High- and low-flux acetate-free biofiltration: experimental assessment of calcium mass balance and intact parathyroid hormone behaviour

We studied total calcium mass balance and plasma intact parathyroidhormone behaviour in 10 uraemic patients who underwent acetate-freebiofiltration carried out in accordance with six different dialyticschedules, where either a polyacrylonitrile or a polysuiphonemembrane was used. Schedules 1 and 2 involved a reinfusion flowrate of 33.3 ml/mm with a dialysate calcium concentration (DCa)of 1.75 and 2 mmol/l respectively; in schedule 3, 4, 5 and 6reinfusion flow rate amounted to 50 ml/mm and DCa was respectivelyof 1.75, 2, 2.25 and 2.5 mmol/l. Dehydration remained unchangedin all schedules: 700 g/h. Finally high- and low-flux acetate-freebiofiltration are able to induce different Ca mass balance whichmay suit different therapeutic contexts. Ca mass balance waseither positive or negative depending on reinfusion flow rateand DCa. With a reinfusion flow rate of 33.3 ml/mm a DCa ofat least 2 mmol/l was necessary to obtain a positive mass balance,while with a reinfusion flow rate of 50 ml/mm DCa had to equal2.25 mmol/l. In high-flux acetate- free biofiltration, the estimationof predialytic Ca²⁺ and DCa values, using a simple formula,allows prediction of the mass balance that will be attained.At the end of acetate-free biofiltration, intact parathyroidhormone always decreased when a polyacrylonitrile membrane wasemployed while it increased, in the presence of negative Camass balance with a polysulphone membrane.