Hemodynamic effects of oral clonidine premedication in lumbar epidural anesthesia

Clonidine, an α₂-adrenergic agonist, has a potent sympatholytic effect and augments the pressor effect of ephedrine during general anesthesia. We evaluated whether oral clonidine premedication would alter the hemodynamic changes and enhance the pressor response to intravenous ephedrine during epidural anesthesia in 35 adult patients. They were randomly administered either premedication with clonidine approximately 5 μg·kg^-1 po (n=17) or no clonidine medication (n=18). After establishment of epidural anesthesia, the hemodynamic response to ephedrine iv was measured in the awake state at 1-min intervals for 10 min. Then, the same hemodynamic measurement was repeated in the asleep state induced with midazolam iv. There were no differences in blood pressure (BP) and heart rate values between groups during the onset of epidural anesthesia, except that BP before epidural anesthesia was lower in the clonidine group than the control group (P<0.05). The magnitude and duration of pressor responses to ephedrine were comparable between groups in awake and asleep states. In conclusion oral clonidine premedication 5 μg·kg^-1 alters neither the hemodynamic changes nor the pressor response to intravenous ephedrine during epidural anesthesia.