Dialysate Sodium Control During Modeling in Hemodialysis

Abstract

Abstract: Dialysate sodium (Na+) modeling in hemodialysis requires precise individual adjustment and control of Na+ dialysate concentration. In practice, variations of Na+ concentration can be important and can affect the accuracy of Na+ modeling. Variations relate mainly to the low accuracy of dialysate concentrate (±2.5% for Na+ is tolerated by the European Pharmacopeias), purity of hemodialysis water (2.17 mEq/L is the limit fixed by the French Pharmacopeia), and precision of the proportioning delivery systems for hemodialysis bath preparation. To minimize these difficulties, this study focused on the following points: (a) Na+ concentration is maintained constant (133 mEq/L) in the dialysate manufacturing unit. In 1982, 268 dialysate preparations (177,000 L) were made, and the mean value for Na+ concentration was 133.1 ± 0.3 mEq/L with a probability of 99.9%. (b) The purity of the water, especially for Na+, Ca 2+ , and K+, is controlled for two times a day. (c) The accuracy of the proportioning delivery system is controlled by two conductivity monitors, and the variation of Na+ concentration around 133 mEq/L is smaller than ±0.5%. As the composition of the basic dialyzing fluid remains constant before adaptation, conductivity values reflect exactly Na+ variation, and are not affected by variations of other elements (K+, Ca 2+ , Mg 2+ ) that may occur when modification of the dialysate is used for Na+ modeling, (d) Na+ dialysate concentration is adapted for each patient's need by a bedside monitor with sterile Na+ solutions (5 mol/L). The additional pumps are calibrated with precision and increase gradually the Na+ dialysate concentration from 0.7 to 14 mEq/L. Two pumps can be used simultaneously. Dialyzing fluid is also adjusted for K+ and Ca 2+ with the same system. This method allows an accurate adjustment of Na+ concentration (±1%) without interference of the other elements and permits Na+ modeling for 64 patients each day. A precision of 1% or even less for Na+ concentration in the dialysate bath can be obtained in routine use, provided that special attention is focused on some parameters for the accuracy and reliability of concentration measurements. The precision of Na+ concentration in the concentrate is also of great importance, and it appears that if modeling in the future becomes widely used, a reduction of the norms required by the pharmacopeias will be necessary.