Catheter-related bladder discomfort (CRBD) is not uncommon in male patients under general anesthesia, and it may cause patient agitation and exacerbated postoperative pain. In this study, the investigators will enroll male patients undergoing elective prostate surgery with urinary catheterization after anesthetic induction, and compare the efficacy of pudendal nerve block (PNB) and intravenous tramadol in prevention of CRBD.

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:

The PNB group: patients will be given bilateral pudendal nerve block with 30ml of 0.33% ropivacaine (15ml for each side) after the completion of surgery before extubation.

The TRAM group: patients will be given tramadol of 1.5mg/kg after the completion of surgery before extubation.

All patients will be evaluated by a research nurse who were blinded to the group assignments for outcomes at 0, 1, 2, 4, and 6h after patients' arrival in PACU, and after extraction of urinary catheter.

The primary outcome is the incidence of postoperative CRBD. The secondary outcomes include the severity of postoperative CRBD, postoperative tramadol requirement and number of patients with requiring postoperative tramadol, numeric rating scale (NRS) for postoperative pain, postoperative sufentanil requirement and number of patients with requiring postoperative sufentanil, postoperative side effects, and acceptance of indwelling urinary catheter after extraction of the catheter.

All primary and secondary endpoints will be analyzed on an intent-to-treat basis. Analyses are performed with the use of SPSS 18.0 software. The Student-t test is used to analyze demographic data in the two groups. The incidence of CRBD and side effects between groups are analyzed by Chi-square test, whereas the severity of CRBD (mild, moderate, and severe) is analyzed by Fisher's exact test. NRS scale is analyzed by the Mann-Whitney test. Postoperative tramadol and sufentanil requirement is analyzed by Z test, and the number of patients requiring tramadol for CRBD rescue treatment and sufentanil for postoperative pain will be analyzed with Fisher's exact test. A P value<0.05 is considered significant.

Inclusion Criteria:

• Patients aged 18years to 75years.
• American Society of Anesthesiologists (ASA) physical status I, II, or Ⅲ.
• Undergoing elective prostate surgery at lithotomy position with urinary catheterization after anesthetic induction under general anesthesia.
• Glasgow Coma Scale (GCS) score of 15. Ability to communicate.

Exclusion Criteria:

• History of bladder dysfunction, such as over active bladder (OAB, urinary frequency: more than three times in the night or more than eight times in 24 h).
• History of bladder outflow obstruction.
• Neurogenic bladder.
• Impaired renal function.
• Coagulopathy.
• Known allergies to any anesthetic agent.
• Family history of malignant hyperthermia.
• Impairment of communication or cognition.
• Psychopathy.
• Active participation in another trial where the primary endpoint follow-up is ongoing.
• Unwillingness or inability to comply with protocol procedures.

It is undecided whether to share IPD