Sodium Balance in Maintenance Hemodialysis

Abstract

Maintenance of extracellular fluid volume balance is an essential role of chronic maintenance hemodialysis (HD). In this population, this balance is determined by salt intake during the interdialytic period and sodium removal in HD sessions. Most of the sodium in a HD session is removed by ultrafiltration of plasma water, and the diffusion process becomes responsible for the fine tuning of sodium balance. The observation of little variation in pre-HD serum sodium denotes that HD patients have an individual, stable osmolar set point. A positive dialysate-to-plasma sodium gradient is associated with increased thirst, interdialytic weight gain, and hypertension. To achieve an isonatric HD session, dialysate sodium concentration should approximately match patient's serum sodium, and all sodium gained in the interdialytic period must be removed by convection. The pre-HD serum sodium concentration may be used as a reference for dialysate sodium prescription in chronic HD. In this article, we also discuss new aspects of sodium balance, with particular attention to new observations on nonosmolar interstitial sodium storage.

Significance of Interdialytic Weight Gain versus Chronic Volume Overload: Consensus Opinion

“…(4) IDWG and sodium intake: Dietary salt restriction [22,24,58,59,60,61] can effectively reduce the IDWG, and lowering of the DNa concentration also has an effect [62,63,64,65,66,67], since dialysate-to-SNa concentration gradients are associated with IDWG [68,69,70,71]. The amount of IDWG associated with the isolated DNa prescription is small however, because the SNa component of the dialysate-to-SNa concentration gradient also contributes to IDWG (discussed below).…”

Influence of Hemofiltration on Intradialytic Plasma Volume Decrease

“…Intradialytic albumin loss and intradialytic Na change may also influence IPVD by affecting inward oncotic and osmotic forces [17, 20]; intradialytic albumin loss will facilitate IPVD by decreasing inward oncotic force, while intradialytic Na gain will prevent IPVD by increasing inward osmotic force. In the present study, intradialytic Na change in ol-HDF did not differ from the change in HD.…”

Sodium Prescription in the Prevention of Intradialytic Hypotension: New Insights into an Old Concept

“…Dialysis patients tend to maintain their own sodium setpoint increasing the water gain to balance the excess in dietary sodium that cannot be decreased by urine output. For example, a sodium intake of 8 g per day needs the intake of 1 L of water to maintain the sodium setpoint [9]. Nonetheless, the use of the sodium setpoint has its drawbacks: the correlation between salt intake and thirst is not a constant in a dialysis patient because osmoreceptors function may be impaired and because the setpoint does not consider the hypotonic hyperhydration due to the osmotic burden unrelated to sodium [10].…”