• Toru Goyagi, Tomohito Minamizono, Makoto Tanaka, and Toshiaki Nishikawa.
• Department of Anesthesiology, Akita University School of Medicine, Akita.
• Masui. 2005 Sep 1;54(9):992-7.

BackgroundPropofol induces suppression of the sympathetic nervous activity, and attenuates the heart rate responses to intravenous atropine. Similarly, clonidine suppresses the heart rate response to intravenous atropine under awake and enflurane-anesthetized patients. The purpose of this study is to evaluate effects of clonidine on the heart rate response to atropine under propofol anesthesia.MethodsThirty-two adults patients were randomly assigned to one of two groups. Clonidine group (n=16) patients received oral clonidine 5 microg x kg(-1) and famotidine 20 mg, and the control group (n=16) patients received oral famotidine alone 90 minutes before anesthesia. After tracheal intubation, anesthesia was maintained with propofol at the effect site concentration of 3 microg x ml(-1) in air and oxygen using the TCI system. All patients received incremental doses of IV atropine 5 microg x kg(-1) over 5 s at 2-min intervals until heart rate increased > 20 beats x min(-1) from baseline values or until atropine 40 microg x kg(-1) was given.ResultsAlthough heart rate response to atropine 5-25 microg kg(-1) was similar between the two groups, heart rate response to atropine 30 microg x kg(-1) in the clonidine group was smaller than that in the control group (P<0.05). When the atropine 40 microg x kg(-1) was administered, heart rate increased > 20 beats x min(-1) in all patients of the control group, but 62.5% of patients in the clonidine group (P< 0.05).ConclusionsOral clonidine premedication attenuates the heart rate responses to IV atropine under propofol anesthesia.

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