Prediction of Equilibrated Urea in Children on Chronic Hemodialysis

Abstract

Urea rebound (UR) after hemodialysis (HD) requires the use of equilibrated urea (Ceq) instead of immediate end-dialysis urea (Ct) for correct quantification of HD, which is impractical. A new formula for predicting Ceq in children is suggested in our study. Thirty eight standard pediatric HD sessions (single pool Kt/V = 1.70 +/- 0.35, K = 4.65 +/- 1.14 ml/min/kg, UF coeff. = 3.2-6.2 ml/h/mm Hg, t = 3.80 +/- 0.46 h) in 15 children (M: 6, F: 9), ages 14.5 +/- 3.28 years were analyzed. Blood samples were taken: before, 70 min from the start, at the end, and 60 min after the end of HD sessions. After correlating UR (20.32 +/- 7.74%) to various HD parameters, we found that it was mainly determined by HD efficiency parameters. Therefore we correlated Ceq to HD efficiency parameters (Ct, urea reduction ratio, Kt/V, and K/V) and found a very high correlation between Ct and Ceq (r = 0.973). Linear regression analysis was used to further investigate this relationship, and a new formula to predict Ceq from Ct was obtained (Ceq = 1.085 Ct + 0.729, R2 = 0.946, SE = 0.49, absolute residuals = 0.38 +/- 0.29 mmol/L). In a validation study (10 HD sessions with new set of urea blood samples) the results obtained by the new formula were compared with measured values of Ceq and those obtained by the Smye formulae. Values predicted by the new formula (9.91 +/- 2.92 mmol/L) were not significantly different from the measured values (10.33 +/- 3.44 mmol/L). Absolute error of the new formula was 0.78 +/- 0.73 mmol/L, median 0.65; ie., 6.93 +/- 5.3%, median 7.7%. Ceq predicted by the Smye formulae (10.95 +/- 4.18 mmol/L) also did not significantly differ from the measured values, but absolute error of predicted values was markedly higher (1.21 +/- 0.90 mmol/L, median 0.89; 11.73 +/- 7.72%, median 10.11%; p < 0.05). When predicted Ceq was used for calculating equilibrated Kt/V (eKt/V), the new formula resulted in lower absolute error (0.09 +/- 0.07, median 0.08) than the Smye method (0.14 +/- 0.08, median 0.12). We conclude that our simple formula is sufficiently accurate in predicting Ceq in standard pediatric HD and that it is more accurate than the existing Smye formulae, while requiring only pre- and post-HD urea samples. We suggest the use of the new formula for predicting Ceq, which can then be used instead of Ct for a more accurate estimation of double pool Kt/V, URR, V, and PCR.

Hemodialysis in children: general practical guidelines

“…The measures most widely used to gauge dialyzer treatment are Kt / V , that is dialyzer urea clearance ( K ) multiplied by duration ( t ) of the dialysis session and divided by urea volume ( V ) of distribution, and the normalized protein catabolic rate (nPCR) [57, 58, 59]. Urea dialytic reduction rate (URR) is derived from the pre and post-dialysis serum urea values and quantitates urea removal by dialysis.…”

“…URR is also correlated with the amount of urea dialytic removal ( Kt ) compared to the amount of urea body content ( V ) and thus to Kt / V . Usually urea dialytic clearance in children is low in comparison with the high Kie which is between 200 to 1000 mL min −1 (6 to 12 mL min −1  kg −1 BW) [58, 61]. Nevertheless, after dialysis the concentration of urea in plasma increases rapidly in an initial period, usually until 60 min postdialysis [62].…”

Mathematical Analysis of Urea Rebound in Long‐term Hemodialysis Patients

“…While there is an advantage in that these methods avoid taking a blood sample after HD and do not detain the patient beyond the treatment time, the accuracy of these methods is influenced by the method and timing of taking the intradialytic blood sample (13,14). If severe vascular access recirculation is present, and if the blood sample is taken at full blood flow without slowing or stopping it to prevent sample dilution with recirculated blood, the intradialytic BUN will be artificially low and will result in significant overestimation of the true eqBUN, and as a consequence a significant underestimation of the true Kt/ V ‐value (15). Thus, it is necessary to pay careful attention to the method of intradialytic blood sample when they were performed.…”

Application of Individualized Bayesian Urea Kinetic Modeling to Pediatric Hemodialysis

“…2,8,9 To take into account the post-HD urea rebound (UR) 10 -12 and quantify the delivered HD dose, such a method requires a blood sample 1 hour after HD to obtain the true equilibrated blood urea nitrogen (BUN) and Kt/V. [13][14][15][16][17] This additional sampling 1 hour after the completion of dialysis can be difficult to obtain in the pediatric setting, making the determination of delivered HD difficult to calculate. There is therefore a need for a simple and accurate determination of HD dose and treatment adjustments in the pediatric population, because size, dynamics of substance handling, and volume of distribution of substances to be cleared in children vary greatly from infancy through adolescence, and ultimately adulthood.…”

“…Results of this work were previously published. 12,15,17 For use in the current study, this dataset was de-identified and therefore exempt from Institutional Review Board (IRB) approval.…”