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Abstract: TH-PO355

Bias Between In Vitro and In Vivo Mass-Transfer Coefficient of Urea (KoA) Is Larger in Pediatric Than in Adult Patients on Chronic Hemodialysis

Session Information

Category: Dialysis

  • 701 Dialysis: Hemodialysis and Frequent Dialysis


  • Gotta, Verena, University of Basel Children''s Hospital, Basel, Switzerland
  • Marsenic Couloures, Olivera, Yale University , New Haven, Connecticut, United States
  • Pfister, Marc, University of Basel Children's Hospital, Basel, Switzerland, Hilterfingen, Switzerland

Hemodialysis (HD) prescription with respect to blood flow (QB) dialysate flow (QD) and filter KoA significantly differs between pediatric and adult patients. This may explain why urea dialytic clearance (KD) has been observed to be significantly underpredicted from QB, QD and KoA in pediatric HD patients using a mechanistic equation. The objective of this analysis was to evaluate factors that could explain this bias, assuming that it results from a bias between reported in vitro determined KoA and actual in vivo KoA.


An urea kinetic model previously developed in adult patients was scaled to 923 paediatric and young adult patients aged 1-29 years based on a priori physiologic knowledge (inter-compartmental clearance and volumes of distribution; “base model”). Utilizing data from 2676 HD sessions of those patients with pre- and post-HD urea concentration measurements, a mixed effect modelling approach was applied to evaluate the relationship between individual estimates of KoA correction factors (fKoA) required for unbiased prediction of KD (as indicated by unbiased post-HD urea predictions), and prescription related parameters (QB, QD, QD/QB ratio, filter reuse, low/high-flux, ultra-filtration rate, duration of treatment).


QD/QB ratio was the parameter most strongly associated with individual estimates of fKoA (≈ -10%, 10%, 100% and 200% increased in vivo KoA estimated at QD/QB ratios of 1.5, 2, 5, and 10, respectively; p<0.001), explaining 18% of inter-individual variability (decrease from 42.8 to 35.1%). Inclusion of QD/QB ratio as a covariate removed bias observed with QB and QD. A proposed correction equation for QB (true QB lower than nominal QB at rates >200 mL/min) also corrected bias observed at QB > 300 mL/min, but did not reduce inter-individual variability. Inclusion of session duration, low-flux filters, and ultra-filtration rate did further improve the model fit, however with small reductions in inter-individual variability.


While in vivo KoA has been reported to be lower in adult patients than established in vitro, the opposite was observed for pediatric patients in the present study. The observed bias could best be explained by high QD/QB ratios used in pediatric patients indicating that dialyzers require specific characterization under pediatric conditions.


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