In vitro online postdilution hemodiafiltration: effect of various bicarbonate dialysis fluid concentrations on acid-base status

摘要

In hemodialysis, bicarbonate (HCO_3~1) balance c may be affected by the choice of HCO_3~1concentration in the dialysis fluid. In online postdilution hemodiafiltration (HDF), we studied the effect of three various HCO_3~1 dialysis fluid concentrations on HCO_3~1 transport across the hemodialyser membrane and on the final HCO_3~1 balance for the in vitro patient. Variation with time of HCO," patient concentration, and HCO_3~1 mass transfers (across the hemodialyser membrane and gained by the patient) were studied in six in vitro tests using c heparinized bovine blood. They were compared with theoretical HCO_3~1 concentrations calculated by a mathematical model using mass balance equation for the patient and a description of local mass transfer in the hemodialyser. In postdilution HDF, the HCO_3~1 mass transfer across the hemodialyser membranes becomes positive because HCO_3~1 is lost from blood to dialysis fluid by ultrafiltration. The gain of HCO," by the in vitro patient is only obtained with the amount of HCO_3~1 re-injected. Moreover it has been seen that depend- ing on the HCO," dialysis fluid concentration, HCO," plasma concentration kinetics are very different and that the HCO_3~1 dialysis fluid concentration determines the maximum plasma concentration. The representation of final HCO_3~1 plasma con- centration (Cpf) in function of the initial one (Cpi) can be seen as a tool to adapt the HCO_3~1 dialysis fluid concentration (Cdi). The data suggest the following empirical correlation for final HCO_3~1 plasma concentration: Cpf = 0.2Cpi + (Cdi - 6.4) Our single pool in vitro model seems to reproduce adequately the kinetics and mass transfer of HCO," with a small blood volume. It can be used to compare efficiencies of various HDF strategies (re-injection rate, HCO_3~1 dialysis fluid concentration).