Dural Sac Area-Guided Spinal Anesthesia Dosing for TURP

This randomized controlled study will evaluate whether individualizing the dose of spinal anesthesia according to the ultrasound-derived dural sac cross-sectional area (DSCSA) can improve hemodynamic stability in patients undergoing transurethral resection of the prostate (TURP). Participants aged 40 years or older will be randomly assigned to one of two groups. In the individualized-dose group, the anteroposterior diameter of the dural sac will be measured by ultrasound at the L3-L4 level, and DSCSA will be calculated from this measurement. The dose of intrathecal bupivacaine will then be individualized according to the calculated DSCSA. In the control group, participants will receive a fixed dose of intrathecal bupivacaine. Both groups will also receive intrathecal fentanyl. The main outcome is the incidence of intraoperative hypotension. The study will also evaluate the number of hypotensive episodes, minimum mean arterial pressure, vasopressor and atropine requirements, sensory and motor block characteristics, respiratory monitoring parameters, cerebral oxygenation, and adverse events. The study aims to determine whether a DSCSA-guided dosing strategy can reduce excessive spinal block and improve hemodynamic stability while maintaining effective spinal anesthesia.