Validity of the hydrogen ion mobilisation model during haemodialysis with time-dependent dialysate bicarbonate concentrations

Abstract

Background:

The hydrogen ion (H⁺) mobilisation model has been previously shown to accurately describe blood bicarbonate (HCO₃) kinetics during haemodialysis (HD) when the dialysate bicarbonate concentration ([HCO₃]) is constant throughout the treatment. This study evaluated the ability of the H⁺ mobilization model to describe blood HCO₃ kinetics during HD treatments with a time-dependent dialysate [HCO₃].

Methods:

Data from a recent clinical study where blood [HCO₃] was measured at the beginning of and every hour during 4-h treatments in 20 chronic, thrice-weekly HD patients with a constant (Treatment A), decreasing (Treatment B) and increasing (Treatment C) dialysate [HCO₃] were evaluated. The H⁺ mobilization model was used to determine the model parameter (H_m) that provided the best fit of the model to the clinical data using nonlinear regression. A total of 114 HD treatments provided individual estimates of H_m.

Results:

Mean ± standard deviation estimates of H_m during Treatments A, B and C were 0.153 ± 0.069, 0.180 ± 0.109 and 0.205 ± 0.141 L/min (medians [interquartile ranges] were 0.145 [0.118,0.191], 0.159 [0.112,0.209], 0.169 [0.115,0.236] L/min), respectively; these estimates were not different from each other (p = 0.26). The sum of squared differences between the measured blood [HCO₃] and that predicted by the model were not different during Treatments A, B and C (p = 0.50), suggesting a similar degree of model fit to the data.

Conclusions:

This study supports the validity of the H⁺ mobilization model to describe intradialysis blood HCO₃ kinetics during HD with a constant H_m value when using a time-dependent dialysate [HCO₃].