In our study, the REE/Wt did not change with kidney function change before and after transplantation, and it was higher than the age-matched BMR and close to the weight-matched cBMR in half of the patients both before and after transplantation. In patients who had previously undergone PEKT, some residual kidney function was observed, although they did not have a higher REE/Wt than those who had not undergone PEKT, suggesting that the effect of residual kidney function on the REE/Wt is not substantial. Nishimoto et al. [5] measured the REE/Wt in short children and compared the age-matched BMR and height-for-age-corrected BMR and reported that the REE/Wt was significantly higher than the age-matched BMR and not significantly different from the height-for-age-corrected BMR. Thus, even in pediatric patients with CKD, kidney dysfunction does not have a large effect on the REE/Wt, whereas physique is likely to have a large effect on the REE/Wt.
In this study, the RQ was examined simultaneously with the REE/Wt. The RQ after transplantation was significantly higher than that before transplantation. The resting RQ is approximately 0.80; the RQ is lower during starvation and increased lipid utilization and higher during excess carbohydrate intake and increased carbohydrate use due to exercise [6]. In our study, the mean RQ after transplantation was approximately 1, which was close to the typical RQ during exercise even though it was measured at rest.
In general, acid accumulation in the body during kidney failure is associated with increased CO2 production and a high RQ [7]. The venous blood CO2 concentration before and after transplantation in the patients in this study averaged 40.5 and 41.1 mmHg, respectively, a nonsignificant difference. Although reports on the RQ in patients with kidney failure are scarce, an older report indicates a relatively high RQ [8], whereas more recent reports indicate that such patients and those on long-term dialysis have a lower RQ than healthy individuals [9, 10]. However, those reports all concerned adult patients, and their situation may be different from that of children, who typically have an adequate caloric intake even when they have kidney failure, owing to their relatively smaller stature. Nakaya et al. [11] noted that the early morning fasting RQ of patients with kidney failure is lower than that of healthy individuals, suggesting that, as kidney failure progresses, the kidneys are unable to perform gluconeogenesis and may become starved owing to prolonged fasting. The cause of the increase in the RQ after kidney transplantation in this study is unknown, although gluconeogenesis of the transplanted kidney may increase glucose use. However, further accumulation of cases is necessary to examine other factors, such as the effect of caloric intake.
The main limitation of this study is that it comprises a small sample of Japanese pediatric patients. Thus, future studies should be conducted to determine whether the results differ according to ethnicity, and larger samples should be studied to improve statistical power.
In conclusion, measurements of the REE/Wt before and after transplantation in pediatric patients with CKD suggest that the REE/Wt is influenced by body size rather than kidney function. The RQ was significantly higher after kidney transplantation in this study, which may be due to increased carbohydrate use.