fig1 and 2 schematically illustrate an exemplary embodiment of a safety device 1 which is used to monitor whether a cannula 2 , functioning as an injection body , is inserted correctly into a patient &# 39 ; s vascular access or is detached from the vascular access . the vascular access in particular can be a puncture site , wherein reference is made to this type of application without restricting the universality of the invention . the vascular access generally can also take other forms , such as a surgical cut . fig1 depicts the cannula 2 inserted at a puncture site , meaning into an arm 3 of a patient , whereas fig2 shows the cannula 2 detached from the puncture site . a tube inserted via a catheter into the blood stream can generally also be used as an injection body in place of a cannula 2 . in the present case , the safety device 1 is used for monitoring the dialysis treatment of a patient . the cannula 2 in this case is connected to a tube , not shown herein , by means of which purified blood coming from a dialysis machine , not shown herein , is thus recirculated via the cannula 2 into a vein of the patient . in the illustrated embodiment , the safety device 1 comprises a housing 4 with a therein arranged optical sensor . the housing 4 consists of an essentially cube - shaped plastic capsule which is open on the bottom . provided in one side wall of the housing 4 can be a small opening 4 a through which the cannula 2 is inserted into the housing 4 inside space . the dimensions of the housing 4 are adapted to the dimensions of the cannula 2 . thus , if the cannula 2 is inserted at the puncture site , as shown in fig1 , the region with the puncture site and the cannula tip is enclosed by the housing 4 , once the housing is placed with the open underside onto the arm 3 of the patient . the components of the optical sensor include a transmitter 6 for emitting light rays 5 and a receiver for receiving the light rays 5 , wherein these components are arranged on the inside of the housing 4 cover . the transmitter 6 and the receiver 7 are connected to an evaluation unit 8 located outside of the housing 4 . the transmitter 6 is embodied as a light - emitting diode while the receiver 7 is embodied as a photo resistor or a photo diode . the evaluation unit 8 consists of a microcontroller or the like . the optical sensor forms a light scanner for which the sensor components are dimensioned such that if the cannula 2 is correctly inserted into the puncture site , the light rays 5 emitted by the transmitter 6 , or a large share thereof , are reflected back from the puncture site , meaning from the arm 3 of the patient and the cannula 2 , toward the receiver 7 . an alarm is sounded if the cannula 2 shown in fig2 has detached itself from the puncture site , the cavity enclosed by the arm 3 and the housing 4 quickly fills with blood , so that the light rays 5 emitted by the transmitter 6 are strongly subdued by the blood . as a result , no light rays or only a reduced number of light rays will arrive at the receiver 7 . fig2 illustrates the case where the housing is filled almost completely with blood . the optical sensor distinguishes between these two cases by generating a binary output signal with two switching states . the first switching state corresponds to the error - free state where the cannula 2 is correctly inserted into the puncture site . the second switching state corresponds to an alarm signal state which indicates that blood flows from the puncture site because the cannula 2 is detached . it makes sense to use a reference value comparison to assign the signals received by the receiver 7 to one of these switching states . in a teach - in process , the actually received signals associated with an error - free case , meaning the case where the cannula 2 is inserted correctly into the puncture site , are entered into the evaluation unit 8 . these values are entered as reference values into the evaluation unit 8 . during the operating phase that follows the teach - in process , the actual receiving signal values are then compared to the reference values . if the values for the actually received signals coincide with the reference values within specified tolerance limits , the evaluation unit 8 considers this an error - free state , so that the output signal assumes the first switching state . on the other hand , if the received signals are outside of the reference value tolerance range , the output signal assumes the second switching state . the sensor output signal is emitted via an output 8 a of the evaluation unit 8 and functions , for example to trigger an optical or acoustic alarm . if the first switching signal is transmitted via the output 8 a , then the alarm transmitter remains deactivated . however , if the second switching state , meaning the alarm signal state , is transmitted via the output 8 a , the alarm transmitter is activated and triggers an optical or an acoustic alarm , thereby alarming the hospital personnel which can then provide immediate help to the patient . the arrow in fig2 represents transmission of the alarm signal from output 8 a to an alarm . it will be understood that the above description of the present invention is susceptible to various modifications , changes and adaptations , and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims .
a safety device for monitoring a vascular access location on a living being includes a housing adapted to surround the vascular access location and a sensor arranged in or on the housing to detect fluid flowing from the vascular access location into the housing .