The Effect of Diffusive and Convective Sodium Balance During Hemodialysis on Interdialytic Weight Gain

Patients with end stage renal disease (ESRD) often require hemodialysis treatments in which blood’s water and dissolved solutes undergo diffusion and convection by exposure to an extracorporeal membrane. The leading cause of death in this population is cardiovascular, and how hemodialysis is prescribed alters total sodium balance, a critical determinant of cardiovascular health. We performed retrospective and prospective analysis of data from patients in the Southwestern Ontario Regional Hemodialysis Program. An increased Dialysate sodium (Dial-Na+) to Pre-dialysis plasma sodium (Pre- Na+) concentration difference (DPNa+) leads to adverse clinical outcomes in hemodialysis patients. The post- to pre-dialysis plasma sodium difference (PPNa+) predicts clinical outcomes equally well as DPNa+ so long as Dial-Na+ is within 3 mmol/L of Pre-Na+. Calculation of DPNa+ requires determination of the Pre-Na+, historically thought to be stable in hemodialysis patients and thus termed “setpoint” (SP). However, we determined that SP is modifiable by hemodialysis prescription. Finally, an equation to predict interdialytic weight gain was created, confirming Dial-Na+, dialysis frequency and duration to be modifiable factors affecting IDWG. Further research is required to validate this equation prospectively, and to determine the impact of changes of SP on cardiovascular morbidity and mortality