HIGH-FLUX AND LOW-FLUX ACETATE-FREE BIOFILTRATION - EXPERIMENTAL ASSESSMENT OF CALCIUM MASS-BALANCE AND INTACT PARATHYROID-HORMONE BEHAVIOR

We studied total calcium mass balance and plasma intact parathyroid ho rmone behaviour in 10 uraemic patients who underwent acetate-free biof iltration carried out in accordance with six different dialytic schedu les, where either a polyacrylonitrile or a polysulphone membrane was u sed. Schedules 1 and 2 involved a reinfusion flow rate of 33.3 ml/min with a dialysate calcium concentration (DCa) of 1.75 and 2 mmol/l resp ectively; in schedule 3, 4, 5 and 6 reinfusion flow rate amounted to 5 0 ml/min and DCa was respectively of 1.75, 2, 2.25 and 2.5 mmol/l. Deh ydration remained unchanged in all schedules: 700 g/h. Finally high- a nd low-flux acetate-free biofiltration are able to induce different Ca mass balance which may suit different therapeutic contexts. Ca mass b alance was either positive or negative depending on reinfusion flow ra te and DCa. With a reinfusion flow rate of 33.3 ml/min a DCa of at lea st 2 mmol/l was necessary to obtain a positive mass balance, while wit h a reinfusion flow rate of 50 ml/min DCa had to equal 2.25 mmol/l. In high-flux acetate-free biofiltration, the estimation of predialytic C a2+ and DCa values, using a simple formula, allows prediction of the m ass balance that will be attained. At the end of acetate-free biofiltr ation, intact parathyroid hormone always decreased when a polyacryloni trile membrane was employed while it increased, in the presence of neg ative Ca mass balance with a polysulphone membrane.