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no dose-dependent decrease in blood pressure during the study drug infusion. It is possible that the postoperative stress response was sufficient to overcome the blood pressure-lowering effect of dexmedetomidine or that there is tachyphylaxis to the effects of dexmedetomidine. Patients who are dependent on a high level of sympathetic activity or have a reduced myocardial function might not be able to tolerate the decrease in sympathetic tone by dexmedetomidine. Whether their sympathetic tone is decreased to the same extent by dexmedetomidine as in patients with normal sympathetic tone is not known. The current study did not have patients in this category, and future studies need to verify the safety of dexmedetomidine in these patients. High dexmedetomidine plasma levels may increase blood pressure due to the effect of dexmedetomidine on peripheral alpha2receptors. Consistent with two previous reports, we observed an initial increase in the systolic blood pressure with our high-dose group (0.45 ng/ml) within 2–3 min of the start of infusion. Because the increase in blood pressure is related to high peak plasma dexmedetomidine concentrations, it may be circumvented by slower administration of dexmedetomidine. A high incidence of bradycardia and use of anticholinergic drugs have been reported in several studies using intravenous or intramuscular dexmedetomidine in healthy surgical patients. We administered dexmedetomidine for 1 h before induction of anesthesia to assess the effect of dexmedetomidine on myocardial conduction in unanesthetized, unstimulated patients. Although dexmedetomidine gradually decreased heart rate, there were no sudden episodes of bradycardia, new conduction blocks, or new dysrhythmias. Intraoperatively, 8 of 18 patients receiving dexmedetomidine required anticholinergic drugs for bradycardia (HR < 40 beats/min). Up to a 33% incidence of postoperative bradycardia has been reported with the use of dexmedetomidine in healthy surgical patients. The low incidence of postoperative bradycardia (1 of 24 patients) in our study population could be due, in part, to differences in the sympathetic and parasympathetic tones or vagal responsiveness between our patients with preexisting vascular disease and young, healthy, surgical patients, or to an effect of postoperative stress sufficient to overcome some of the heart rate-lowering effect of dexmedetomidine. The results of the current study indicate that, in vascular surgery patients, dexmedetomidine blunts the increase in rate-pressure product in response to emergence from anesthesia. However, the present study cannot demonstrate conclusively that dexmedetomidine attenuates the hemodynamic changes in response to emergence, because the variables (HR, SBP) used to calculate the rate-pressure product were not significantly affected by dexmedetomidine. Intraoperatively, the patients receiving dexmedetomidine required frequent use of vasopressors and anticholinergic medications to maintain systolic blood pressure and heart rate within the predetermined limits. There were no adverse effects from the frequent intraoperative use of phenylephrine and no further need for blood pressure support postoperatively, suggesting that any decrease in postoperative sympathetic activity with dexmedetomidine was not significant enough to cause postoperative hypotension. Recent studies of other alpha2agonists suggest that these agents may be effective therapies for postoperative myocardial ischemiaOur study was limited by a small number of patients in which only a few patients in each group had myocardial ischemia. Our small sample size limited the statistical power to discriminate among the groups. Further studies in a larger number of patients will be needed to evaluate whether alpha2agonists have antiishemic effects, as has been suggested by preliminary studies using clonidine. Aho et al. reported that a continuous intraoperative dexmedetomidine infusion can decrease the requirements for isoflurane by up to 90% in healthy patients. Our intraoperative use of alfentanil and nitrous oxide provided sufficient anesthesia for our
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