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study drug infusion, the dexmedetomidine groups had significantly less tachycardia than the placebo group (P = 0.006 placebo vs. low-dose, P = 0.004 placebo vs. medium-dose, P = 0.004 placebo vs. high-dose; This difference was not maintained after discontinuation of dexmedetomidine, after which the amount of tachycardia increased. No trends could be detected in the amount of hypertension or hypotension in the dexmedetomidine groups versus placebo group . The amount of time (minutes/monitored hours) heart rate exceeded predetermined hemodynamic limits (> 20%, > 100 beats/min, < 40 beats/min) intraoperatively (intraop), postoperatively during the study drug infusion (Rx on), and for the first 12 h after the study drug infusion (Rx off) for each group. Data are presented as the mean + SD. *Significantly different (P < 0.05) from placebo. The amount of time (minutes/monitored hours) systolic blood pressure exceeded predetermined hemodynamic limits (> 20%, > 160 mmHg, < 20%, < 90 mmHg) intraoperatively (intraop), postoperatively during the study drug infusion (Rx on), and for the first 12 h after the study drug infusion (Rx off) for each group. Data are presented as the mean plus/minus SD. *Significantly different (P < 0.05) from placebo. There were no significant changes in blood pressure or heart rate during the first 12 h after dexmedetomidine infusion SpO2during dexmedetomidine infusion did not differ significantly from values in the placebo group. None of the patients had SpO2less than 85%. Intra- and postoperatively, the SpOsub 2 was less than 90% < 0.05% of the time in all groups. Intraoperatively, most patients received phenylephrine to maintain systolic blood pressure within predetermined limits: 4 of 6 in the placebo group; five of six in the low-dose group, six of six in the medium-dose group, and six of six in the high-dose group Anticholinergic drugs were required to treat bradycardia intraoperatively in 44% of the patients receiving dexmedetomidine and none of the patients in the placebo group The total amounts of vasoactive medications used for each group did not differ. Intraoperative intravenous fluid and blood-product requirements, urinary output, and blood loss also were similar among the four study groups. Postoperatively, during the study drug infusion, vasoactive drug requirements were minimal. Most interventions occurred in the placebo and low-dose groups, which required esmolol to control heart rate The amount of intravenous fluids and urinary output for each group did not differ postoperatively. . Number of Patients Receiving Intraoperative Vasoactive Medications and Total Dose for Each GroupHolter ECG Monitoring Fourteen of the 24 patients (58%; three subjects in the placebo group, four in the low-dose group, four in the medium-dose group, and three in the high-dose group) had a total of 87 ischemic episodes Three episodes (3%) occurred before study drug infusion, two intraoperatively (2%), 29 postoperatively during the study drug infusion (33%), and 53 during the 48 h after the study drug infusion (61%). Of all ischemic episodes, only 8% occurred in the medium-dose group and 9% in the high-dose group, compared to 29% in the placebo group. Of the two intraoperative ischemic episodes, one occurred during induction of anesthesia (in the high-dose group), and one during emergence from anesthesia (in the medium-dose group). Both were associated with significant increases in heart rate. Neither of these patients had postoperative ischemic episodes.. Number of Ischemic Episodes and Ischemic Burden (min/h) from Holter ECG Analysis during Each Perioperative Period Postoperatively, the amount of myocardial ischemia was higher than preoperatively or intraoperatively for all groups Of the 87 postoperative ischemic episodes, 82 were associated with heart rates greater than 90 beats/min at some point during the episode. All ischemic episodes were associated with heart rates greater than 70 beats/min. Transesophageal Echocardiography Eight of 24 patients (33%) developed echocardiographic evidence of ischemia during the intraoperative period (two in the placebo, three in the low-dose, one in the
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