[From sodium to dialysis quantification]. 
Sodium measurements are usually substituted by conductivity measurements in hemodialysis monitors.  Ionic dialysance can be calculated from conductivity measurements and used for quantification of dialysis dose (Kt).  Quantification of dialysis efficiency is based on the concept of clearance.  The clearance of a solute is the blood volume fully depurated per unit time.  The dialysance of a solute is the blood volume fully equilibrated with the dialysate entered into the dialyzer per unit time.  For a solute absent from the diatysate delivered to the dialyzer, dia[ysance is equal to clearance.  Because ions of quantitative importance (largely sodium) and urea have similar transfer characteristics through the dialyzer membrane, it can be expected that ionic dialysance is equal to urea dialysance and thus to urea clearance.  Actually several studies have shown that ionic dialysance is a very good estimation of urea clearance.  In comparison with the measurement of urea clearance, the measurement of ionic dialysance can be performed on-line, repeatedly and fully automatically, and is totally in expensive.