Dose-Finding Study: MEV90 for Local Anesthetic in Interscalene Block for Supraclavicular Nerves Block

This study aims to determine the minimum effective volume (MEV90) of local anesthetic required to achieve sensory block of the supraclavicular nerves when performing a single-shot ultrasound-guided interscalene brachial plexus block (ISB). These nerves provide sensation to the skin over the clavicle and shoulder and are often involved in surgeries such as shoulder arthroscopy and clavicle repair.

Inclusion Criteria: * Age ≥ 18 years * ASA physical status I to III * Body Mass Index (BMI) between 18 and 35 kg/m² * Weight ≥ 50 kg * Scheduled for shoulder arthroscopy requiring an interscalene brachial plexus block for analgesia * Able to provide informed consent Exclusion Criteria: * Inability to provide informed consent * Coagulopathy (platelet count ≤100,000; INR ≥1.4) * Significant pulmonary disease (restrictive or obstructive) * Renal insufficiency (creatinine ≥1.2 mg/dL) * Hepatic insufficiency (transaminases ≥100 U/L) * Allergy to local anesthetics * Pregnancy * Pre-existing neuropathy * Previous surgery in ipsilateral cervical or supraclavicular region * Contralateral hemidiaphragmatic paralysis or vocal cord paralysis