Evaluation of a Pseudo-One-Compartment Model for Phosphorus Kinetics by Later-Phase Dialysate Collection during Blood Purification

Abstract

Purpose

Phosphorus removal is a major issue to assess for physicians engaging in hemodialysis. A pseudo-one-compartment model was reported as a novel model for phosphorus kinetics. We aimed to evaluate the adequacy of this model from the standpoint of the total mass of removed phosphorus during prolonged treatment.

Methods

Dialysate was collected during 6-h hemodialysis and hemodiafiltration treatment in 5 patients. Later-phase (from 4 to 6 h) dialysate was collected separately. Mobilization clearance (K_m and dialyzer clearance (K) were calculated by simple arithmetic operations utilizing stable serum phosphorus concentrations in this later phase. Volume of the accessible compartment (V₀) was estimated by a fitting method. Amounts of removed phosphorus were calculated with these parameters and compared with measured values. The best sampling time points during treatment were also assessed, when the parameters were determined by serial serum phosphorus concentrations alone.

Results

Pearson's correlation coefficient (R) between calculated and measured values of removed phosphorus was 0.991 and the concordance correlation coefficient (ρ) was 0.987. When K_m, K and V₀ were determined by serial serum concentrations alone, including those at 0, 1, 4, and 6 h, the calculated mass of removed phosphorus had high R (0.974–0.975) or ρ (0.966–0.972) with the measured values.

Conclusions

We confirmed that a pseudo-one-compartment model is useful for the estimation of removed phosphorus mass during prolonged blood purification by collecting dialysate. When the parameters are determined by a fitting method using serial serum concentrations alone, sampling at 0, 1, 4, and 6 h seems to be adequate.