CORRECTING ACIDOSIS IN HEMODIALYSIS - EFFECT ON PHOSPHATE CLEARANCE AND CALCIFICATION RISK

Control of uremic acidosis by hemodialysis carries the potential risks of reducing phosphate clearance and worsening metastatic calcificatio n; modeling bicarbonate delivery has been proposed to adequately corre ct acidosis without impairing phosphate removal, To test the efficacy and safety of different methods for controlling acidosis, nine stable adults received in random order standard (S; dialysate HCO3- 30 to 34 mmol/L), high (H; 40 mmol/L) or modeled (M; 28 mmol/L, rising exponent ially to 35 mmol/L at 3 h, 40 mmol/L at 4 h) bicarbonate dialysis for 4 wk each, and were tested during the last two dialyses of each treatm ent, More oral bicarbonate capsules were required with M than H (2.8 /- 0.4 versus 1,4 +/- 0.4/day, P = 0,04) to maintain predialysis HCO3- at 24 to 26 mmol/L. Plasma HCO3- was significantly higher with H than M during dialysis, and than S before, during, and after dialysis, Pla sma inorganic phosphate, phosphate rebound, clearance of phosphate fro m plasma (80 to 90 mL/min) and mass transfer of phosphate into dialysa te (12 to 13 mmol/4 h dialysis) were no different among the three trea tments. Similarly, there were no differences in plasma concentration o f urea, total calcium, estimated ionized calcium, lipids, and potassiu m, clearance and mass transfer of urea, blood pressure, and symptoms w ith the three treatments. Estimated levels of tribasic inorganic phosp hate, the phosphate component of hydroxyapatite, were very similar bef ore and after each treatment, Plasma calcium x phosphate product was l ess than 3.5 mmol(2)/L(2) at all times with each treatment, A risk fac tor for metastatic calcification was calculated from the relative satu ration ratio of ifs principle component, hydroxyapatite (Ca-5 (PO4)(3) OH); this was no different among each of the treatments, and was not altered significantly by dialysis. Uremic acidosis can be fully correc ted by high or modeled bicarbonate dialysis without any reduction of p hosphate clearance or increased risk of metastatic calcification. The added cost of modeling technology is not justified by the criterion of phosphate clearance alone.