Effect of lowering dialysate sodium concentration on interdialytic weight gain and blood pressure in patients undergoing thrice-weekly in-center nocturnal hemodialysis: a quality improvement study

BACKGROUND

Patients on in-center nocturnal hemodialysis therapy typically experience higher interdialytic weight gain (IDWG) than patients on conventional hemodialysis therapy. We determined the safety and effects of decreasing dialysate sodium concentration on IDWG and blood pressure in patients on thrice-weekly in-center nocturnal hemodialysis therapy.

STUDY DESIGN

Quality improvement, pre-post intervention.

SETTINGS & PARTICIPANTS

15 participants in a single facility.

QUALITY IMPROVEMENT PLAN

Participants underwent three 12-week treatment phases, each with different dialysate sodium concentrations, as follows: phase A, 140 mEq/L; phase B, 136 or 134 mEq/L; and phase A(+), 140 mEq/L. Participants were blinded to the exact timing of the intervention.

OUTCOMES

IDWG, IDWG/dry weight (IDWG%), and blood pressure.

MEASUREMENTS

Outcome data were obtained during the last 2 weeks of each phase and compared with mixed models. The fraction of sessions with adverse events (eg, cramping and hypotension) also was reported.

RESULTS

IDWG, IDWG%, and predialysis systolic blood pressure decreased significantly by 0.6 ± 0.6 kg, 0.6% ± 0.8%, and 8.3 ± 14.9 mm Hg, respectively, in phase B compared with phase A (P < 0.05 for all comparisons). No differences in predialysis diastolic and mean arterial or postdialysis blood pressures were found (P > 0.05 for all comparisons). The proportion of treatments with intradialytic hypotension was low and similar in each phase (P = 0.9). In phase B compared with phase A, predialysis plasma sodium concentration was unchanged (P > 0.05), whereas postdialysis plasma sodium concentration decreased by 3.7 ± 1.9 mEq/L (P < 0.05).

LIMITATIONS

Modest sample size.

CONCLUSION

Decreasing dialysate sodium concentrations in patients undergoing thrice-weekly in-center nocturnal hemodialysis resulted in a clinical and statistically significant decrease in IDWG, IDWG%, postdialysis plasma sodium concentration, and predialysis systolic blood pressure without increasing adverse events. Prolonged exposure to higher than required dialysate sodium concentrations may drive IDWG and counteract some of the purported benefits of "go-slow" (longer session length) hemodialysis.

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.

Hyperosmolar sodium chloride, p38 mitogen activated protein and cytokine-mediated inflammation

Although there is increasing clinical evidence that high salt intake contributes to cardiovascular events and deaths seemingly independent of hypertension, the molecular mechanism for increased atherogenesis remains unclear. Vessel wall inflammation secondary to proinflammatory cytokines is one mechanism for atherogenesis. The role of mitogen activated protein kinase (MAPK) p38 in cytokine production such as IL-1, TNF-alpha, and IL-8 are well established. The link between inflammation and salt intake likely includes p38 MAPK as hyperosmolar sodium chloride triggers phosphorylation of p38 MAPK and stimulates gene expression and synthesis of proinflammatory cytokines. Hence a possible link of high salt intake, inflammation, and atherogenesis may be one molecular mechanism for the association of high salt intake and cardiovascular events.

The internist's role in treating hypertension in hemodialysis patients

Hypertension in hemodialysis patients is typically treated with a combination of volume removal with dialysis--although limited by current dialysis paradigms--and hypertension medications. Unfortunately, most patients treated in this manner remain hypertensive. This contrasts with superior results obtained in clinical studies in which salt restriction and augmented dialytic volume removal normalized blood pressure without requiring medicines. These results are consistent with the role of excess volume as the main etiology of hypertension in end-stage renal disease (ESRD). Interdialytic blood pressure is now recognized as important to patient prognosis. These measurements are frequently obtained by internists at office visits. Internists and nephrologists should address both peri-dialysis and interdialysis hypertension in a collaborative manner. This strategy should focus on, as much as reasonably possible, salt restriction and dialytic volume removal rather than hypertension medicines.