Extracorporeal blood treatment device

An extracorporeal blood treatment apparatus designed for connection to a blood treatment unit that is divided by a semipermeable membrane into a first compartment, which is part of a fluid system, and a second compartment, which is part of an extracorporeal blood circuit,

• the fluid system comprising a first flow path that has at least one fluid line and is designed as a flow path for supplying a fresh treatment fluid from a fluid source to the first compartment of the blood treatment unit, and comprising a second flow path that has at least one fluid line and is designed as a flow path for discharging a used treatment fluid from the first compartment of the blood treatment unit to a drain, and
• at least one additional flow path that has at least one fluid line being provided for a special operating mode, said at least one additional flow path having an upstream portion which is upstream of a valve device that has at least one shut-off member, and a downstream portion which is downstream of the valve device and is in fluid connection with the second flow path, the valve device being designed such that a fluid connection is established between the upstream portion and the downstream portion of the at least one additional flow path for the special operating mode in a first operating position of the valve device and the fluid connection is interrupted in a second operating position of the valve device,
• a control unit for actuating the valve device such that the valve device assumes the first operating position for the special operating mode and the second operating position for another operating mode,
• wherein a pressure-based checking device is provided which interacts with the control unit and is designed such that a fluid connection between the upstream portion and the downstream portion of the at least one additional flow path for the special operating mode is only established when the pressure-based checking device detects an operating state in which it is ensured that fluid in the at least one additional flow path for the special operating mode flows towards the second flow path.