[Assessment of salt intake in hemodialysis]

One of the main goals of dialysis is to reach a correct sodium balance. Dietary sodium restriction facilitates control of thirst, water overload, hypertension and cardiac failure. Nowadays, it is possible to estimate sodium mass transfer and known interdialytic salt intake, by means of non-invasive methods. The use of dialysate sodium profiles improves dialysis tolerance but it has been reported that interdialytic thirst may increase because of an inappropriate sodium balance. The aim of this study was to evaluate the usual salt intake in hemodialysis patients, the effects on interdialytic gain weight, arterial pressure, blood volume preservation and dialysis tolerance of two different profiles of dialysate sodium and an additional session with salt restriction. Seventeen dialysis patients, 12 male and 5 females, were studied. Each patient underwent seven hemodialysis treatments: three consecutives sessions (a week) with constant sodium and ultrafiltration hemodialysis; three consecutive sessions with exponential decrease of conductivity (Initial 15.5-16.0, mid-session 14.3 and at the end 13.9-14 mS/cm) and ultrafiltration (1.6 l/h initial and 0.1 at the end) profiled hemodialysis; and an additional session which had a special dietary salt restriction. Dialysis parameters and dry weight were kept constant. Integra monitor with Diascan and Hemoscan biosensors (Hospal) were used in all sessions. We measured pre- and postdialytic plasma conductivity, sodium mass transfer, interdialytic weight gain, mean arterial pressure (MAP), percent reductions of blood volume (%R-BV) and hypotensive episodes during dialysis. Mean sodium mass transfer was 1,144 +/- 356 mmol (no profile week) vs 1,242 +/- 349 mmol (week with profiles), NS. It was equivalent to a salt ingestion of 9.6 +/- 3 and 10.4 +/- 3 g/day respectively. End plasma conductivity was 14.04 +/- 0.14 (no profile) versus 14.21 +/- 0.08 mS/cm (profiled), p < 0.001. Interdialytic weight gain was 2.49 +/- 0.76 (no profile) vs 2.32 +/- 0.56 kg (profiled), NS. MAP was 101 +/- 11 (no profile) vs 99 +/- 10 mmHg (profiled), NS. The %R-BV was -7.73 +/- 3 (no profile) vs -6.46 +/- 3% (profiled), p < 0.01. Hypotensive episodes/session were 0.66 +/- 0.75 (no profiles) vs 0.41 +/- 0.57 (profiled), NS. Mean sodium mass transfer was 356 +/- 125 mmol with usual salt intake and 240 +/- 81 mmol with salt restriction, p < 0.001. It was equivalent to a salt ingestion of 10.47 +/- 3 versus 7.06 +/- 2 g per day respectively, p < 0.001. Initial plasma conductivity was 14.31 +/- 0.21 (usually sodium intake) versus 14.16 +/- 0.17 mS/cm (salt restriction), p < 0.01. Predialysis blood pressures were decreased with dietary salt restriction, MAP was 99.1 +/- 11 vs 94.4 +/- 12 mmHg (p < 0.01). Interdialytic weight gain decreased with salt restriction, 2.32 +/- 0.76 vs 1.78 +/- 0.49 kg (p < 0.001). The %R-BV was -7.25 +/- 2 (usual sodium intake) vs -5.91 +/- 2% (salt restriction), p < 0.01. Hypotensive episodes/session were 0.71 +/- 0.8 (usual sodium intake) vs 0.18 +/- 0.5 (salt restriction), p < 0.05. In conclusion, automatic measurement of sodium mass transfer is a practical tool to follow dietary salt ingestion in hemodialysis patients. It allows us accurate, individualised and continual dietary interventions. The use of exponential decrease sodium profiles improve dialysis tolerance without changes in sodium balance, interdialytic weight gain or arterial pressure. A reduction of three g in salt intake observed in this study was beneficial in interdialytic weight gain, dialysis tolerance and blood pressure control.