Device and method for detecting the recirculation during an extracorporeal blood treatment

A device and method for detecting recirculation for an extracorporeal blood treatment apparatus and an apparatus with a device for detecting recirculation are based on targeted haemodilution by administration of a substituate bolus, causing a pressure change in venous and arterial branches of the extracorporeal circuit due to a viscosity change of flowing fluid. Recirculation is detected based on detection of the pressure change. The device includes a control unit cooperating with a device for conveying blood and a device for supplying substituate. The control unit provides an operating mode for detecting recirculation, in which blood flow rate is reduced during administration of a substituate bolus. With simultaneous substituate bolus administration and reduction of blood flow rate, the composition of fluid flow is optimized for detection of recirculation, so that fairly large pressure changes result in venous and arterial branches, thereby improving sensitivity and reliability of the measurement method.