For the continuous block: A 4 gauge 18 inch tuohy needle ( B -Braun) will be introduced towards the posterior cord as above. When the needle tip and the pattern of spread is confirmed using D5% solution, a 21 gauge catheter will be introduced 2 cm beyond the needle tip under ultrasound visualization. The needle will be withdrawn over the catheter. Injection of a total of 20 ml of ropivacaine 0.5% ( in divided 5 ml boluses with intermittent aspiration) will take place through the catheter while observing the spread of local anesthetic under ultrasound. The catheter hub will be affixed to the upper lateral chest with sterile occlusive dressings and an anchoring device.