A Pseudo‐One Compartment Model of Phosphorus Kinetics During Hemodialysis: Further Supporting Evidence

Abstract

A pseudo-one compartment model has been proposed to describe phosphorus kinetics during hemodialysis and the immediate post-dialysis period. This model assumes that phosphorus mobilization from tissues is proportional to the difference between the pre-dialysis serum concentration (a constant) and the instantaneous serum concentration. The current study is exploratory and evaluated the ability of a pseudo-one compartment model to describe the kinetics of phosphorus during two short hemodialysis treatments separated by a 60-min inter-treatment period without dialysis; the latter is the post-dialysis rebound period for the first short hemodialysis treatment. Serum was collected frequently during both hemodialysis treatments and the inter-treatment period to assess phosphorus kinetics in 21 chronic hemodialysis patients. Phosphorus mobilization clearance and pre-dialysis central distribution volume were previously estimated for each patient during the first hemodialysis treatment and the inter-treatment period. Assuming those kinetic parameters remained constant for each patient, serum phosphorus concentrations during the second treatment were used to estimate the driving force concentration (C ) for phosphorus mobilization from tissues during the second treatment. Treatment time (117 ± 14 [mean ± standard deviation] vs. 117 ± 14 min), dialyzer phosphorus clearance (151 ± 25 vs. 140 ± 32 mL/min), and net fluid removal (1.44 ± 0.74 vs. 1.47 ± 0.76 L) were similar during both short hemodialysis treatments. Measured phosphorus concentration at the start of the second hemodialysis treatment (3.3 ± 0.9 mg/dL) was lower (P < 0.001) than at the start of the first treatment or C (5.4 ± 1.9 mg/dL). Calculated C was 4.9 ± 2.0 mg/dL, not significantly different from C (P = 0.12). C and C were correlated (R = 0.72, P < 0.001). The results from this study demonstrate that the driving force concentration for phosphorus mobilization during hemodialysis is constant and not different from that pre-dialysis, providing further evidence supporting a fundamental assumption of the pseudo-one compartment model.

The impact of intradialytic cycling on the removal of protein-bound uraemic toxins: A randomised cross-over study

“…Rather surprisingly, also no increase in phosphate total solute removal was observed in the present study. From the complex kinetics of phosphate 22–24 it is clear that its removal is taking advantage of prolonged dialysis, as displacement from third compartments to the circulation is the rate limiting step for removal. 36 From the same reasoning it could be hypothesised that the mobilisation of phosphate from the deeper compartments is enhanced during intradialytic exercise.…”

“…21 However, urea is not representative for the kinetics of other small and water soluble toxins, such as phosphate. 22–24 For this molecule, intradialytic exercise appeared to be efficacious at improving its removal. 12,19,20,25 Especially for protein-bound uraemic toxins, kinetics are substantially dissimilar from those of urea.…”

A Bayesian approach for the identification of patient-specific parameters in a dialysis kinetic model

“…calcium, potassium and phosphorus, that play a crucial role for hydro-electrolyte equilibria. [16][17][18] To achieve more effective prediction models, multi-pool models have been introduced, allowing to describe the simultaneous contribution of different plasma solutes. 19 However, none of these models aim at characterizing the patientspecific solute kinetics in HD, apart from Ursino et al, 19 in which an individual estimation of few parameters characterizing solute kinetics has been performed.…”

Artificial Organs 2017: A Year in Review

“…Leypoldt et al of the Baxter Healthcare Corporation, Deerfield, IL USA investigated a pseudo‐one compartment model to describe phosphorus kinetics during HD and the immediate postdialysis period. The results demonstrated that the driving force concentration for phosphorus mobilization during HD is constant and not different from that predialysis, providing further evidence supporting a fundamental assumption of the pseudo‐one compartment model.…”