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.

Study Summary

64 patients undergoing upper extremity surgery were randomized to receive ultrasound-guided supraclavicular brachial plexus block (SCBPB) using 15, 20, 25, or 30 mL of local anaesthetic (LA), consisting of equal volumes of 0.5% bupivacaine and 2% prilocaine. The primary outcome was the change in optic nerve sheath diameter (ONSD), expressed relative to eyeball transverse diameter (ETD), as an indirect marker of intracranial pressure (ICP). Secondary outcomes included perfusion index (PI), end-tidal carbon dioxide (EtCO2), sensory and motor block onset, supplemental LA requirements, and postoperative pain. ONSD was assessed at baseline, 20, and 60 minutes, while postoperative pain was evaluated up to 24 hours. Overall, the results revealed that 25 and 30 mL significantly increased bilateral ONSD/ETD ratios, whereas 15 mL produced no significant changes. Higher volume–dose combinations also accelerated block onset and prolonged analgesia. These findings suggested a trade-off between improved block characteristics and changes in indirect markers of ICP, although clinically significant intracranial hypertension was not established.