Prior to performing the procedure, the intended target vein should be identified and confirmed first in the transverse plane and then in the longitudinal plane On ultrasound, veins are characterized by their easy compressibility, color flow, and Doppler waveforms Placing gentle pressure on the probe, the walls of vein should collapse In contrast, arteries will pulsate and the walls of the arteries will resist collapsing when compressed ( Videos 131.21 and 131.22 ) Both veins and arteries have characteristic patterns when assessed with color Doppler ( Video 131.23 ) Once the vein is identified, the depth to the center of the vein should be measured When the needle is inserted into the skin, it is traveling along the hypotenuse of a right triangle, and the distance it must traverse before hitting the vein should be calculated In the static approach, once the vasculature and surrounding anatomy are imaged, the position of the vein should be marked on the skin at two points along the path of the vessel The ultrasound probe is then set aside and the procedure continues using the landmarks identified with ultrasound, but without active ultrasound assistance This method does improve success rates, although complications are reduced further when using dynamic ultrasound The dynamic method uses ultrasound in real time to visualize the needle puncturing the vein It is important that the ultrasound machine be positioned in front of the proceduralist, making direct visualization possible The transducer marker should face to the left, the same direction as the marker on the screen This is critical when redirecting the needle; as the needle is moved toward the left of the probe, it moves toward the left side of the screen