<qa>  What is the minimum effective concentration of local anesthetic required for surgical anesthesia?The aim of this study is to determine the minimum effective concentration of local anesthetic ropivacaine 40mL required to produce an effective double-injection USG-SCB for surgical anesthesia in 90 of patients MEC90 in young group 18-40 years and in middle aged group 40-65 years of patients scheduled for elective surgery of one upper limb distal to the shoulder. 