Abstract: A device and method for invasive blood pressure measurement in a vascular access under continuous blood flows in a treatment device in extracorporeal detoxification methods is provided. Systemic arterial pressure is directly measured using an existing vascular access for dialysis, or in which the systemic arterial pressure and the temporal progression of such pressure are determined indirectly. A valve-controlled bypass system which goes around a blood pumping unit is provided so that the blood flow in the treatment device is not interrupted, and alarms are suppressed The bypass module is easily connectable to measuring equipment on various treatment units without having to adjust the same.