Measuring Plasma Conductivity to Detect Sodium Load in Hemodialysis Patients

Background: Sodium thiosulfate therapy has been proposed for calcific uremic arteriolopathy and nephrogenic systemic fibrosis in hemodialysis patients. The treatment brings 3.7 g (161 mmol) of sodium. How to counterbalance this sodium load was studied.Design, setting, participants, & measurements: Plasma conductivity (Cp) and mass balance index were compared for 20 sessions without thiosulfate and 20 sessions with thiosulfate infusion. Subsequently, the dialysate conductivity was set to 13.8 mS/cm during the entire session. Next, dialysate conductivity was set to 14 mS/cm for the first 3 h and to 13 mS/cm for the last hour of thiosulfate infusion (n = 25).Results: The Cp variation between beginning and end was equal to +0.005 ± 0.13 mS/cm without thiosulfate, +0.24 ± 0.13 mS/cm with thiosulfate, and 14 mS/cm dialysate conductivity (P < 0.001). The decrease in dialysate conductivity at 13.8 mS/cm did not counterbalance the sodium load. The last program adequately compensated the sodium load with a Cp increase of only +0.05 ± 0.14 mS/cm (NS versus without thiosulfate). The total of the dialyzed sodium and the sodium load for this last program was equal to 603 mmol compared with 456 mmol for the sessions without thiosulfate, the difference of 147 mmol being close to the known content of 161 mmol in 25 g of infused thiosulfate.Conclusions: Thiosulfate infusion requires a decrease of dialysate conductivity of −1 mS/cm during the infusion to counterbalance the added 3.7 g (161 mmol) sodium load.Sodium thiosulfate treatment has been proposed to treat calcific uremic arteriolopathy in hemodialysis patients (1–4) and recently for nephrogenic systemic fibrosis (5). The dose is 25 g/1.73 m² per hemodialysis session during the last 60 min. The formulation of sodium thiosulfate is Na₂S₂O₃·(H₂O)₅ and the infusion of this amount of thiosulfate brings a clinically significant sodium load. The calculated sodium load for 25 g of thiosulfate is 3.7 g (161 mmol), corresponding to the amount of sodium contained in 1 L of isotonic sodium chloride infusion.The two patients that underwent the thiosulfate treatment had developed severe calcific uremic arteriolopathy of the extremities. We decided to use sodium thiosulfate at a dose of 25 g per dialysis session. As we started the thiosulfate therapy, we rapidly noticed that the infusion induced a notable increase in plasma conductivity (Figure 1). Hence we recorded the plasma conductivity variation during the dialysis sessions under thiosulfate for the two patients and we modified the dialysate treatment to counterbalance the sodium load.Open in a separate windowFigure 1.Example of a plasma conductivity curve during a dialysis session with thiosulfate infusion during the last hour of dialysis. Dialysate conductivity was kept constant at 14.0 mS/cm.