Background: Prolongation of spinal anesthesia by oral clonidine premedication has been known. We hypothesized that intravenous clonidine administered after the spinal block may prolong spinal anesthesia.
Methods: To assess the prolongation of spinal anesthesia by intravenous clonidine, we designed a double-blind, placebo-controlled, prospective study. Patients scheduled for orthopedic surgery received 12 mg of 0.5% hyperbaric bupivacaine and were randomly divided into three groups (n = 26 in each group). In the clonidine 10-min group, 3 microg x kg-1 of clonidine was administered for 10 min immediately after the spinal block. In the clonidine 60-min group, 3 microg x kg-1 of clonidine was administered for 10 min, 50 min after the spinal block. The control group received normal saline. Sensory block was evaluated by pinprick and the duration was defined as the time for sensory block to regress to L1 dermatome. Duration of motor block was defined as the time required for the patient to flex his or her knee.
Results: The duration of sensory block was longer in both the clonidine 10-min and clonidine 60-min groups compared with the control group (196 +/- 42 min, 179 +/- 41 min vs. 125 +/- 25 min, P < 0.05). The duration of motor block was longer in the clonidine 10-min group than in the control group (153 +/- 26 min vs. 131 +/- 29 min, P < 0.05). The lowest heart rate and mean blood pressure were not different among groups.
Conclusions: Intravenous clonidine administration within 1 h after the spinal block prolonged bupivacaine spinal anesthesia for approximately 1 h without adverse effects.