Blood purification device having an extracorporeal blood circuit with a blood inflow and outflow to and from a dialysis unit, wherein the dialysis unit comprises a dialysis solution inflow and a dialysate outflow, characterized by a control loop for control of the acid-base equilibrium of the blood, wherein bicarbonate is supplied to the blood using an aqueous bicarbonate-containing solution, wherein a measuring means for measuring a blood buffer parameter is associated with the control loop, wherein the blood buffer parameter is selected from one of bicarbonate concentration and CO2 partial pressure, and wherein a signal corresponding to the measured value of the blood buffer parameter can be supplied to a closed-loop control apparatus, which regulates the value of the blood buffer parameter by the supply of bicarbonate, and at least one pH-measuring means, wherein a signal corresponding to the pH value can be supplied to an alarm apparatus.