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.