The association of the sodium "setpoint" to interdialytic weight gain and blood pressure in hemodialysis patients

Hemodialysis patients lack the normal mechanisms to regulate body water volume and osmolality. The dialysis treatment is expected to adequately regulate both body water volume and body Na+ content, which is the primary action determining body water osmolality. Data in subjects with normal renal function indicate that an individual has a specific osmolality value above which thirst is generated and fluid will be ingested. This specific osmolality value or "setpoint" varies among individuals, but is quite reproducible within an individual. It was postulated that hemodialysis patients also may have a Na+ 'setpoint', which if increased by the use of higher dialysate Na+ concentration, might be associated with increased interdialytic weight gain and blood pressure. Monthly laboratory and treatment data were abstracted on 58 hemodialysis patients and included pre- and post-dialysis serum Na+ concentrations, interdialytic weight gain and blood pressure over 9 to 16 months. The Na+ concentrations were averaged to determine the individual Na+ 'setpoint' and the Na+ gradient (Dialysis Na+ concentration - mean Na+ concentration) was determined for each patient. Linear regression analyses showed that there was a statistically significant association between the magnitude of the Na+ gradient and interdialytic weight gain and blood pressure. These data suggest that interdialytic weight gain in individual patients may be associated with the use of dialysate Na+ concentration in excess of the patient's desired Na+ 'setpoint'. More individualization of dialysate Na+ concentration may be indicated.