Association Between Local Anesthetic Volume–Dose Combinations and Optic Nerve Sheath Diameter as an Indirect Marker of Intracranial Pressure During Ultrasound-Guided Supraclavicular Brachial Plexus Block: A Randomized Trial

Background and Objectives: This prospective, randomized study aimed to evaluate the effects of different local anesthetic (LA) volume–dose combinations administered during supraclavicular brachial plexus block (SCBPB), a widely used technique in upper extremity surgery. These effects were assessed by analyzing changes in the ratios of optic nerve sheath diameter (ONSD) to eyeball transverse diameter (ETD), obtained by ultrasound (US) and considered indirect measures of intracranial pressure (ICP). Materials and Methods: Sixty four ASA I–II patients aged 18–50 years undergoing upper extremity surgery were randomized into four groups receiving 15 mL (Group A), 20 mL (Group B), 25 mL (Group C), or 30 mL (Group D) of LA (equal volumes of 0.5% bupivacaine and 2% prilocaine). ONSD/ETD ratios were measured bilaterally at baseline, 20, and 60 min. Perfusion index (PI), end-tidal carbon dioxide (EtCO2), block onset times and block duration were also assessed. Results: Groups C and D showed significant bilateral increases in both ONSDint/ETD and ONSDext/ETD ratios at 20 and 60 min compared with baseline (p < 0.05). Group B demonstrated a significant increase only in the ONSDext/ETD ratio on the block side, whereas Group A showed no significant change. PI increased earlier and more markedly with increasing LA volume–dose. No significant intergroup differences were observed in EtCO2. In pairwise comparisons, sensory block onset was significantly longer in Group A than in Groups B, C, and D (p < 0.001). Motor block onset was significantly longer in Group A than in Groups C and D, and in Group B than in Group D (p < 0.001). Analgesia duration was significantly shorter in Group A than in Groups B, C, and D, and in Group B than in Groups C and D (p < 0.001). Conclusions: Increasing the LA volume–dose in US-guided SCBPB accelerates sensory and motor block onset and significantly prolongs block duration. A volume-dependent increase in ONSD/ETD ratios was observed on both the blocked and contralateral sides. PI showed an early and marked increase, particularly in high-volume–dose administrations, reflecting block success. Non-invasive EtCO2 monitoring did not detect significant changes.