Single-shot Versus Slow Infusion Interscalene Block and Its Impact on Diaphragmatic Function in Patients Undergoing Shoulder Surgery.

Interscalene brachial plexus block is a commonly chosen anesthetic technique for shoulder and proximal arm surgery yet it carry several risks including phrenic nerve block. Researchers assumed that slow administration of local anesthetic would reduce incidence of phrenic nerve block

patients will be randomly allocated into one of 2 groups ( single shot group) and slow administration group . single shot will receive a 10 ml bolus of 0.5% bupivacaine the other group will receive 10 ml 0.5 % bupivacaine over 10 minutes (at a rate of 1ml/minute) using syringe pump An experienced operator who will be blinded to method of administration will conducted diaphragmatic excursion of ipsilateral hemidiaphragm using curved probe at baseline and at 10 minutes interval for 30 minutes Complete phrenic will be defined as 75% or more reduction in DE, while partial failure as 25%-50% reduction in DE