| Abstract | Since clonidine has a negative chronotropic effect and inhibits catecholamine release, it may blunt sympathetic-mediated heart rate acceleration secondary to vasodilation, thereby enhancing the hypotensive effect of vasodilators. In this study we examined whether preanesthetic clonidine medication would alter the hypotensive effect of nicardipine in surgical patients during general anesthesia. After approval by the local ethical committee and informed consent, 60 surgical patients, ASA I, 24-67 yr, were selected for this study. The patients received oral clonidine approximately 5 μg/kg (clonidine-5 group, n=20) or 2.5 μg/kg (clonidine-2.5 group, n=19) 90 min before anesthesia, while the remaining 21 patients received no clonidine (control group). General anesthesia was induced with thiopental approximately 5 mg/kg, and maintained with an end-tidal concentration of isoflurane 0.3-0.9% and nitrous oxide 67% in oxygen after tracheal intubation. After obtaining hemodynamic stability, nicardipine 10 μg/kg was injected IV in 5 seconds. Blood pressure and heart rate were measured at 1-min intervals for 10 min following nicardipine. Data (mean±SD) were analyzed using ANOVA and Bonferroni's multiple-comparison test, with P<0.05 being significant. There were no significant differences with respect to demographic and pre-nicardipine hemodynamic data. The maximum decreases in mean blood pressure following nicardipine did not differ among the three groups (-15±5, -13±5, -13±6 mmHg in the clonidine-5, clonidine-2.5, and control groups, respectively). These results suggest that oral clonidine 2.5 or 5 μg/kg medication did not enhance the hypotensive effect of nicardipine in normotensive patients during isoflurane anesthesia. |
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