title: Sodium setpoint and sodium gradient: influence on plasma sodium change and weight gain.
abstract: OBJECTIVE
  In hemodialysis and hemodiafiltration patients, the plasma sodium (PNa) measured before dialysis can be regarded as the sodium setpoint. By the end of dialysis, the PNa typically approximates the prescribed dialysate sodium (DNa), the difference between DNa and PNa being considered the sodium gradient. We determined the relationship between setpoint, gradient and pre- to postdialysis PNa change (delta PNa), and studied associations with dialysis-related variables.
  
  
  METHODS
  Cohort study. Measurements from 132 patients during 12 consecutive treatments included PNa and DNa concentrations, pre- to postdialysis body weight and predialysis systolic blood pressure.
  
  
  RESULTS
  Sodium setpoints were normally distributed (137.9 ± 2.4 mmol/l), DNa prescriptions were non-normally distributed (138.9 ± 1.8 mmol/l). The sodium gradient correlated strongly with delta PNa (r = 0.76, p < 0.001). Both sodium gradient and delta PNa correlated with relative interdialytic weight gain (IDWG; r = 0.25, p = 0.004, and r = 0.44, p < 0.001, respectively), but not with predialysis systolic blood pressure. These correlations were consistent after exclusion of patients with urine volume >500 ml/day and patients undergoing sodium profiling, and increased after exclusion of patients with hemodiafiltration protocols. Predictors for having higher relative IDWG (≥2.8%) were delta PNa concentrations ≥0 mmol/l and younger age. Predictors for having a delta PNa concentration ≥0 mmol/l were lower sodium setpoints, higher DNa prescriptions, use of Nikkiso machines, sodium profiling and younger age. Patients with positive delta PNa despite negative gradients were significantly younger, used more Nikkiso machines and presented with higher IDWG.
  
  
  CONCLUSIONS
  IDWG correlated with the sodium gradient and more strongly with delta PNa, suggesting the need for studying other outcomes, such as morbidity and mortality.
authors.affiliation: Department of Medicine III, Medical University of Vienna, Austria. manfred.hecking@meduniwien.ac.at
authors.forename: Manfred
authors.initials: M
authors.lastname: Hecking
authors.forename: Alexander
authors.initials: A
authors.lastname: Kainz
authors.forename: Walter H
authors.initials: WH
authors.lastname: Hörl
authors.forename: Harald
authors.initials: H
authors.lastname: Herkner
authors.forename: Gere
authors.initials: G
authors.lastname: Sunder-Plassmann
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001835:Body Weight; D015314:Dialysis Solutions; D005260:Female; D017583:Hemodiafiltration / Q000379:methods; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy; D008297:Male; D006435:Renal Dialysis / Q000379:methods; D012964:Sodium / Q000097:blood* / Q000378:metabolism*; D015430:Weight Gain
chemical_list: D015314:Dialysis Solutions; D012964:Sodium