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 (HCO 3 ) 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 HCO 3 concentrations (H m -full2) with those determined using only predialysis and postdialysis blood HCO 3 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 HCO 3 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 HCO 3 concentrations.