Abstract: The device for use with a catheter includes a sleeve 21 for assembly onto the shaft of a catheter 1, between the catheter shaft and a Tuohy-Borst connector 3. The internal diameter of the sleeve 21 is complementary with the external diameter of the catheter 1 so that the catheter is movable within the sleeve. The external diameter of the sleeve is such that when the Tuohy-Borst connector is closed, a seal is formed between the sleeve and the connector. A flange 24 is provided at one end of the device for engagement with the connector, to prevent movement of the sleeve with the catheter. The internal diameter of the sleeve 21 is also complementary with the external diameter of the catheter 1 so as to provide an annular space about the catheter whereby, in use, a controlled amount of backbleed of blood is allowed.