Dialysate sodium and sodium gradient in maintenance hemodialysis: a neglected sodium restriction approach?

Background. A higher sodium gradient (dialysate sodium minus pre-dialysis plasma sodium) during hemodialysis (HD) has been associated with sodium loading; however, its role is not well studied. We hypothesized that a sodium dialysate prescription resulting in a higher sodium gradient is associated with increases in interdialytic weight gain (IDWG), blood pressure (BP) and thirst. Methods. We conducted a cross-sectional study on 1084 clinically stable patients on HD. A descriptive analysis of the sodium prescription was performed and clinical associations with sodium gradient were analyzed. Results. The dialysate sodium prescription varied widely across dialysis facilities, ranging from 136 to 149 mEq/L, with a median of 140 mEq/L. The mean pre-HD plasma sodium was 136.7 +/- 2.9 mEq/L, resulting in the majority of subjects (n = 904, 83%) being dialyzed against a positive sodium gradient, while the mean sodium gradient was 4.6 +/- 4.4 mEq/L. After HD, the plasma sodium increased in nearly all patients (91%), reaching a mean post-HD plasma sodium of 141.3 +/- 2.5 mEq/L. We found a direct correlation between IDWG and sodium gradient (r = 0.21, P < 0.0001). After adjustment for confounders and clustering by facilities, the sodium gradient was independently associated with IDWG (70 g/mEq/L, P < 0.0001). There were no significant associations among sodium gradient and BP, whether measured as pre-HD systolic (r = -0.02), diastolic (r = -0.06) or mean arterial pressure (r = -0.04). Post-HD thirst was directly correlated with sodium gradient (r = 0.11, P = 0.02). Conclusion. Sodium gradient is associated with statistically significant and clinically meaningful differences in IDWG in stable patients on HD.