Assessment of ultrasound-guided supraclavicular brachial plexus blocks with different volumes in upper extremity surgery and their effect on opti̇c nerve sheath diameter

Supraclavicular brachial plexus block (SCBPB) is widely used in upper-extremity surgery due to its rapid and reliable anesthetic effect. However, the physiological impact of different local anesthetic (LA) volumes on both block efficacy and optic nerve sheath diameter (ONSD), which is associated with intracranial pressure (ICP), has not been fully clarified. This study aimed to compare the effects of different SCBPB volumes on ONSD changes and block performance under ultrasound guidance. A total of 64 patients aged 18-50 years with ASA physical status I-II who were scheduled for elective upper-extremity surgery were included. Patients were randomized into four groups receiving 15 mL, 20 mL, 25 mL, or 30 mL LA. ONSD was measured bilaterally before the block and at the 20th and 60th minutes and was normalized to eye transverse diameter (ETD). Sensory-motor block onset and duration, perfusion index (PI), time to first analgesic requirement, pain scores, and the need for supplemental LA were also recorded. When the volume groups were compared, both ONSDint/ETD and ONSDext/ETD showed significant differences at the 20th and 60th minutes, with more pronounced increases in the 25 mL and 30 mL groups (p<0.05). Sensory and motor block onset accelerated as the volume increased, and block durations were longer in the 25 mL and 30 mL groups (p<0.001). Time to first analgesic requirement was significantly longer in the 25 mL and 30 mL groups (p<0.001). PI increased in a volume-dependent manner, with faster and more marked rises in higher volumes. No significant differences were found among the groups regarding supplemental LA, tourniquet intolerance, or early postoperative pain scores, and no complications occurred. In conclusion, 20 mL LA provided a more balanced safety profile by limiting the increase in the ONSD/ETD ratio while offering block efficacy comparable to 25-30 mL in ultrasound-guided SCBPB. The 15 mL volume resulted in shorter block duration and earlier analgesic requirement, reducing clinical effectiveness. It was considered that determining the volume to be used in SCBPB with a personalized volume approach may be a safe strategy in patients with a risk of increased ICP or in fragile patients with unpredictable autonomic responses. Keywords: supraclavicular brachial plexus block, optic nerve sheath diameter, globe transverse diameter, local anesthetic volume, ultrasonography