If you feel your in the vein try turning the head of the transducer till you will see the vein in different axis. You will eventually see the needle entering the vein. It also sometime helps you see your vein and valves which may be obstructing your wire. Just turn the transducer slowly and you can tell the difference in the vein versus arteries the same way by the collapsing technique. If you can get use to it by using it this way it give you a better picture of catheter to vein but it is not easy and not all vein are clearly visible due to large arteries over them.