Sodium modeling

The most serious side effects induced by hemodialysis therapy are caused by changes in sodium concentration and subsequent water shift between the intracellular and extracellular fluid compartment. Because of inadequate precision of proportioning, a certain sodium concentration and considerable error in the measurement of sodium concentration in dialysis fluid and plasma water, an error of up to 10 g in the diffusive exchange of sodium chloride remains in most dialysis sessions. Common side effects occur within this sodium balance error. Sodium modeling is a simplified mathematical method to describe quantitatively the fluid exchange in the body caused by changes in extracellular sodium concentration. It is based on fundamental physiologic properties of sodium and its permeability through the corresponding membranes. It also explains the different working mechanisms of sodium- and urea-related changes in osmolarity. Sodium modeling is a helpful tool for the illustration of the effects of changes in sodium concentration and ultrafiltration rate on sodium balance during one dialysis session. Sodium profiling is a method employed to avoid unwanted side effects of hemodialysis therapy by deliberately changing the sodium concentration in dialysis fluid during the course of a dialysis session. Clinical reports on practicing sodium profiling are unsatisfactory, involving only short trial periods in most cases. Most of the studies reported positive sodium balance with temporary decreases in intradialytic hypotension and less blood volume reduction, but with increases in thirst and body weight. To date, no validated studies with suitable control of sodium balance have been published that clearly demonstrate the long-term benefits of this mode of therapy compared with the use of constant dialysate sodium concentrations.