Oral Clonidine Premedication Enhances the Pressor Response to Ephedrine During Spinal Anesthesia

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Abstract
Clonidine premedication enhances the pressor effects of ephedrine in awake and anesthetized patients. To test the hypothesis that clonidine augments the pressor response to ephedrine during spinal anesthesia, 48 ASA physical status I or II patients were randomly assigned to either the clonidine group (n = 23), receiving oral clonidine approximately 5 microg/kg 90 min before spinal anesthesia, or the control group (n = 25), receiving no clonidine. Spinal anesthesia was performed at either the L2-3 or the L3-4 interspace using 0.5% hyperbaric tetracaine solution 1.4-3.0 mL. Blood pressure (BP), heart rate, and the upper dermatomal level of analgesia were determined at 1-min intervals with the patient in the supine position after tetracaine injections. When systolic BP decreased to <80% of the prespinal value or <100 mm Hg, IV ephedrine 0.2 mg/kg was administered as a bolus. There were no differences in the duration until the first dose of ephedrine after tetracaine injections, and the upper level of analgesia between groups (control group 8.5+/-3.7 min, T5; clonidine group 7.7+/-2.7 min, T6). Although prespinal and preephedrine BP values were higher in the control group, the magnitude of increases in mean BP after ephedrine was significantly greater in the clonidine group (P < 0.05). We conclude that oral clonidine premedication augments the pressor response to IV ephedrine during spinal anesthesia. The pressor effect of ephedrine is enhanced in patients given oral clonidine premedication during spinal anesthesia.