An apparatus for extracorporeal blood treatment including a treatment unit; an extracorporeal blood circuit; an infusion line of a replacement fluid; a dialysis line connected in inlet to the second chamber; a fluid evacuation line; sensors for determining a first parameter relating to a patient's blood volume (BV %), a second parameter relating to an ultrafiltration flow rate (UFR) or to a patient's weight loss rate (WLR), a third parameter (Cd, Na) relating to a conductivity or concentration of a liquid crossing the dialysis line and/or the infusion line, and a fourth parameter relating to an infusion flow rate (QINF), and a control unit performing a control procedure to determine a variation in blood volume (BV %) and perform a setting sequence, wherein the control unit regulates a transmembrane pressure (TMP) to values which enable maximising the convective exchanges.