Effects of oral and subarachnoid clonidine on spinal anesthesia with bupivacaine.

This study was designed to determine whether clonidine has analgesic properties, decreases the minimum alveolar concentration of inhalational anesthetics, or affects the quality and the duration of spinal anesthesia with bupivacaine. The comparative effects of oral and subarachnoid clonidine on spinal anesthesia with bupivacaine were studied in 36 patients scheduled for orthopedic surgery. Patients were allocated randomly into four groups to receive either oral diazepam (10 mg in Groups I and II) or oral clonidine (150 micrograms and 300 micrograms in Groups III and IV, respectively), as premedication. Spinal anesthesia was performed with 15 mg hyperbaric bupivacaine 0.5% plus either 1 ml isotonic saline in Groups I, III, and IV, or 150 micrograms clonidine in Group II. Subarachnoid but not oral clonidine significantly prolonged the duration of sensory block (time for regression to L2 was 157 +/- 21 minutes in Group I and 267 +/- 75 minutes in Group II) and the duration of motor block (duration of Grade 3 motor block--Bromage scale--was 103 +/- 20 minutes in Group I and 175 +/- 68 minutes in Group II). Only the subarachnoid administration of clonidine achieves adequate concentrations to significantly increase the duration of spinal anesthesia.