group I:Using 0.75% ropivacaine for traditional combined spinal-epidural anesthesia

Determining the minimum local anesthetic dosage of ropivacaine in elderly patients undergoing lower urinary tract surgery in real-time ultrasound-guided combined spinal epidural anesthesia and traditional combined spinal epidural anesthesia

Determining the minimum local anesthetic dosage of ropivacaine in elderly patients undergoing lower urinary tract surgery in real-time ultrasound-guided combined spinal epidural anesthesia and traditional combined spinal epidural anesthesia