The brachial plexus will be visualized using a high-frequency linear ultrasound transducer in the supraclavicular fossa. After skin disinfection and infiltrating with 1% lidocaine, nerve stimulation needle will be inserted using in-line technique,and advanced among the divisions of brachial plexus with electric impulses (2 Hz, 0.3mA, 0.1 ms) of nerve stimulator. If visible contraction of the innervated muscle is elicited, the needle will be withdrawn slowly until the corresponding muscle contraction disappears to avoid intrafascicular puncture. The local anesthetic will be injected at three locations: adjacent to the superficial divisions of the plexus, adjacent to the middle divisions and inferior divisions. The proportion of the volume injected in each area is at the discretion of the expert operator according to the spread of local anesthetic.