“Should…[we] change pre operative fasting guidelines in neonates?”

Image: J. P. Rathmell.

In the absence of available scientific evidence, many of our clinical decisions are driven by experience and intuition at best or by dogmatism at worst. This is especially true in pediatric anesthesia practice, where therapeutic actions are rarely supported by solid scientific foundations. This frustrating situation has, nevertheless, one fortuitous consequence: It can foster the kind of clinical research where important questions with potentially direct implications to patient care can be answered with relatively little effort.

In this issue of the journal, Lee et al. provide us with new data that nicely exemplify this possibility.1  The authors focus on gastric emptying times in neonates after formula feeding, an as yet unexplored but important question in the context of preoperative fasting in this population. Using serial ultrasound scans of the gastric antral cross-sectional area, before and every 15 min after formula feeding in 46 newborns aged 0 to 5 days, the authors found that gastric emptying time ranged from 45 to 150 min in the overall study group with no clinically meaningful differences between male and female newborns or those delivered by vaginal versus cesarean routes.

This simple but elegant and straightforward observational study provides us with new physiologic information of therapeutical relevance in the context of preoperative fasting in neonates. Indeed, little is known about the temporal course of gastric emptying in the very young. It is, therefore, not entirely surprising that both the American and European perioperative fasting guidelines recommend a safety limit of 6 h of preoperative fasting in formula-fed neonates and infants.2,3  These current recommendations are solely expert opinion–based and acknowledge the lack of sufficient knowledge in the field. Nevertheless, there are several studies outside the field of perioperative medicine suggesting that gastric emptying after formula feeding is meaningfully faster than the recommended 6-h period in preterm4  and term neonates5  as well as in infants.6  These earlier observations primarily focus on gastric half-emptying time and convincingly demonstrate that a substantial portion of the ingested formula volume is cleared from the stomach in 1 h after feeding. One may reasonably argue that gastric half-emptying time may not be a clinically useful endpoint in the context of preoperative fasting, and more needs to be known about the kinetics of gastric emptying. In line with this demand, a recent study assessed the time course of gastric emptying in preterm neonates using repeated ultrasonographic assessment of the gastric antral cross-sectional area.7  These observations reveal that, after formula feeding, gastric volume returns to prefeeding values in within an average of 199 min (range, 175 to 225 min), well under the 6-h period recommended by current guidelines. In the study by Lee et al.,1  using the same ultrasound methodology as Beck et al.,7  gastric emptying times are even faster (range, 45 to 150 min), reflecting the fact that gastric emptying is faster in healthy term compared to preterm neonates.5 

What shall we do with these new data? Should they prompt us to change preoperative fasting guidelines in neonates? It is generally assumed that a single study, especially that of an observational nature, should not lead us to change practice. However, in light of the previously accumulated circumstantial evidence, partially cited here, the results from Lee et al. are not really new and unexpected. Rather, they confirm what many of us involved in the perioperative care of neonates already know and intuitively apply. In line with this, some national guidelines already advocate for decreased fasting times in neonates after formula feeding.8,9  When the option of changing guidelines and practice is on the table, one has to consider the pros and cons these changes may apply. In the case of neonatal perioperative fasting, the benefits of reducing fasting times outweigh the potential risks. Indeed, prolonged fasting in the very young can trigger a variety of physiologic/pathophysiological changes such as discomfort, dehydration, intraoperative hypotension, hypoglycemia, and increased lipolysis.10  It is also known that, due to uncertainties related to the operating room schedule, pediatric fasting times can far exceed the official recommendations, which, especially in neonates, can further lead to iatrogenic morbidity.11  The one single potential risk associated with decreased fasting times is pulmonary aspiration. However, in this context, one has to remember that the incidence of pulmonary aspiration in children is very low,10  and we do not have any available data on the incidence and consequences of pulmonary aspiration in neonates. We also know that, in experienced hands, neonates with “full stomach” such as pyloric stenosis can be safely anesthetized without rapid sequence induction.12  These latter observations together with the data of Lee et al., showing gastric emptying in less than 150 min in all their study subjects, strongly suggest that we can safely anesthetize healthy term neonates 3 h after formula feeding. Whether the same is true for preterm infants where gastric physiology may be different needs to be further investigated.

What kind of studies do we need to further strengthen the evidence on the safety of reduced fasting times in neonates? In their article, Lee et al. propose a potential research agenda for future studies in this regard. They argue for the need of a large trial to determine the incidence of rare pulmonary events. While such a randomized trial, comparing the 3-h-long and the 6-h-long formula fasting regimens in terms of pulmonary aspiration, is indeed interesting, it could hardly ever be conducted even in a multicentric international setting since the incidence of clinically relevant pulmonary aspiration is very low (0.02%) and, most importantly, it is reportedly not higher in fasted than in nonfasted children.10  Another line of research put forward by the authors would be to compare indicators such as blood glucose levels and preoperative fasting times between the two fasting regimen groups. Despite the fact that this kind of research could provide us with additional arguments in favor of reduced fasting times, it will not answer the question of safety related to these fasting regimens since there is no established relationship between these indicators and clinically relevant outcome in neonates in the perioperative setting. These difficulties mean that, other than performing some additional confirmatory studies on gastric emptying, it will be very difficult to conduct research further proving the safety of reduced preoperative fasting times in neonatal populations. Hence, the real question is whether we are comfortable to reduce fasting times in the very young based on already available evidence, or if, by being overly cautious and fearful of aspiration, we ignore these reassuring data and continue to apply the 6-h fasting rule in healthy neonates the same way we do in adults. Those who are regularly involved with the perioperative care of these young patients probably know the answer already.

Dr. Vutskits is an editor of Anesthesiology.

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