HIGH DIETARY SODIUM INTAKE CONTRIBUTES TO SODIUM RETENTION IN HAEMODIALYSIS PATIENTS (HD

P McLaren

Lister Hospital, Steveange

PROBLEM: In the HD population fluid intake in the interdialytic period determines IDWG but the influence of salt intake, which drives the thirst mechanism and determines the distribution of this fluid between body compartments has been neglected. Restricting fluid intake without associated restriction of salt intake may have a limited impact in preventing extracellular fluid (ECF) volume expansion and circulatory overload.

PURPOSE: We wished to study the relationship between sodium gain during a 48 hour interdialytic period, sodium loss during a subsequent haemodialysis session and their relationship to other indicators of volume change including IDWG, change in blood pressure and change in ECF volume.

DESIGN: 20 subjects were randomly selected. During the interdialytic period, we estimated salt intake (Food diaries analysed using the Compeat ä programme), IDWG, interdialytic urinary sodium. During the subsequent HD session we studied changes in blood pressure, relative blood volume (Optical density technique), extracellular fluid volume (Whole body multifrequency bioimpedance) and sodium mass balance (total dialysate collection).

FINDINGS: Full data was available on 17 patients. 9 patients were anuric. Mean IDWG was 1.29kg ±0.67 and mean weight loss on HD was 1.38kg ±0.78kg. Mean fluid and sodium intakes were 2.54L ± 0.62 and 223.1 ± 86.8 mmol/l respectively. Mean urinary sodium was 72.6 mmol ±51 mmol. Mean sodium loss on HD was 118.3 mmol ± 223. Mean total sodium mass balance was –70.7 mmol ± 245.5 mmol - negative indicating sodium retention Total sodium mass balance was correlated with change in blood pressure in patients with residual renal function (r = -0.706, p = 0.026) but not in anuric patients. The mean change on HD of ECF volume was 1.96L ±0.88L and of RBV was 7.2 % ± 5.87. There was a strong correlation between dietary sodium intake and weight gain in the anuric patients (r=0.914, p<0.001) but not in others, nor the patient group as a whole. Sodium and fluid intake were correlated (r=0.486, p<0.05). Sodium loss during HD correlated with change in RBV (r=0.493, p<0.05), and with change in ECF volume r = 0.347, p = 0.086) but not with change in mean arterial pressure.

CONCLUSION: Most HD patients have high salt intakes. Dietary salt intake has a significant influence on fluid intake and IDWG. Sodium removal on HD correlates with changes in RBV and ECF but is insufficient in most cases to overcome high sodium intake and overall sodium retention was the norm in this small study. We have ignored losses in faeces (up to 8 mmol/day) and sweat (approximately 5 mmol/day in cool climates), but including these would not significantly alter our conclusions.

RELEVANCE: Sodium intake plays a pivotal role sodium mass balance. Net zero sodium balance is difficult in the absence of dietary salt restriction in especially in anuric patients.