Intra-dialytic symptoms are common among patients on maintenance hemodialysis (MHD). Adverse symptoms are associated with both hypervolemia and hypovolemia. Persistent hypervolemia causes hypertension, pulmonary edema, and congestive heart failure, and leads to higher mortality
. Compared with euvolemic patients, patients with recurrent episodes of intra-dialytic hypovolemia are at high risk of accelerated loss of residual renal function
, vascular access function loss
, brain atrophy
, mesenteric infarction
, and hence, higher morbidity and mortality
Patients with high pre-dialysis (pre-HD) fluid overload experience higher mortality risk compared with those with less pre-HD fluid burden
[1, 8, 9]. It is an important strategy to reduce pre-HD fluid burden by restricting inter-dialysis weight gain and to achieve euvolemic (dry) weight post-HD by appropriate ultrafiltration. At present there is no objective gold standard method for estimating target post-HD dry weight and clinical examination is unreliable.
Several observational studies showed that strict post-HD weight control was associated with better short term outcome
 or long term survival
, but other studies associated strict fluid control with increased morbidity and / or hospitalization
[12, 13]. These conflicting results regarding the relationship between fluid control and outcome mainly result from the lack of reliable method for the assessment of individual euvolemia with different studies used different definitions of dry weight including un-tolerated blood volume decrease or ultrafiltration limit
Bioimpedance spectroscopy (BIS) had long been used to assess human body composition and has been validated by isotope dilution methods
[15, 16] and reference body composition methods
[16–18]. Recently, Wizemann et al.
 used BIS to assess MHD patients’ fluid status, and found that patients who had 15% or more expansion of extra-cellular fluid (ECF) suffered higher mortality risk compared with those had less than 15% ECF expansion.
BIS appears to be a promising and a valuable tool in aiding dry weight estimation for MHD patients. Although detailed BIS-based dry weight estimating methods were published
[10, 19–21], and observational studies showed the potential benefits of BIS
[1, 8], it is still not clear whether long-term outcome could be improved by regular dry weight adjustment according to BIS based method.
We designed this multicenter, prospective, randomized and controlled trial to explore the effect of BIS guided fluid management on long-term outcome in MHD patients.