Harris DCH, Yuill E, Chesher DW
Correcting acidosis in hemodialysis: Effect on phosphate clearance and calcification risk

J Am Soc Nephrol (Dec) 6:1607-1612 1995

Dialytic removal of phosphorous is limited by its mobilization from a deep tissue pool into extracellular fluid during dialysis, therefore falling quite low intrdialytically and rebounding post-dialysis. A conflicting literature suggests that acetate-based dialysate or excessive alkalosis each may limit phosphate removal. Authors assessed dialytic phosphate removal, dialysis delivery, and indices of risk of metabolic calcification in 9 healthy, well dialyzed (Kt/V=1.4), patients undergoing standard hemodialysis (1.1-1.3 m2 cellulose acetate dialyzeers, QB=225-250 mL/min), in a randomized crossover comparison of three regimens: 1) dialysate bicarbonate adjusted to achieve pre-HD bicarbonate of 18-20 mM, 2) dialysate bicarbonate of 40 mM, plus po sodium bicarbonate as needed to achieve pre-HD bicarbonate of 24-26 mM, and 3) dialysate bicarbonate modeled from 28 to 40 mM during dialysis plus po supplementation as needed. There were no differences in phosphate clearance, mass transfer, serum concentrations of phosphorous, tribasic phosphate, or calcium at any time among the three treatments. Bicarbonate was lower, as was pH in the first (standard bicarbonate) treatment. More po bicarbonate supplementation was required in the modeled vs. high bicarbonate treatment. There was no adverse effects of bicarbonate supplementation, including no changes in interdialytic weight gain. The authors concluded that, as long as calcium and phosphorous were well controlled, there were no significant effects of standard, high and modeled dialysate bicarbonate on dialysis delivery, ultrafiltration, phosphate removal, hemodynamics or risk of metastatic calcification. Interpretation is limited by the excellent phosphate control in all subjects studied and the lack of in vivo validation of their index of calcification risk. Bicarbonate modeling does not appear justified based on claims of improved phosphate removal or acid-base control. (Umans)

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