A machine for extracorporeal blood treatment, wherein the machine is a dialysis machine, comprising: a user interface for an extracorporeal blood treatment machine, which user interface comprises at least one screen, at least one memory comprising at least two images, at least a controller and at least one key, and a system for feedback control of the user interface comprising the controller, a sensor and a device for administration of a substance being a syringe, wherein the controller is enabled to receive input from the user interface and send instructions to the user interface; the controller is arranged to control the administration of a substance of the device; the device is monitored by the sensor; and the controller is enabled to receive input from the sensor such that the controller is enabled to provide feedback to the user interface by said instructions; characterized in that the controller is programmed for executing a method for performing a critical action, which is the syringe change, including: detecting activation of the at least one key representing the critical action, the user interface sending an input to the controller that the key has been selected, displaying on the screen a first image which in the memory is assigned to the activated key, and whereupon the controller is further programmed for: blocking the user interface until a first signal is received, wherein the sensor detects when an operator has completed a task clamping a line and opening a plunger clamp latch of the syringe, being the initial task of the syringe change critical action and sends a first signal to the controller; and upon receipt of the first signal, unblocking the user interface, and displaying on the screen a second image. a user interface for an extracorporeal blood treatment machine, which user interface comprises at least one screen, at least one memory comprising at least two images, at least a controller and at least one key, and a system for feedback control of the user interface comprising the controller, a sensor and a device for administration of a substance being a syringe, wherein the controller is enabled to receive input from the user interface and send instructions to the user interface; the controller is arranged to control the administration of a substance of the device; the device is monitored by the sensor; and the controller is enabled to receive input from the sensor such that the controller is enabled to provide feedback to the user interface by said instructions; characterized in that the controller is programmed for executing a method for performing a critical action, which is the syringe change, including: detecting activation of the at least one key representing the critical action, the user interface sending an input to the controller that the key has been selected, displaying on the screen a first image which in the memory is assigned to the activated key, and whereupon the controller is further programmed for: blocking the user interface until a first signal is received, wherein the sensor detects when an operator has completed a task clamping a line and opening a plunger clamp latch of the syringe, being the initial task of the syringe change critical action and sends a first signal to the controller; and upon receipt of the first signal, unblocking the user interface, and displaying on the screen a second image. detecting activation of the at least one key representing the critical action, the user interface sending an input to the controller that the key has been selected, displaying on the screen a first image which in the memory is assigned to the activated key, and whereupon the controller is further programmed for: blocking the user interface until a first signal is received, wherein the sensor detects when an operator has completed a task clamping a line and opening a plunger clamp latch of the syringe, being the initial task of the syringe change critical action and sends a first signal to the controller; and upon receipt of the first signal, unblocking the user interface, and displaying on the screen a second image. blocking the user interface until a first signal is received, wherein the sensor detects when an operator has completed a task clamping a line and opening a plunger clamp latch of the syringe, being the initial task of the syringe change critical action and sends a first signal to the controller; and upon receipt of the first signal, unblocking the user interface, and displaying on the screen a second image.