The function of dialysis fluid is to correct the chemical composition of the Uraemic Blood to normal physiological levels, removing excess Uraemic wastes and electrolytes in addition it is also responsible for the movement of buffering agents from the dialysate into the blood to restore the acid-base balance of Uraemic patients.
The difficulty of preventing bicarbonate and Calcium precipitating into insoluble Calcium Carbonate in the early years of dialysis led to the search for alternative buffering agent. The criteria for the subscription product for bicarbonate were first that it must be readily metabolized in the body leading to the production of base equivalents. Secondly it must be easily soluble and stable in a concentrated solution together with other electrolytes.
Calcium and Magnesium will not remain in solution with bicarbonate because of the low Hydrogen ion content. To solve this two separate concentrates are used the proportioning (delivery) system is more complex since it must mix and monitor three liquids instead of two. The A solution indicating (acidified) concentrate contains most of the Na, Ca, Mg, KCl and small amount of acetic acid to maintain pH low enough to keep the Ca, Mg in solution when mixed into dialysate. The B (bicarbonate) concentrate contains the sodium bicarbonate some systems include part of the sodium chloride as well as the B concentrate this raises the total conductivity, making it easier to monitor the concentrate.