Placing a catheter. Artwork showing the placement of a catheter in a patient's blood vessel. A hypodermic needle is being inserted at an angle of 25 degrees (centre left). The inset diagram (upper right) shows the needle being threaded along the lumen of the blood vessel. Once inserted in the blood vessel, the needle will be taped to keep it in place. Here, the catheter will be used as a shunt, a device used to drain excess fluid. Catheters can also be used to administer drugs.