Abstract: Disclosed is a device for continuing detecting blood parameters. The device includes a catheter adapted to be introduced into the artery of a patient. A sensor is arranged in the catheter. A tube us adapted to be coupled to a vein of a patient and is also connected to the first catheter. A device controllably maintains blood flow across the sensor, the device being controlled such that initially the flow of blood to the first catheter via the tube is prevented so long as the detective blood parameters indicated a sufficient amount of fresh arterial blood is flowing around the sensor. In the event that a detective blood parameters indicate that an insufficient amount of blood flows around the sensor, then blood flow through the first catheter to the vein of the patient via the tube is then established.