Reliability of delivered dialysate sodium concentration

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.

Fallacies and Pitfalls of Dialysis Sodium Prescription and Control

“…shows higher dialysate sodium in Gambro machines compared to Fresenius machines (with the same set value). Similar results were recently reported by Ekbal et al [14], who found higher dialysate sodium in the Dialog dialysis machine of B. Braun compared to 4008 type of Fresenius. Approximately 3-4 mmol/L higher dialysate sodium in Gambro machines compared to 5008 Fresenius and DBB05 of Nikkiso were also seen by Descombes et al [3].…”

Acute hemodialysis in a young man with severe symptomatic hyponatremia and kidney injury

“…There may also be a discrepancy between prescribed dialysate sodium concentration and that delivered. The reported discrepancies are ±2 mmol/L up to +7 mmol/L, with higher prescribed dialysate sodium concentrations associated with greater differences . Finally, the Gibbs‐Donnan effect also impacts sodium diffusion across the dialyzer membrane .…”

“…The reported discrepancies are 62 mmol/ L up to 17 mmol/L, with higher prescribed dialysate sodium concentrations associated with greater differences. 7,8 Finally, the Gibbs-Donnan effect also impacts sodium diffusion across the dialyzer membrane. 6 This effect results from the formation of an electro-chemical boundary on the blood side of the dialyzer composed of negatively charged proteins and accompanying cations.…”

Changes in Total Protein Concentration Due to Fluid Removal During and Shortly after Hemodialysis

“…The exact point where dialysate sodium would result in a net zero diffusive transport of sodium during dialysis is affected by Donnan equilibrium, as well as the relation of plasma water sodium to plasma sodium level. Also, dialysis solution sodium used in these analyses was the nominal level, and the nominal level has been shown to be different from the measured value [21]. However, the HEMO Study dataset included patients in whom either large positive or large negative sodium gradients were present and there was no detectable impact of a sodium gradient on the magnitude of the increase in serum total protein concentration during dialysis relative to the calculated change in total body water.…”