Sodium set-point in haemodialysis: is it what we see clinically?

Natraemia in haemodialysis (HD) patients is considered constant contrary to daily clinical observations. Its relationship with clinical parameters, dialysis parameters and body water (BW) distribution is not clear.

The aims of this study were to know 1) the intraindividual variability of natraemia, 2) the relationship between natraemia and clinical and dialysis parameters and 3) the relationship between natraemia and BW distribution by bioimpedance.

Observational retrospective study on 98 chronic HD patients. Clinical, HD and natraemia, glucose and bioimpedance data were collected.

We included 63 males and 35 females of 69.6 (21-91) years of age, with a follow-up of 23.2 (10) months. Variability: 1802 sodium measurements: mean natraemia 138 (3.2) mEq/l and corrected for glucose: 139.1 (3.6) mEq/l, p<.0001. Intraindividual coefficient of variation (CV) was 2% (0.8) (range 1-5.6%) and it correlated negatively with natraemia (r=-0.63, p<.0001). Clinical parameters: corrected natraemia was lower in diabetics than in non-diabetics 138 (2.4) compared with 139 (2) mEq/l, p<.003, CV 2.3 (0.9) compared with 1.9 (0.7)% (p<.01) and SD 3.2 (1.2) compared with 2.5 (0.9) mEq/l (p<.04). No differences according to gender, age, HD time, cardiac or liver disease, medication use, residual renal function or mortality were found. HD parameters: a positive relationship was found between natraemia and total dialysate conductivity and it was negative with interdialysis weight gain (IDG). - Bioimpedance: no relationship was found between natraemia and BW distribution.

Natraemia varies in each patient and is related positively with conductivity and negatively with IDG. In diabetics natraemia is lower and CV is higher. There is no relationship between natraemia and BW distribution.