Paraneural Sheath & Fascial Compartments Surround Brachial Plexus at Supraclavicular Fossa During Selective Trunk Block

High definition ultrasound images that were acquired during USG SeTB are routinely stored in the hard disk of ultrasound machine in DICOM (Digital Imaging and Communications in Medicine) format will be used for this review. The images of principal investigator's previous research studies with Clinical trial registration: NCT04752410 and NCT04773405 will also be retrieved. The ultrasound imaging was performed before (scout scan), during and immediately after the USG SeTB. As is the principal investigator's standard practice, all ultrasound scan was performed in a sequential manner (SUIT: Sequential Ultrasound Imaging Technique) with the orientation marker of the transducer directed laterally so as to obtain a transverse oblique view of the brachial plexus block at the supraclavicular fossa. Approximate 50 cases who had undergone USG SeTB for surgical anesthesia during upper extremity surgery since January 1 2020 to June 30, 2021 will be evaluated by two anesthesiologists.