Connection test for blood treatment machines

A control device for a blood treatment machine, wherein the blood treatment machine comprises:

• an extracorporeal blood flow circuit with first and second access devices for connection to upstream and downstream portions, respectively, of a vascular access of a patient and having a blood pump operable to generate a flow of blood in the extracorporeal blood flow circuit from one of the first and second access devices through a blood compartment of a dialyzer and to another of the first and second access devices;
• and
• a treatment fluid flow circuit configured to generate a flow of treatment fluid through a treatment fluid compartment of the dialyzer, said treatment fluid compartment being separated from the blood compartment by a semi-permeable membrane,
• wherein said control device is configured to, during a connection test:
• cause the blood treatment machine to switch between a first operating state in which the blood pump is operated in a default direction to pump the blood from the first access device through the blood compartment of the dialyzer to the second access device, and a second operating state in which the blood pump is operated in a reverse direction to pump the blood from the second access device through the blood compartment of the dialyzer to the first access device,
• acquire an output signal of at least one sensor in the blood treatment machine,
• compute, based on the output signal, an efficiency change parameter that represents a change in in-vivo clearance of the blood treatment machine during the switch of the blood treatment machine between the first and second operating states, and
• evaluate the efficiency change parameter to determine if the first or second operating state involves a dual fault condition comprising both a co-current dialyzer configuration, in which the flow of blood through the blood compartment and the flow of treatment fluid through the treatment fluid compartment are in a common direction along the semi-permeable membrane, and a reversed access device configuration, in which the first and second access devices are connected to the downstream and upstream portions, respectively, of the vascular access.