Dural Sac Area-Guided Spinal Anesthesia Dosing for TURP

This prospective, randomized controlled study compares two routinely used approaches todetermining the intrathecal bupivacaine dose for spinal anesthesia in patients undergoingtransurethral resection of the prostate (TURP). No new drug, new indication, orexperimental treatment will be introduced. Both dosing approaches are currently used inroutine clinical practice; the study will prospectively and randomly compare theirclinical effects.Participants will be randomly assigned to either a dural sac cross‐sectional area(DSCSA)‐guided individualized dosing group or a fixed‐dose control group.Before spinal anesthesia, the anteroposterior diameter of the dural sac will be measuredby ultrasound at the L3‐L4 intervertebral level. DSCSA will be calculated using theformula A = π × (D/2)².In the individualized‐dose group, a DSCSA of 150 mm² will be used as the reference valuecorresponding to 10 mg of intrathecal bupivacaine. The bupivacaine dose will be adjustedproportionally according to the participant's calculated DSCSA and limited to a minimumof 6 mg and a maximum of 12.5 mg. Fentanyl 25 micrograms will be added intrathecally.In the fixed‐dose group, participants will receive 10 mg (2 mL of 0.5%) intrathecalbupivacaine together with fentanyl 25 micrograms.Spinal anesthesia will be performed at the L3‐L4 intervertebral space using a 27‐gaugeQuincke needle. Standard intraoperative monitoring will be performed according to thestudy protocol. Sensory and motor block characteristics and hemodynamic variables will berecorded prospectively for comparison between the two dosing strategies.