Ranking of factors determining potassium mass balance in bicarbonate haemodialysis

One of the most important pathogenetic factors involved in the onset of intradialysis arrhytmias is the alteration in electrolyte concentration, particularly potassium (K+). Two studies were performed: Study A was designed to investigate above all the isolated effect of the factor time t on intradialysis K+ mass balance (K+MB): 11 stable prevalent Caucasian anuric patients underwent one standard (similar to 4 h) and one long-hour (similar to 8 h) bicarbonate haemodialysis (HD) session. The latter were pair-matched as far as the dialysate and blood volume processed (90 L) and volume of ultrafiltration are concerned. Study B was designed to identify and rank the other factors determining intradialysis K+MB: 63 stable prevalent Caucasian anuric patients underwent one 4-h standard bicarbonate HD session. Dialysate K+ concentration was 2.0 mmol/L in both studies. Blood samples were obtained from the inlet blood tubing immediately before the onset of dialysis and at t(60), t(120), t(180) min and at end of the 4- and 8-h sessions for the measurement of plasma K+, blood bicarbonates and blood pH. Additional blood samples were obtained at t(360) min for the 8 h sessions. Direct dialysate quantification was utilized for K(+)MBs. Direct potentiometry with an ion-selective electrode was used for K+ measurements. Study A: mean K(+)MBs were significantly higher in the 8-h sessions (4 h: -88.4 +/- 23.2 SD mmol versus 8 h: -101.9 +/- 32.2 mmol; P = 0.02). Bivariate linear regression analyses showed that only mean plasma K+, area under the curve (AUC) of the hourly inlet dialyser diffusion concentration gradient of K+ (hcgAUCK(+)) and AUC of blood bicarbonates and mean blood bicarbonates were significantly related to K+MB in both 4- and 8-h sessions. A multiple linear regression output with K+MB as dependent variable showed that only mean plasma K+, hcgAUCK(+) and duration of HD sessions per se remained statistically significant. Study B: mean K(+)MBs were -86.7 +/- 22.6 mmol. Bivariate linear regression analyses showed that only mean plasma K+, hcgAUCK(+) and mean blood bicarbonates were significantly related to K+MB. Again, only mean plasma K+ and hcgAUCK(+) predicted K+MB at the multiple linear regression analysis. Our studies enabled to establish the ranking of factors determining intradialysis K+MB: plasma K+ -> dialysate K+ gradient is the main determinant; acid-base balance plays a much less important role. The duration of HD session per se is an independent determinant of K+MB.