Evaluating hydrogen ion mobilization during hemodialysis using only predialysis and postdialysis blood bicarbonate concentrations.

Introduction: The hydrogen ion (H⁺) mobilization model has been previously shown to provide a quantitative description of intradialytic changes in blood bicarbonate (HCO₃) concentration during hemodialysis (HD). The current study evaluated the accuracy of different methods for estimating the H⁺ mobilization parameter (H_m) from this model.

Methods: The study compared estimates of the H⁺ mobilization parameter using predialysis, hourly during the HD treatment, and postdialysis blood HCO₃ concentrations (H_m-full2) with those determined using only predialysis and postdialysis blood HCO₃ concentrations assuming steady state conditions (H_m-SS2) during the midweek treatment in 24 chronic HD patients treated thrice weekly.

Results: Estimated H_m-full2 values (0.163 ± 0.079 L/min [mean ± standard deviation]) were higher than, but not statistically different (p = 0.067) from, those of H_m-SS2 (0.152 ± 0.065 L/min); the values of H_m-full2 and H_m-SS2 were highly correlated with a correlation coefficient of 0.948 and a mean difference that was small (0.011 L/min). Further, the H⁺ mobilization parameter values calculated using only predialysis and postdialysis blood HCO₃ concentrations during the first and third HD treatments of the week were not different from those calculated during the midweek treatment.

Conclusions: The H⁺ mobilization model can be used to provide estimates of the H⁺ mobilization parameter without the need to measure hourly intradialytic blood HCO₃ concentrations.