Ultrasound-guided deep peripheral vein cannulation. The brachial vein (depthâ =â 5Â mm) of the mid-arm is cannulated as the blood-returning site under real-time ultrasound guidance. Normally, this vein is not punctured because it is usually invisible, impalpable, and sandwiched between the median nerve and brachial artery. Without dynamic probe scanning, precise and safe cannulation of this vein is difficult. (MP4 13095 kb)