Nitrogen balance studies and Kt/V urea in children undergoing chronic peritoneal dialysis.

Currently, urea kinetic modeling has been accepted for the routine evaluation of peritoneal dialysis (PD) through the calculation of Kt/V (normalized whole body urea clearance) and nPNA (normalized protein equivalent of total nitrogen appearance). In pediatric dialysis, the exact meaning of and target values for, those parameters is still under debate. We evaluated the mean values and correlations between Kt/V urea and parameters of nutrition. During a 12-month period, we prospectively performed 186 nitrogen balance studies in pediatric patients on chronic PD. We also assessed daily protein intake (DPI) by nutritional evaluation. Protein, albumin, urea, and creatinine were analyzed in dialysate and urine, collected once monthly. Dialysis adequacy was evaluated using monthly measurements of Kt/V urea and creatinine clearance (CCr) in urine and dialysate. All statistical comparisons were performed using the paired t-test. Two-way analysis of variance for repeated measures was used to calculate correlations. A p value less than 0.05 was considered significant. We studied 20 patients (15 boys, 5 girls) of mean age 5.1 +/- 4.7 years (range: 3 months - 14.8 years). Mean DPI in these patients was 3.52 +/- 1.1 g/kg/day. Weekly total Kt/V urea was 3.41 +/- 1.35, and residual Kt/V urea was 1.69 +/- 1.46. Weekly total and residual CCr were 72.4 +/- 70 L and 45 +/- 44 L respectively. Mean protein catabolic rate (PCR) was 0.84 +/- 0.33 g/ kg/day, showing a net nitrogen balance (NB = DPI - PCR) of +1.37 +/- 0.4 g/kg/day. The mean nPNA was 1.38 +/- 0.40 g/kg/day, with positive correlations with DPI, PCR, and total Kt/V (p < 0.001). Total Kt/V showed significant positive correlations with PCR (p < 0.001) and nPNA (p < 0.001), but not with NB (p = 0.23) and DPI (p = 0.21). A negative correlation was found between all urea kinetic parameters and plasma bicarbonate (p < 0.001). The values of Kt/V urea and nPNA in our patients were higher than those recommended in the adult literature. The positive correlations seen between Kt/V urea and nPCR and nPNA could not be demonstrated between Kt/V and DPI or NB, suggesting that the correlations could be the result of a mathematical association. The negative correlations between plasma bicarbonate and urea kinetic variables suggest a negative impact of acidosis on nutrition status in our patients.

Adequacy and nutrition in pediatric peritoneal dialysis.

Outcomes for pediatric peritoneal dialysis (PD) patients are closely related to dialysis adequacy and nutrition, which need to be measured frequently using a number of laboratory parameters. Although the critical meaning of adequacy and nutrition in the long-term prognosis of dialyzed children is well-documented, PD prescriptions are still largely empirical. Our objective was to evaluate nutritional and dialytic parameters in PD children (urea, creatinine, and albumin excretion in dialysate and urine, and daily protein intake); to measure peritoneal equilibration test (PET) results, Kt/V, normalized equivalent of protein nitrogen appearance (nPNA) and nitrogen balance; and to study the correlations between those variables. We performed 59 prospective laboratory measurements in 15 stable PD patients (7 boys; mean age: 6.7 years; age range: 1.1-14.8 years) during 6 months of follow-up. Creatinine, urea, total protein, and albumin were measured in plasma, urine, and dialysate. We calculated PET, Kt/V, daily dietary protein intake (DPI), protein catabolic rate (PCR), and nPNA. All statistical comparisons used the paired t-test, and correlations were calculated by two-way analysis of variance for repeated measures. A value of p < 0.05 was considered significant. The mean 4-hour dialysate-to-plasma ratio (D/P) of creatinine was 0.78 +/- 0.02 at month 0 and 0.74 +/- 0.13 at month 6 [p = nonsignificant (NS)]. The mean final-dialysate-to-initial-dialysate ratio (D/D0) of glucose was 0.35 +/- 0.11 and 0.34 +/- 0.08 at the same intervals (p = NS). The D/P creatinine showed an inverse correlation with patient age and body surface area, and the D/D0 glucose ratio showed a positive correlation with both of those parameters (p < 0.05). Weekly total and residual Kt/V urea were 3.41 +/- 0.86 and 1.49 +/- 1 respectively. The daily DPI was 3.32 +/- 1.05 g/kg, and the daily PCR was 1.32 +/- 0.47 g/kg, showing a positive net protein balance (DPI-PCR = +2 g/kg daily), which was negatively correlated with age and body surface area (p < 0.001). The mean daily nPNA was 0.94 +/- 0.33 g/kg, which was negatively correlated with age and body surface area (p < 0.05, r = -0.51), and positively correlated with daily DPI and total and residual Kt/V (p < 0.0001). Our patients could be classified as high-average transporters, with low-average ultrafiltration. The high transport state was associated with greater peritoneal albumin losses, a point of concern at younger ages. Total Kt/V and nPNA were higher for the youngest patients, suggesting a favorable nutrition status, but more studies are needed to determine the best value for both parameters in clinical practice.