In double-injection technique using in plane method and lateral to medial direction half the volume of local anesthetic(15 ml bupivacaine) is injected at intersection of first rib and subclavian artery and another half(15 ml bupivacaine) is injected supero- lateral to subclavian artery to assure spread of the local anesthetic solution in all planes containing brachial plexus. the performance time will be recorded.