Phase 1 Brachial plexus block (BPB) is a widely used regional anesthetic technique for upper limb surgery. The effect of sympathetic block of BPB can leads to vasodilatation and increase blood flow and skin temperature in the ipsilateral upper limb. At the level of the axillary region, the sympathetic nerves innervating the radial and ulnar artery travel with the brachial plexus, but it is unclear which specific nerve: musculocutaneous, radial, ulnar, and median innervates radial or ulnar artery. Radial and ulnar artery and their branches are common donor or recipient vessels in the vascular reconstruction surgery and their hemodynamic changes may affect the blood flow of vascular anastomoses in vascular reconstruction. Sometimes, brachial plexus could be partially blocked intentionally or unintentionally, with the resultant regional hemodynamic changes unclear.