Models to assess nitrogen losses in pediatric patients on chronic peritoneal dialysis

To develop models to estimate nitrogen (N) losses of children on chronic pe ritoneal dialysis (CPD) from easily measurable indexes and laboratory tests , we measured the N content and all nitrogenous compounds in dialysate (D), urine (U), and feces over 3 days in 19 pediatric patients on CPD. Total me asured N losses (TNm) were 5.56+/-2.26 g/day (69.9+/-11.1% in dialysate, 16 .3+/-10.6% in urine, and 13.6+/-4.6% in feces). Correlation coefficients be tween measured dialysate and urinary N losses and the single nitrogenous co mpounds indicated values of over 0.9 only for urea in dialysate and urine; fecal N losses correlated well with body surface area (BSA). Taking into ac count these correlations, we developed a univariate additive model and thre e multivariate models to predict total estimated N losses (TNe). The best p rediction of TNm was obtained with model 3, which considered not only urea output in dialysate and urine but also dialysate protein loss and BSA: TNe (g/day)=0.03+1.138 UN urea+0.99 DN urea+1.18 BSA+0.965 DN protein. A confir matory analysis performed on a second group of 23 pediatric patients on CPD , using all four models, showed a higher percent age of studies with a rela tive difference between TNm and TNe less than 10% for model 3 than for the other models. Thus, N losses of pediatric patients on CPD can be estimated from measured urea and protein losses in dialysate and urea loss in urine, together with BSA.