Kt/V and nPNA in pediatric peritoneal dialysis: a clinical or a mathematical association?

The relationship between dialysis dose and nutrition is a field of particular interest in chronic pediatric dialysis (PD), and a positive correlation between ureaKt/V and nPNA has been published, suggesting a better nutritional status is associated with higher dialysis doses. However, this relationship has also been criticized as being the result of a mathematical coupling resulting from the same variables. The objective of the study was to establish the relationship between dialysis dose (Kt/V) and nutritional variables: daily protein intake (DPI), protein catabolic rate (PCR), protein equivalent of total nitrogen appearance (PNA) and nitrogen balance (NB) in dialyzed children. A cohort, prospective, observational study was carried out, for which 223 biochemical measurements were performed in 20 patients, ages 1 month to 14.3 years old (13 males), under PD for a 12-month period of follow-up. Monthly residual and total ureaKt/V, DPI, PCR, nPNA and NB were calculated, and the correlation between Kt/V and the nutritional parameters was evaluated. The Borah equation was used to calculate the nPNA. The data are reported as the mean plus or minus the standard error. All statistical comparisons were done with a paired t test, and two-way ANOVA for repeated measures was used to calculate correlations. A P < 0.05 was considered significant. Mean total and residual Kt/V was 3.4 +/- 1.3 and 1.69 +/- 1.27, respectively; nPNA and PCR were 1.38 +/- 0.44 and 1.39 +/- 0.43 g/kg/day, daily protein intake (DPI) was 3.25 +/- 1.27 g/kg/day, and NB showed a value of 1.86 +/- 1.25 g/kg/day. A significant positive correlation was found between Kt/V and DPI, PCR, DPC and nPNA (all values P < 0.0001), but no correlation was found between total and residual Kt/V vs. nitrogen balance (P:ns). Total Kt/V showed a significant positive correlation with nPNA, but it did not show any correlation with nitrogen balance, suggesting that the relationship with nPNA is the result of a mathematical association calculated from the same variables.