One of the most important pathogenetic factors involved in the onset of intradialysis arrhytmias is the alteration in electrolyte concentration, particularly potassium (K+). Aim of the present study was to evaluate K+ kinetics during bicarbonate hemodialysis (HD).
K+ kinetics was studied in 63 stable prevalent anuric patients, undergoing one 4-hour midweek bicarbonate HD session. Dialysate K+ concentration was 2.0 mmol/L. Blood samples were obtained from the inlet blood tubing immediately before the onset of dialysis and at t60, t120, t180 min and at end of the sessions for the measurement of plasma K+, bicarbonates and pH. Direct dialysate quantification was utilized for K+ mass balances (K+MB). Direct potentiometry with an ion-selective electrode was used for K+ measurements.
Mean pre- and postdialysis plasma K+ concentrations were 5.3 + 0.6 and 3.7 + 0.4 mmol/L (P < 0.0001). Mean K+MBs were - 86.7 + 22.6 mmol. Blood pH and bicarbonates had a statistically significant increase (P < 0.0001). Several bivariate linear regression analyses were performed, having K+MB as dependent variable. The bivariate regression analyses, which resulted statistically significant, had the following independent variables: mean intradialysis plasma K+ (R2 0.588, P < 0.0001), area under the curve (AUC) of hourly inlet dialyzer diffusion concentration gradients between plasma and dialysate (mmol/L*min) (R2 0.545, P < 0.0001), gender, blood bicarbonates, ultrafiltration volume, pre-and post-HD body weight. Among the independent variables, only mean intradialysis plasma K+ (P < 0.0001) and AUC of hourly inlet dialyzer diffusion concentration gradients (P < 0.036) predicted K+MB at the multiple regression analysis (Figure 1).
The strenght of this study resides in the accuracy of the measurements of K+MBs by means of direct dialysate quantification. K+MBs have K+ plasma → K+ dialysate gradient as the main determinant . A much less important role plays the development of intradialysis metabolic alkalosis.
