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 withdrawal line in fluid communication with an inlet of the primary chamber;
• a blood return line in fluid communication with an outlet of the primary chamber, the blood lines configured for connection to a patient cardiovascular system;
• a dialysis supply line in fluid communication with an inlet of the secondary chamber;
• a dialysis effluent line in fluid communication with an outlet of the secondary chamber;
• a preparation device for preparing dialysis fluid, the preparation device in fluid communication with the dialysis supply line and comprising a regulating device for regulating composition of the dialysis fluid;
• a sensor for measuring a parameter value of dialysate in the dialysis effluent line, the parameter value of the dialysate being at least one chosen from a group consisting of:
• (i) conductivity of the dialysate;
• (ii) a conductivity-related parameter of the dialysate;
• (iii) concentration of at least a substance in the dialysate;
• or (iv) a concentration-related parameter of at least a substance in the dialysate;
• and
• a control unit communicating with the sensor to receive the parameter value of the dialysate, the control unit further communicating with the regulating device and calculating a value representative of plasma conductivity, wherein the control unit is configured for:
• setting a parameter value for dialysis fluid in the dialysis supply line at an initial set point, the parameter value of the dialysis fluid being at least one chosen from a group consisting of:
• (i) conductivity of the dialysis fluid;
• (ii) a conductivity-related parameter of the dialysis fluid;
• (iii) concentration of at least a substance in the dialysis fluid;
• or (iv) a concentration-related parameter of at least a substance in the dialysis fluid;
• after setting the parameter value of the dialysis fluid at the initial set point, circulating the dialysis fluid through the secondary chamber of the filtration unit so as to exchange with blood;
• circulating blood through the primary chamber of the filtration unit;
• measuring at least an initial parameter value of the dialysate downstream of the secondary chamber at the beginning of the treatment;
• and
• calculating, based on the measured initial value and on a corresponding parameter value of the dialysis fluid in the dialysis supply line, an initial plasma conductivity,
• wherein the circulating of the dialysis fluid through the secondary chamber up to the measuring of the initial value used for calculating the initial plasma conductivity is performed while maintaining the parameter value of the dialysis fluid to be substantially constant.