Title:
Gradient between predialysis plasma sodium and prescribed sodium dialysate: a cross-sectional study in a large cohort of hemodialysis patients.

Chazot Charles¹ ;Chazot Charles¹ ;Chazot Charles¹ ;Chazot Charles¹ ;Chazot Charles¹ ;Chazot Charles¹ ;Chazot Charles¹ ;Chazot Charles¹

1. Centre de Rein Artificiel Tassin France

E-mail address corresponding author:
chchazot@club-internet.fr

Background:
Sodium concentration in dialysate is usually set at a fixed level. Even if sodium modelling is sometimes used to decrease dialysis side effects, individualization of sodium dialysate concentration is not as widely used as for potassium or calcium concentrations. In our unit the usual prescribed sodium concentration in dialysate is 138 mmoles/l. However, a significant plasma-dialysate (P-D) sodium gradient may have important consequences on sodium balance and may influence interdialytic weight gain and blood pressure control. We have cross-sectionally studied these parameters in a large cohort of hemodialysis (HD) patients and analyzed the factors associated with the P-D sodium gradient..

Methods:
In April 2005, 189 hemodialysis patients (age:66.5±14,9 y.o, HD vintage:73,1±85,9 months, session time:6,5±1,3 hours, F/M:74/115, diabetes:47/189) treated 3 times a week (Hd1-Hd2-Hd3) were prescribed sodium dialysate concentration of 138 mmoles/l on Fresenius 4008 stations. These patients have undergone pre and post-dialysis plasma sodium assessment at a mid-week session (Hd2). We have calculated the gradient between predialysis plasma and dialysate prescribed sodium concentration, and analyzed the factors that are associated with this gradient and its relationship to interdialytic weight gain and predialysis blood pressure.

Results:
The average P-D sodium gradient was -3,05±2,85 mmoles/l. It was not correlated with age or dialysis vintage and not associated with HD session length. No significant difference was found between male and female patients. Diabetic patients had a higher P-D gradient (-4,7± 2,5 vs -2,5± 3,2mmoles/l, p<0,0001). The P-D sodium gradient was negatively correlated with the interdialytic weight gain between Hd1 and Hd2 expressed in kilograms (kgs) (r=0,257, p=0,0006) and in body weight % (r=0,253, p=0,0007) and between Hd2 and Hd3 (kgs, r=0,263,p=0,0004; %,r=0,256,p=0,0006). No correlation was found with Hd2 and Hd3 predialysis mean arterial pressure.

Conclusion:
These data show a higher P-D sodium gradient in diabetic patients. Thirst stimulation by hyperglycemia may be one of the explanations. We have found also a relationship between P-D sodium gradient and interdialytic weight gain. As this relationship exists all along the week, it can be speculated that water intake may induce relative hyponatremia, but also that this gradient and subsequent sodium load from dialysate during the session may induce thirst and increased water intake. The consequences of the individualization of sodium prescription on interdialytic weight gain remain to be studied.

Subject:
Hemodialysis

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