Dialysate conductivity is routinely used as a surrogate for dialysate sodium concentration. However, dialysis machine manufacturers apply different conductivity temperature correction coefficients. With the same conductivity in dialysis machines manufactured by different manufacturers, dialysate sodium may significantly differ. Also, electrolyte prescriptions are individualized (K, Ca, HCO³) and this is associated with another variation in dialysate sodium in the order of 1–5 mmol/L and both deviations are cumulative and chronic for each patient. Equivalence of the prescribed dialysate sodium and the concentration measured in it is not granted. Both variables differ and it is machine dependent! This paper analyses those variations from a technical point of view and suggests how to detect them and how to deal with or avoid them in clinical practice.

Phosphorus removal by hemoelimination procedure is a important mechanism to maintain phosphorus level in acceptable level in patients on dialysis. Phosphorus is removed by both diffusion and convection, but in clinical practice, it is not possible to differentiate the contribution of this two transport modalities. We used Gutzwiller formula to quantify the amount of removed phosphorus and compared it in low-flux hemodialysis (LFHD), high-flux hemodialysis (HFHD), and on-line hemodiafiltration (HDF). There were no significant differences in phosphorus predialysis concentration, duration of procedure, processed blood volume and ultrafiltration, e.g., factors, which could possibly influence phosphorus elimination. All three tested dialysis modes also did not differ in urea dialysis dose (Kt/V) as a parameter of small molecular weight removal (LFHD, 1.50 ± 0.04 vs HFHD, 1.5 ± 0.06 vs HDF, 1.5 ± 0.05). The amount of removed phosphorus in LFHD, HFHD, and HDF was 34.0 ± 1.2, 37.8 ± 1.6, and 38.3 ± 1.4 mmol, respectively. Statistically significant increase in phosphorus removal was seen only with use of high-flux membrane (HFHD and HDF) when compared with the low-flux one. No difference was, however, found between HFHD and HDF. It can thus be concluded that phosphorus removal in all three dialysis modes is a predominantly diffusive issue and contribution of convection to it is minor to negligible.