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To the Editor:
We agree with the comment suggesting that conducting sensitivity analyses will be important for determining the validity of our results. We defined the cut-off time point for a prolonged hospital stay as 8 h from the end of anesthesia until discharge. We discussed the reason for selecting this cut-off point in our article  as follows: “This was because ambulatory surgeries were always scheduled for morning in our institution. The expected time of the end of anesthesia was between 9 and 11 a.m.; therefore, 8 h, not 6 h, after the end of anesthesia would fall outside of daytime working hours.” We have performed sensitivity analyses with cut-off points of either 7 or 9 h; these cut-off points would be meaningful because 7 or 9 h after the end of anesthesia would also fall outside of daytime working hours. With respect to the intraoperative fluid volume, similar results were obtained [odds ratio (95% confidence interval; CI): 0.82 (0.69–0.99) and 0.62 (0.44–0.88) for cut-off points of 7 and 9 h, respectively]. Regarding the caudal block, the trend in the results was consistent [odds ratio (CI): 0.71 (0.40–1.25) and 0.29 (0.10–0.89) for cut-off points of 7 and 9 h, respectively] but the 95% CI became wider when the cut-off time was 7 h. We argue that the consistent results of these sensitivity analyses support the validity of our results.
At our hospital, the attending nurse and anesthesiologist independently assessed all patients using a PADSS instrument. Therefore, we think that the bias introduced by unstandardized discharge criteria was minimal.
We agree with the comment that the discharge time was very different from that in other studies. As discussed in our article, clinical variations between institutions, such as the surgery type, indications for ambulatory surgery, or discharge criteria, may preclude the application of our results to other institutions. Therefore, our results should be considered as hypothesis-generative findings, and future studies will be needed to investigate whether the potentially modifiable factors in our study, such as intraoperative fluid volume or the type of regional block, could prevent unnecessary extended hospitalization periods and admissions for pediatric patients.
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Conflict of interest
The author(s) declare that they have no competing interests.