Recently many studies reported that intraoperative dexmedetomidine administration undergoing spinal anesthesia give a satisfactory sedation in elderly patients and cause less respiratory depressions compared other sedatives(e.g. benzodiazepine) But the optimal dose of dexmedetomidine for sedative effect in elderly patients undergoing spinal anesthesia was not got general consensus.

The investigators hypothesized that the dose requirements would be lower than in elderly patients than young patients. Furthermore, intrathecal small dose opioids enhance the analgesia provided by bupivacaine due to synergistic effects and it would reduce the dose of dexmedetomidine.

The purpose of this study was to determine the dose of dexmedetomidine to provide satisfactory sedation undergoing spinal anesthesia with or without additive small dose intrathecal opioids.

Elderly patients(65~85 years old) undergoing TURP or TURB were enrolled in this single-blinded study. Forty patients were randomly assigned to receive intrathecal hyperbaric bupivacaine 6mg coadministered with 20mcg fentanyl or placebo normal saline 0.4cc. After the induction (bilateral T10 sensory level to pinprick within 5 mins of intrathecal drug administration), continuous intravenous dexmedetomidine was started in dose of 0.8, 0.6, 0.5, 0.4, 0.3, or 0.2mcg. Successful sedation was defined as OASS score 3 or 4 within 20 minutes of dexmedetomidine infusion. The dose of dexmedetomidine was selected for each patient according to an up and down method. Intraoperative arterial pressure, heart rate, and bispectral index was compared. Postoperative pain score, the time for the regression of sensory and motor was recorded for further analysis.

Inclusion Criteria:

• Elderly patients aged 65~85 years olds undergoing TURB or TURP.
• No contraindication of spinal anesthesia.
• ASA class I and II.
• Patients consented to spinal anesthesia were enrolled.

Exclusion Criteria:

• Patients with hypovolemia, coagulation disorders, local infection at the site of operation, history of headache, heart diseases, and history of allergy, chronic alcohol use or abuse, anemia, congenital heart diseases, bundle block, congestive heart failure or arrythmias, and patients who had recently received sedative drugs or were under antidepressant treatment were not included in the study.