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

Abstract

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.

Peritoneal Dialysis in Children

“…The relationship between Kt/V urea and the normalized protein equivalent of nitrogen appearance (nPNA) has often been criticized as merely being the result of mathematical coupling [44]. Finally, a higher Kt/V was associated with a lower serum albumin level in children, suggesting that enhancing PD dose, i.e., to a Kt/V urea of more than 2.75, may provide no further benefit, owing to an increased loss of albumin into the dialysate [37].…”

Nutrition aspects in children receiving maintenance hemodialysis: impact on outcome

“…\kern-\nulldelimiterspace} {{\text{Vd + 0}}{\text{.17}}}}$$\end{document}where Vd represents total body water after dialysis (0.58 × weight in kilograms). We recommend that nPCR be measured monthly, together with Kt/V in dialysis units where Kt/V is assessed.Cano et al [27], in an observational study, found significant positive correlation between Kt/V vs daily protein intake (DPI), protein catabolic rate (calculated from measuring nitrogen losses in urine and dialysate) and normalized protein nitrogen appearance (which they derived from urea generation rate) but failed to observe correlation between Kt/V and nitrogen balance in 20 children undergoing long-term peritoneal dialysis. The absence of a relationship between dialysis dose and nitrogen balance suggested that the correlation observed between dialysis dose and protein catabolic rate resulted from a mathematical tautology; however, DPI in their patient population correlated with PCR (r = 0.9), suggesting that PCR was, in fact, reflective of nutritional status.…”

Advances in renal replacement therapy as a bridge to renal transplantation

“…Cano et al. found that PNA demonstrated a strong positive correlation with Kt / V in 20 patients, but did not correlate with nitrogen balance (58). They concluded that PNA was more of a mathematical artifact than a true clinical indicator of nutrition status.…”

“…Edifonti et al studied 43 pediatric patients and found that nearly 50% of patients malnourished, based on an anthropometic-BIA nutrition score that placed them at less than the third percentile (57). Cano et al found that PNA demonstrated a strong positive correlation with Kt/V in 20 patients, but did not correlate with nitrogen balance (58). They concluded that PNA was more of a mathematical artifact than a true clinical indicator of nutrition status.…”