Comment on ‘Optimized preoperative fasting times decrease ketone body concentration and stabilize mean arterial blood pressure during induction of anesthesia in children younger than 36 months: a prospective observational cohort study’

SIR–We read with interest this paper regarding optimization of preoperative fasting in a pediatric cohort (1). We would like to congratulate the authors and provide some constructive contributions. This study analyses techniques for optimization of preoperative fasting times to minimize discomfort and postoperative complications often caused by inappropriate fasting. The study concludes that a new protocol (OPT) significantly improves fasting times, MAP values (mean arterial pressure), and ketone body levels compared to a previously studied group (OLD). These metabolic parameter outcomes were measured after induction of anesthesia. However, postoperative clinical parameters (cognition, vomiting, pain, and discharge time) would have also been impactful in measuring the effect of the techniques. Furthermore, we cannot ignore the different fluid losses and shifts that occur with different surgeries. These impact metabolic imbalances at the end of a case, hence future studies should take account of this too; with parameters measured postoperatively as well as postinduction. An audit carried out in 2013 (2) found improvements using similar techniques as this study, showing these are effective in improving adherence. We do however question which intervention is best and importantly most easily achievable and we would welcome a survey of staff at this center in Hanover to further elucidate this. Individual techniques could be investigated by a multisite study. Patients would be randomized for surgery to different sites each with an individual optimization technique, but we appreciate location is limited by patient preference, logistics, and funding. The OLD and OPT cohorts were matched effectively; however, half of the OLD cohort was lost and we feel a more robust analysis, with increased statistical power, would have included a larger OPT cohort. This study investigated a population with a large age range (0–36 months), encompassing significant differences in physiology and feeding. We would welcome data looking at more specific age subgroups. For instance, the authors presented an improvement in MAP across the OPT cohort overall despite different blood pressure targets below 1 year against those 2–3 years old. Mean MAP values were significantly lower in the OLD cohort, however still above a hypotension defining value of 40 mmHg. While we accept this statistical significance (50.3 vs 55.2 mmHg), we question whether a change of 5 mmHg is clinically relevant in this age range. Furthermore, significantly fewer cases of hypotension are presented in the OPT cohort. We agree that 40 mmHg is hypotensive in children below 3 years of age; however, we were unable to find coherent evidence to justify it as a definitive cut-off with clinical implications. Ketone levels have been shown to correlate, unsurprisingly, with reduced oral intake and vomiting in a pediatric population; however, there was no correlation with illness severity (3). In this study regarding optimization, mean ketone levels were shown to be significantly higher in the OLD cohort, however this was still considered just within normal boundaries (0.6 mmol l ) (4). Importantly, the range presented within the OLD cohort did not extend beyond 1.3 mmol l . This is within a value of 1.5 mmol l 1 which is considered a possible keto-acidotic boundary (4) used in NHS trust guidelines. In light of this, we question the clinical significance of this reported reduction in the OPT cohort. We feel the suggestions made are very valuable but have their own challenges with local implementation hence we would value input from other centers who have tried to implement these. While this research paper addresses an important question in search of the holygrail of pediatric fasting times, we look forward to more data regarding clinical relevance and successful application of the recommendations to other hospitals.