Reliability of delivered dialysate sodium concentration

Hemodial Int. 2016 Oct;20 Suppl 1:S2-S6. doi: 10.1111/hdi.12465.

Abstract

Background The results of studies investigating the effects of hyponatraemic dialysates have been mixed, with some reporting positive effects including reduction in blood pressure and inter-dialytic weight gains, whereas others have not been able to demonstrate any effect. These studies assume that setting a lower dialysate sodium results in the delivery of a hyponatraemic dialysate. We therefore measured delivered sodium to determine reliability. Methods We measured dialysate sodium in 10 BBraun Dialog+® and 6 Fresenius 4008H dialysis machines, which had been set up to deliver a sodium of 136 mmol/L, using flame photometry and indirect ion selective electrode (ISE) methods. Results Dialysate conductivity was 13.85 ± 0.05 mS/cm, but dialysate sodium measured by flame photometry was 141.8 ± 2.9 mmol/L, and 142.5 ± 2.4 mmol/L by ISE. Both dialysis machines delivered a dialysate sodium in excess of the 136 mmol/L set, with a mean bias of 7.0 ±2.1 mmol/L for the Dialog+® , and 3.7 ± 2.6 for the 4008 with the flame photometer method, and a mean bias of 6.3 ± 1.3 mmol/L for the Dialog+® , and 6.8 ± 3.7 for the 4008 by ISE. Conclusion It is assumed when setting a dialysate sodium concentration that this sodium concentration is delivered. However we found that the dialysate sodium concentration delivered was greater than that set, despite the dialysis machines reporting a conductivity measurement in keeping with a lower sodium dialysate. Trials of lowered dialysate sodium therefore need to measure dialysate sodium concentrations to ensure what has been set is delivered.

Keywords: Dialysis; acute kidney injury; complications; renal replacement therapy.