The purpose of this study was to determine if clonidine reduces myocardial ischemia or alters anesthetic requirement and perioperative hemodynamic parameters during coronary artery bypass grafting (CABG) surgery. Forty-three patients were randomized in a prospective, double-blind fashion to receive either clonidine (5 micrograms/kg) or placebo. Anesthetic induction and maintenance was accomplished with intravenous sufentanil-midazolam (S-M) in a 1:20 ratio; up to 1.0% enflurane was added during surgery when repeated boluses of S-M failed to maintain the blood pressure within 20% of preinduction values. Continuous ST segment analysis of leads II and V5 was performed throughout surgery with maximal ST segment deflection from baseline recorded every 5 minutes. Catecholamine levels were measured intermittently throughout the perioperative period and myocardial lactate use or excretion was determined just prior to cardiopulmonary bypass (CPB) and at 1, 5, 10, 30, and 60 minutes after release of the aortic cross-clamp. Patients who received clonidine required significantly less sufentanil for their surgical procedure (11.82 +/- 0.66 micrograms/kg v 14.55 +/- 0.90 micrograms/kg, P < 0.05) and also needed less enflurane for blood pressure control, particularly during CPB (P < 0.05). Baseline hemodynamic parameters were similar for both groups prior to induction. In the period between anesthetic induction and the initiation of CPB, patients treated with clonidine had a significantly slower heart rate (HR) (P < 0.01), a lower cardiac output (CO) (P < 0.05), and transiently higher systemic vascular resistance (SVR) (P < 0.05) than placebo-treated patients. Immediately after CPB, patients receiving clonidine continued to have a significantly lower CO (P < 0.01) and a higher SVR (P < 0.01) than placebo-treated patients. Clonidine treatment significantly increased the percentage of patients who required pacing after CPB (P < 0.05). In the intensive care unit, clonidine-treated patients displayed a persistently increased requirement for pacing (P < 0.01), decreased systolic blood pressures, and reduced sodium nitroprusside requirements relative to patients treated with placebo. Epinephrine and norepinephrine levels were lower in clonidine-treated patients throughout the perioperative procedure with significant differences noted immediately following sternotomy and release of the aortic cross-clamp (P < 0.05). Critical ST segment depression was significantly less in clonidine-treated patients for the period from sternotomy until application of the aortic cross-clamp (P < 0.01). Following CPB, absolute deviation of ST segments from isoelectric baseline was significantly less in the clonidine-treated group (P < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)