Comparison of pressure-controlled vs.volume-controlled mode in postdilutional on-line haemodiafiltration
Abstract
The main benefit of convective therapies is high clearance for middle and large molecular weight substances. Efficacy of their removal in post-dilutional HDF is given by the filtration rate (QF) and the absolute "convective dose" by the total filtered volume (Vconv).
From purely physical point of view, Vconv should be as high as possible. At present, there are in principle two control modes - manual and automatic.
In manual mode, the operator sets the Vconv and session time (T) and the whole session runs with constant QF (QF= Vconv /T). In automated control mode (e.g.
AutoSub(R) in Fresenius machines or UltraControl(R) in Gambro machines), Vconv is controlled by an automatic algorithm via transmembrane pressure (TMP) which continuously tries to maximize the QF during the whole HDF session. The Vconv value to be reached is thus not known in advance.