Variations in predialytic plasma conductivity in dialysis patients: effect on ionic mass balance and blood pressure

In this study, variations in plasma conductivity (PC), as a surrogate marker of plasma sodium, as well as its relation with intradialytic ionic mass balance (IMB) and blood pressure were assessed in 73 patients. Plasma conductivity and IMB were retrieved on a treatment to treatment basis during a 6-month period. Dialysate sodium concentration was 140 mmol/L. A total of 4070 treatments were analyzed. Mean coefficient of variation for predialytic PC was 1.3%, and mean intraindividual range in predialytic PC measurements during the 6-month follow-up period was 0.9 mS/cm (plasma sodium ∼ 9 mmol/L). Predialytic PC was related to both diffusive and total IMB (r = 0.91, p < 0.001; and r = 0.35, p < 0.01). The average diffusive IMB over a 6-month period was negative in 33% of patients, and the average PC increased during dialysis in 14% of patients. Averaged predialytic PC was significantly related to systolic blood pressure (r = 0.35; p < 0.01), whereas within patients, predialytic systolic blood pressure was significantly different between treatments with the lowest and highest predialytic PC (139 ± 24 vs. 147 ± 21 mm Hg; p < 0.05). In conclusion, depending on PC, diffusive ionic transfer from dialysate to patient may occur in a significant percentage of patients using a dialysate sodium concentration of 140 mmol/L. Variations in PC are related to blood pressure, which might suggest a volume-independent effect of sodium.