Clinical Validation of a Predictive Modeling Equation for Sodium

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Abstract
Changes in plasma Na concentration during hemodialysis were predicted by changes in Na concentration of the dialysate at equilibrium with the plasma, according to the formula C''t = CD- (CD - C''0) [(V0 - QFt)/V0]A/QF, where C''0 and C''t are the Na concentration of the dialysate at equilibrium with the plasma at times 0 and t, respectively; QF is the ultrafiltration flow rate; V0 is the initial total body water; and CD is the Na1 dialysate concentration. This modeling involves only 1 parameter, A, which is the effective Na dialysance and depends on the dialyzer, the QF, the plasma water flow rate and the actual Donnan coefficient. Parameter A was evaluated after 1 h of dialysis. Seven routine 4-h dialysis sessions were performed in which the Na concentration of dialysate at equilibrium with the plasma was measured at varying times. The mean (.+-. [standard error of the mean]) difference between predicted and measured values was .DELTA.C = 0.5 .+-. 0.2 mmol/l. These data support the validity of the model that allows the monitoring of Na dialysate concentration to obtain a prescribed Na plasma concentration at the end of a dialysis session.