To the Editor:—
We read with interest the case report by Kawabata et al. 1of pulmonary aspiration on induction of anesthesia in an infant fed formula 4.5 h before surgery. We have long been proponents of liberalized fasting guidelines for clear liquids and, more recently, for infant formula.2,3For infants younger than 6 months of age, expert opinion has been equally divided as to 4 h or 6 h formula fast requirements.4,5The liberalization of formula fasting to 4 h, as outlined by Dr. Cotê6and at least temporarily adopted by Dr. Kawabata's institution, is a practice we continue to support in healthy infants younger than 6 months old. We recognize that there are very limited data to support either the safety or the hazard of such a practice.
The bases of our position are both theoretical and experiential. Gastric fluid volume (GFV), used as a surrogate marker for pulmonary aspiration risk, is small and not significantly different if measured in infants fasted for either 4 h or 6 h.3Since July 2001 we have employed a preoperative fasting directive at The Children's Hospital of Philadelphia permitting healthy infants formula feeds 4 h before surgery. Using the CompuRecord anesthesia record system (Phillips Medical Systems, Andover, MA) to search for events of “pulmonary aspiration related to anesthesia care,” one of our mandatory quality assurance markers, we reviewed all pediatric cases conducted at our institution from 9/01/98 to 5/31/04. Within this period we compared pulmonary aspiration events in two 34-month epochs, one before and one after the liberalization of infant formula fasting from 6 h to 4 h, and found no increased incidence (table 1). In fact, for reasons that remain unclear, there was a 10-fold reduction in overall incidence of pulmonary aspiration from the first epoch to the second (Fisher exact test P = 0.0002.) With regard to patients <6 months of age, however, there were no documented aspiration events in any of the 9,266 infants cared for in the past 6 yr. Our experience is consonant with that of others.7It is important to note that although we allowed healthy infants formula at 4 h before procedures from July 2001 on, we have no data as to how many infants actually fed between 4 h and 6 h before induction of anesthesia. Lastly, from a more global perspective, if we were to assume that the 50% of North American and European practitioners surveyed by Emerson et al. 4and Ferrari et al. 5allow a 4-h fast and have not found an increased incidence of pulmonary aspiration, then the evidence for the safety of this practice may be growing.
As for the case presented by Kawabata et al. , she appeared to be a healthy infant who came for elective surgery of the lip. Height and weight appeared normal, consistent with normal gastrointestinal function and nutritional status. Nevertheless, undiagnosed chronic and subclinical acute disorders may have caused gastrointestinal dysmotility that could have contributed to the aspiration described. Both total feed volume (260 ml within 1 h) and formula characteristics (formula derived from cow milk) may have contributed to the event as well. A 120-ml feed might be more typical and appropriate 4 h before anesthesia and surgery in a young infant. In our fasting study, feed volumes averaged 120–150 ml.3Human milk and whey-based formula are emptied faster than casein-based formula and cow's milk.8There is insufficient data to state with certainty that one formula is safer than another, but given the slower emptying times for the latter, a case can be made for either avoiding them or prolonging the fast.
Kawabata et al. misquoted our GFV study3by stating “…9% of formula-fed infants who fasted for 4 h had undigested traces of formula in their gastric content.”1In fact, 9% (9/97) of all of our subjects had traces of residual formula. Evidence of formula was found in 13% of subjects fasted for <6 h and in 3% of those fasted for ≥6 h. Interestingly, one 8.5-month-old infant who fasted for 10 h still had a white tinge to the recovered gastric aspirate. We believe that these white-tinged residua associated with small GFV and pH not different from traditional fasts do not significantly increase pulmonary aspiration risk. Given the limited data, however, practitioners who wish to reduce the risk of even trace amounts of formula in the stomach may feel more comfortable recommending a 6-h fast. Finally, GFV remains an imperfect surrogate marker for pulmonary aspiration.9Small GFVs do not preclude vomiting and aspiration of upper small bowel contents via retrograde giant contractions and no study has examined small bowel emptying time as it relates to formula feeds.
The central issue is that pulmonary aspiration of gastric contents is a rare event.7Mortality or significant morbidity associated with pulmonary aspiration is exceedingly rare. To carefully measure the impact of various fasting regimens on even uncomplicated pulmonary aspiration, randomized, controlled trials would require sample sizes in excess of 30,000.3In the past 6 yr, overall patient volume at The Children's Hospital of Philadelphia exceeds this number but not in the infant subpopulation of interest. No matter how fasting guidelines are designed, the risk of pulmonary aspiration of gastrointestinal contents, even in fasted healthy infants, will never be zero. None of this diminishes the importance of the case report. When events are rare, the case report may be the only way of tracking emerging patterns and trends that will enhance our understanding and permit best practice to continue to evolve.
* The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania. firstname.lastname@example.org