Apparatus for extracorporeal blood treatment

An apparatus for extracorporeal blood treatment comprising:

• a filtration unit having a primary chamber and a secondary chamber separated by a semi-permeable membrane;
• a blood circuit including a blood withdrawal line connected to an inlet of the primary chamber and a blood return line connected to an outlet of the primary chamber, said blood withdrawal line and blood return line being configured for connection to a patient cardiovascular system;
• a dialysis supply line including at least one infusion line connected to said blood circuit;
• a dialysis effluent line connected to an outlet of the secondary chamber;
• a preparation device configured to prepare dialysis fluid, the preparation device in fluid communication with the dialysis supply line;
• a regulator configured to regulate a composition of the dialysis fluid;
• and
• a control unit in communication with the regulator, the control unit configured to run at least a hemofiltration (HF) treatment or a hemodiafiltration (HDF) treatment, each of said treatments including an infusion of substitution fluid through said infusion line, the control unit being programmed for receiving a value of a first parameter for an isoconductive dialysis, the first parameter being chosen from a group consisting of a concentration of at least one substance and a conductivity, wherein said control unit is configured for:
• calculating the value of a second parameter of the blood, said second parameter being a concentration of at least one substance in the blood, wherein the step of calculating the value of the second parameter is performed as a function of a main contribution term based on the first parameter and as a function of an offset contribution term based on a concentration of at least one substance in the dialysis fluid chosen from a group consisting of bicarbonate, potassium, acetate, lactate, citrate, magnesium, calcium, sulphate, and phosphate,
• storing the second parameter value in a memory connected to the control unit,
• setting a third parameter value for the dialysis fluid in the dialysis supply line at a set point based on the second parameter, said third parameter of the dialysis fluid being a conductivity of the dialysis fluid or a concentration of at least one substance in the dialysis fluid, and
• causing the regulator to regulate the conductivity of the dialysis fluid or the concentration of at least one substance in the dialysis fluid at the set point,
• wherein the main contribution term affects the second parameter for at least 80% of the second parameter value, the offset contribution term contributes to the second parameter for less than 20% of the second parameter value, and wherein the sub-step of calculating the second parameter value as a function of the main contribution term and the offset contribution term is a sub-step of calculating an algebraic sum of at least the main contribution term and the offset contribution term, and
• wherein the control unit is configured to calculate the offset contribution term as a function of a difference in concentration of at least one substance in the dialysis fluid and the same substance in the plasma, said substance being chosen from a group consisting of bicarbonate, potassium, acetate, lactate, and citrate.