Abstract: 【Abstract】Background Maintenance hemodialysis (MHD) patients are associated with higher incidence
of cardiovascular morbidity and mortality, for which the risk factors include hypertension, overhydration, etc.
More interdialytic weight gain (IDWG) usually reflects water overload in MHD patients. Sodium gradient is
defined as the difference of sodium concentration in dialysate and in predialysis serum. We hypothesize that
lower absolute sodium gradient is associated with lower IDWG, and try to figure out the correlation of sodium
gradient with water load and interdialytic hypotention in MHD patients. Methods We conducted a retrospective
study on 81 MHD patients in our hemodialysis center from Mar. to Dec. in 2013. Basic clinic data, predialysis
and postdialysis serum sodium concentrations, sodium gradient, IDWG, IDWG% (IDWG/dry body
weight×100%), and the prevalence of interdialytic hypotension were recorded and analyzed. Results The dialysate
sodium was 135 mmol/L for all patients, and the predialytic serum sodium was 138.81±3.27 (130.2～
145.0) mmol/L with the absolute sodium gradient of 3.92±2.69 (0～10.0) mmol/L. IDWG and IDWG% were
2.06±0.82 (0.50～4.20) kg, and 3.71±1.42 (1.01～8.42) %, respectively. The absolute sodium gradient was
positively correlated with IDWG (r=0.349, P=0.001) and IDWG% (r=0.269, P=0.013). The incidence of interdialytic
hypotension had no significant correlation with absolute sodium gradient and IDWG. Age was negatively
correlated with predialysis serum sodium, absolute sodium gradient, IDWG and IDWG%. Conclusions
The absolute sodium gradient was directly associated with IDWG, and higher absolute sodium gradient was
associated with higher IDWG. Individualized sodium concentration in dialysate for each MHD patient may be
useful for the prevention of overhydration in MHD patients.

Key words: Hemodialysis, sodium gradient, interdialytic weight gain