Behaviour of phosphate removal with different dialysis schedules

Abstract

and (iii) a detrimental eVect on renal function [10], that can still be maintained at a significant level in patients (uPi mmol/day=’1.11+1.39◊GFR; r=0.91, continuous ambulatory peritoneal dialysis (CAPD) P<0.001), stressing the importance of the preservation patients. of residual renal function in maintaining a good Before addressing the problem of Pi removal by metabolic balance in CAPD. dialysis treatment, it might be useful to recall some When we considered the factors aVecting the dialytic points on Pi body distribution. Of the more than 650 g removal of phosphate in our CAPD patients by means of Pi contained in a medium-sized man, ~85% is of a multiple regression analysis ( Table 1), we found contained in bone, 14% in the cells and only 1% or that plasma Pi concentration plays the main role. less is in the plasma. It is also important to bear in Another important factor is represented by the glucose mind that the bulk of intracellular Pi is represented by concentration in the dialysate, and its influence on organic phosphate (nucleoside phosphate compounds, Pi removal was independent of ultrafiltration rate. phosphorylated enzymes, 2,3-diphosphoglycerate, pho- Finally, Pi removal by peritoneal dialysis was greatly sphocreatine, etc.) at 10‐100 times the concentration aVected by dialysate volume, with a calculated removal of inorganic phosphate with which it is in equilibrium. of ~95 mmol/week at a dialysate volume of 12 l per The inorganic intracellular phosphate is in turn in equilibrium with the extracellular Pi, with an intracellu- Table 1. Stepwise multiple regression analysis of daily Pi dialysis lar/extracellular ratio of ~0.6 [11]. As a consequence, removal (mmol/day), taken as dependent variable, in 35 CAPD any variation in plasma Pi concentration can aVect patients in relation to the following predictor independent variables: both intracellular inorganic and organic phosphate serum Pi concentration (mmol/l ), glucose dialysate inlet concentracontent. tion (%), dialysate inlet volume ( l/day)