Background: Although a higher dialysate sodium concentration (DNa) is frequently used to improve haemodynamic stability during haemodialysis, few studies have compared ionic mass balance (IMB) during different DNa. Moreover, DNa is usually a standard prescription, whereas inter-individual pre-dialytic serum sodium levels may differ widely. The aims of the study were to assess IMB and the decline in blood volume (DeltaBV) during isovolaemic HD as well as during HD combined with ultrafiltration (UF) during DNa , DNa , and an individualized DNa [ind], in which DNa is equal to pre-HD plasma conductivity x 10.
Methods: IMB and plasma conductivity were assessed by on-line conductivity measurements (Diascan; Hospal) in 13 HD patients. After 1 h of isovolaemic HD, measurements were continued during UF+HD until dry weight. DeltaBV was assessed by an optical method (Hemoscan).
Results: During isovolaemic HD with DNa  and , Pre-Na was significantly related to IMB (r=0.83 and r=0.61; P<0.05). Diffusive Na flux into the patient occurred when the difference between DNa and pre-dialytic serum sodium was larger than 5 mmol/l. During UF+HD, IMB was 318+/-166 mmol during DNa , 277+/-116 mmol during DNa [ind], and 239+/-111 during DNa  (mean+/-SD; P<0.05 compared with the other treatment modalities) whereas DeltaBV did not differ significantly. In the five patients with a pre-dialytic sodium concentration below 140 mmol/l, ionic removal was significantly higher during DNa [ind] (324+/-87) compared with DNa  (228+/-127 mmol; P<0.05) without a significant difference in DeltaBV (-9.7+/-1.6 vs -7.8+/-2.3%).
Conclusion: A large difference in IMB was observed between DNa 144 and DNa 140, without a significant difference in DeltaBV. In patients with low pre-dialytic serum sodium levels, diffusive ionic influx from the dialysate into the patient may occur. In patients with low pre-dialytic sodium levels, DNa [ind] leads to an enhanced ionic removal compared with DNa  without large differences in DeltaBV.