Cannulation techniques. Artwork showing various veins and a range of cannulation techniques used to insert needles and tubes into veins. A cannula is a tube inserted into the vein of a patient, through which various drugs can be administered. The general term for puncturing a vein is venepuncture. A healthy vein is at left. The vein at centre left is swollen and had a regular series of puncture marks indicating treatment of the entire vein. The vein at centre right has punctures in the two large distensions (top and bottom) that are typical of conditions such as varicose veins. The vein at right has two punctures typical of normal drug delivery or blood sampling.