ferrari et al5 preoperative fasting practices were examined among major pediatric medical centers in the US and Canada. Restricting clear liquids for 2 hours before surgery was accepted practice for the majority of pediatric anesthesia practitioners. Most clinicians agreed that a 4-hour fast was sufficient for breast feeding infants. Some practitioners (34%) considered the composition of breast milk to be equivalent to a clear liquid, others (35%) considered it equivalent to a solid, while others considered the composition to be between a clear liquid and a solid. There was little agreement regarding the appropriate fasting interval for infant formula. Fourty-three percent of institutions considered formula to be equivalent to a solid, 36% did not specify a category for formula, and 39% of institutions allowed formula 4-6 hours before surgery in children younger than 6 months of age. This study demonstrated the lack of consensus among pediatric anesthesia practitioners regarding fasting practices, particularly for formula, despite practice guidelines proposed by the ASA task force.

Controversy surrounding accepted fasting guidelines is in part based on a lack of clear understanding of the usefulness of traditional risk criteria in healthy patients undergoing elective surgery as well as insufficient investigations of gastric emptying after formula feeding. Traditional risk criteria for identifying patients at increased risk for perioperative pulmonary aspiration include GFV > 0.4 ml/kg and gastric pH < 2.5. Patients considered to be at risk for perioperative pulmonary aspiration are those with gastroesophageal reflux, decreased lower esophageal sphincter tone, increased intragastric pressure such as patients with an ileus or bowel obstruction, and trauma patients undergoing emergency surgery. Studies have shown that patients with gastroesphogeal reflux have delayed gastric emptying of solids but have normal gastric emptying of liquids which is not related to the severity of clinical symptoms.6

There is evidence to support the position that pulmonary aspiration of gastric fluid of low pH is related to the development of acid pneumonitis. Although the rationale for preoperative fasting is that low residual GFV results in a decreased risk for pulmonary aspiration among patients undergoing surgery, there is less compelling evidence to support that a GFV of > 0.4 ml/kg is required to produce clinically significant aspiration pneumonitis. In addition, up to 90% of patients will have a gastric fluid pH of 2.5 after a lengthy fast. Evidence suggests that occasionally, healthy infants will have GFV > 1 ml/kg after traditional fasting periods and increasing their length of fasting will not necessarily reduce their GFV.7,8 In a study by Litman et al, 4% of infants had a GFV of e1 ml/kg after fasting.8

Studies investigating the emptying half-life of formula from the stomach have provided support for reducing the fasting interval for formula.9-11 One study by Cavell et al, used a marker-dilution technique to determine a gastric emptying half-life of 51 minutes after formula feeding in preterm infants.9 Other studies have shown similar results. Gastric emptying in formula fed infants was estimated at 61 minutes using the 13C-octanoic acid breath test.11 Based on these studies and assuming first order kinetics, approximately 94% of the meal should leave the infant's stomach by four hours.12 Further studies however, are needed to more clearly establish gastric emptying times for different formulas based on varying fat, protein, and cow's milk composition.

Because perioperative pulmonary aspiration is a rare event, no studies have demonstrated that different fasting guidelines changes the incidence of pulmonary aspiration. Borland et al reported a 0.01% incidence of anesthesia related pulmonary aspiration in a university-affiliated pediatric hospital.13 In a retrospective review by Warner et al of 56, 138 patients younger than 18 years of age showed an overall incidence of perioperative pulmonary aspiration of 0.04%.14 There was no significant difference in the frequency of pulmonary aspiration across different age groups or ASA classification. None of the episodes of aspiration in healthy children resulted in serious respiratory morbidity and there were no deaths due to aspiration pneumonitis. The majority of patients who aspirated did so while gagging or coughing during induction or airway manipulation in the setting of absent or partial muscle relaxation. This finding suggests that anesthetic related factors in select cases may have an equally important if not more important role in the likelihood of pulmonary aspiration than the traditional risk criteria.

Cook-Sather studied the difference between GFV in infants formula fasted for 4 hours compared to the GFV in infants who were allowed clear liquids until 2 hours, but fasted 8 hours for formula and solids.12 Although there are several limitations of this study, it does provide interesting data supporting a more liberalized fasting interval for formula fed infants. The GFVs were similarly low in each group of patients (0.16 ml/kg for traditional fast group vs. 0.19 ml/kg for the liberalized fast group.) The authors did not limit the type of formula used and no single formula resulted in a particularly large GFV. However, the sample size was too small to detect differences in GFV based on the type of formula. Small amounts of residual formula were more often found in the infants fasted for < 6 hours however, residual formula was also found in infants fasted for 10 hours; the significance in relation to pulmonary aspiration risk is unclear. Both groups had low gastric pH despite different fasting intervals for formula.

There is little consensus on the optimal fasting interval for formula fed infants. The GFV required to produce aspiration pneumonitis in humans has not been clearly established. The traditional risk criteria of GFV > 0.4 ml/kg may not apply to healthy infants undergoing elective surgery. Concern regarding perioperative pulmonary aspiration has led to reluctance in reducing fasting intervals. However, pulmonary aspiration is a rare event. Studies demonstrating a relatively short gastric emptying time of formula and the lack of difference of GFV in infants allowed formula 4 hours before surgery compared to traditional guidelines provides support for liberalizing fasting guidelines for formula fed infants.

References:

1. Schreiner MS, Triebwasser A, Keon TP: Ingestion of liquids compared with preoperative fasting in pediatric outpatients. Anesthesiology 1990; 72:593-597

2. Splinter WM, Stewart JA, Muir JG: The effect of preoperative apple juice on gastric contents, thirst, and hunger in children. Can J Anaesth 1989; 36:55-58

3. Sandhar BK, Goresky GV, Maltby JR, Shaffer EA: Effect of oral liquids and ranitidine on gastric fluid volume and pH in children undergoing outpatient surgery. Anesthesiology 1989; 71:327-330

4. Cote CJ: NPO after midnight for children-A reappraisal. Anestheisology 1990; 72:589-592

5. Ferrari LR, Rooney FM, Rockoff MA: Preoperative fasting practices in pediatrics. Anesthesiology 1999; 90:978-980

6. Heyman S. Pediatric nuclear gastroenterology: evaluation of gastrointestinal reflux and gastrointestinal bleeding. In: Freeman LM, Weissman HS, eds. Nuclear medicine annual 1985; New York: Raven, 1985:133-169

7. Cook-Sathers SD, Liacouras CA, Previte JP, et al: Gastric fluid measurement by blind aspiration in paediatric patients: a gastroscopic evaluation. Can J Anaesth 1997; 44:168-172

8. Litman RS, Wu CL, Quinlivan JK: Gastric volume and pH in infants fed clear liquids and breast milk prior to surgery. Anesth Analg 1994; 79:482-485

9. Cavell B. Gastric emptying in preterm infants. Acta Paediatr Scand 1979; 68:725-730

10. Van Den Driessche M, Peeters K, Marien P, et al: Gastric emptying in formula-fed and breast-fed infants measured with the 13C-octanoic acid breath test. J Pediatr Gastroenterol Nutr 1999; 29:46-51

11. Tolia V, Kuhns L, Kauffman R. Correlation of gastric emptying at one and two hours following formula feeding. Pediatr Radiol 1993; 23:26-28

12. Cook-Sather S, Harris K, Chiavacci R, et al: A liberalized fasting guideline for formula-fed infants does not increase average gastric fluid volume before elective surgery. Anesth Analg 2003; 96:965-969

13. Borland LM, Sereika SM, Woefel SK, Saitz EW, Carillo PA, Lupin JL, Motoyama EK: Pulmonary aspiration in pediatric patients during general anesthesia: incidence and outcome. J Clin Anesth 1998; 10:95-102 Abstract

14. Warner MA, Warner ME, Warner DO, et al: Perioperative pulmonary aspiration in infants and children. Anesthesiology 1999; 90:66-71 #include ./footer_include.iphtml