P1081DIALYSATE SODIUM ALLIGNMENT AND SODIUM SET-POINT STABILITY IN HEMODIALYSIS PATIENTS: TWO-YEAR OBSERVATION

Background and Aims The low dialysate sodium (NaD) reduces intradialytic weight gain (IDWG) and blood pressure (BP), which are associated with improved outcomes. However, the intervention probably also increases intradialytic hypotension and reduces serum sodium (NaS), that are associated with increased mortality risk, so NaD should be individualized and brought closer to NaS. Predialysis natraemia in hemodialysis (HD) patients is considered constant (set-point) but some observations contradict this statement. The significance of clinical parameters, dialysis parameters and body water distribution is not clear. Method We undertake the retrospective observation among 45 HD patients for 24 months before large-scale prospective intervention investigation for individualization of NaD. We used two-year routinely monthly fixed data: NaS, NaD, IDWG, frequency of intradialysis hyper- and hypotension and seizures, peri- and intradialysis BP, home BP estimates, clinically and by bioimpedance estimated dry weight, ultrafiltration rate, frequency and duration of HD sessions. Results We included 27 males and 18 females of 60 (34-83) years old, with median HD vintage of 63 (29÷93) months. 1048 NaS measurements revealed mean natraemia of 137.1±2.8 (Q5-Q95 132-141) mmol/l (corrected for glucose). No differences in mean NaS according to gender, age, HD vintage, cardiac or liver dysfunction and residual renal function were found. Intraindividual NaS mean varied from 132 to 141 mmol/l and median of coefficient of variation (CV) was 1.4% (1.2÷1.6) (range 0.9-2.0%) which could be attributed mainly to measurement accuracy. The intraindividual NaS Q10-Q90 did not exceed 6 mmol/l with its median 3.0 (2.7÷3.7). Among whole group we revealed slow decreasing NaD trend (-0.12 mmol/l per year, R?0.45) which was accompanied by more prominent trend in systolic BP (-3.3 mmHg/year, R?0.64) and diastolic BP (-1.6 mmHg/year, R?0.49). In parallel, the frequency of intradialytic hypotension increased by 1.6 episodes/100HD per year (mean 2.3±0.6 after excluding the trend). 33 patients (73%) showed no significant individual trend in NaS (<1 mmol/l per year) for 24 months, 8 (18%) demonstrated decreasing trend (mean -1.5 mmol/l per year) while only 4 (9%) - increasing trend (mean +1.6 mmol/l per year). We observed no trend in prescribed bicarbonate level in dialysate. There were no significant associations between intraindividual deviations from individual mean weight before HD and from mean individual NaS. In whole group, intraindividual variations in NaS had no link with mean NaS. We observed the significant variations in NaS only in patients with large CV of predialysis weight (Q90-Q10>5 kg over 2 years). Overall mean of sodium serum to dialysate gradient (NaG) was slightly positive (+0.15±3.0 mmol/l) while 58% of patients had negative or neutral NaG. The latter had lesser IDWG but no difference in intradialytic hypotension frequency. We evaluated the number of random consecutive monthly predialysis NaS need to get acceptable estimation of real mean two-year predialysis NaS: five values gave 94% hit in range -1÷ +1 mmol/l. Conclusion Serum sodium is stable over time in HD patients with the only exception of patients with large intraindividual predialysis weight variation. Pre-HD serum sodium may be used as a parameter for individualizing dialysate sodium prescription.