Reply to Liqi et al.

Dear Editor,

We thank Dr Liqi [1] for interest in and constructive comments on our study [2].

This study aimed to elucidate the effects of cardiopulmonary bypass (CPB) on the gut microbiota and intestinal tract and to evaluate the potential benefits of probiotic administration in alleviating these effects.

First, on the topic of the sample size, as Dr Liqi [1] pointed out, our sample size was insufficient to definitively demonstrate the efficacy of probiotics. As noted in the limitations [2], collecting a statistically sufficient sample size at a single centre was difficult.

Next, we would respond to why we did not conduct a long-term follow-up. First, previous studies have shown that CPB-induced intestinal damage typically normalizes within a few days postoperatively [3]. Our 7-day postoperative follow-up was sufficient to evaluate this damage. Second, the results obtained at long-term follow-up are influenced by a variety of factors in the life of each patient after discharge that are not related to the effects of CPB, thereby making it difficult to isolate the specific effects of probiotics. Third, considering the potential for colonization resistance to probiotics in the intestinal mucosa [4], the effects of probiotics were likely to be evident only during the administration period. Therefore, we conclude that long-term follow-up is not necessary in this study.

Finally, we discuss the effects of probiotics. The increase in the ratio of cluster En, which is characterized by pathogenic microorganisms, and the decrease in the obligate anaerobe counts, which are dominated by beneficial microbial organisms, indicated that dysbiosis, which was defined by Petersen and Round [5], progressed in the control group. However, as Dr Liqi [1] pointed out, there was no notable difference in the results other than dysbiosis between the 2 groups; therefore, our findings were not sufficient to conclude that probiotics are effective against CPB-induced intestinal damage.

We hypothesized that the limited effect of probiotics may be due to their inability to enhance the production of organic acids. Adequate production of organic acids can prevent intestinal epithelial damage and reduce systemic inflammation. Therefore, devising a probiotic administration method that promotes organic acid production might be a solution to achieve sufficient probiotic effects.

This study provides foundational knowledge regarding the interplay between CPB, intestinal injury, the gut microbiota, and probiotics in paediatric patients. Further research in this area will contribute to enhanced safety in paediatric cardiac surgery.

Conflict of interest: none declared.

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