The PNB trial is an investigator-initiated, prospective, randomized controlled trial that will test the superiority of pudendal nerve block with 0.33% ropivacaine to intravenous tramadol 1.5mg/kg for CRBD prevention. A total of 94 patients undergoing elective prostate surgery at lithotomy position with urinary catheterization (16 G Fr Foley catheter) after anesthetic induction under general anesthesia will be enrolled at West China Hospital of Sichuan University. Patients will be divided randomly into two groups: