The present prospective within-subject observational study will evaluate whether unilateral brachial plexus block (BPB) induces measurable lateralized autonomic modulation, assesses using bilateral Nociception Level (NoL) monitoring during standardized intraoperative stimuli under general anesthesia. Regional anesthesia efficacy is traditionally assessed through sensory and motor examination. However, objective physiologic markers reflecting sympathetic modulation remain limited. Forty five adults undergoing upper extremity surgery with BPB and general anesthesia, bilateral NoL monitoring will be performed during local anesthetic injection, endotracheal intubation, and nasogastric tube placement. The primary aim to investigate whether the brachial plexus block induces unilateral modulation of post-operative nervous system activity, assessed by inter-limb differences in NoL values during predefined nociceptive stimuli under general anesthesia. The secondary aim to evaluate the correlation between postoperative metrics, postoperative pain intensity, and analgesic consumption. From a clinical perspective, bilateral autonomic monitoring may offer a novel adjunctive method for intraoperative confirmation of block activity, particularly in sedated or anesthetized patients where traditional sensory testing is not feasible. Furthermore, inter-limb autonomic gradients could represent a future research pathway for objective assessment of regional anesthesia effectiveness beyond subjective pain scores.