The aim of this study is to determine the minimum effective volume of local anesthetic (50:50 mixture of 0.5% levobupivacaine and 2% lidocaine) required to produce an effective US-SCB for surgical anesthesia in 50% of patients and to calculate the effective volume required to produce an effective US-SCB in 95% of the patients (MEAV95) in elderly group (>65 years) and in middle aged group (<45years) of patients.