The present invention relates to a blood treatment device with at least one extra-corporeal blood circuit with a filter element and with at least one centrifugal pump means, wherein furthermore a monitoring means is provided, by means of which the flow resistance of the extracorporeal circuit can be determined, wherein the flow resistance can at least partly be determined with reference to the flow in at least one portion of the extracorporeal blood circuit and the speed of the centrifugal pump means. Furthermore, the present invention relates to a monitoring means for a blood treatment device and to a method for operating a blood treatment device.