Abstract
Forty-eight healthy patients undergoing elective abdominal surgery were studied to evaluate the effect of clonidine on the MAC (ED50) of isoflurane and perioperative hemodynamic variables. These patients were divided into two groups: the first group consisted of 24 patients with age of 31-55 years, and the second group 24 patients with age of 56-80 years. Patients were premedicated with 4.0-5.5μg/kg clonidine PO 90 minutes before arriving at the operating room. Anesthesia was induced with isoflurane, oxygen and nitrous oxide and maintained with isoflurane and oxygen until the skin incision was made.
ED50 and ED95 were 0.825±0.017% and 0.926% in the younger group and 0.703± 0.018% and 0.816% in the elder group. Anesthetic requirements were reduced by 28.3% for the younger group and by 33.0% for the elder group compared with the previously reported values without clonidine. Reductions of both systolic and diastolic arterial pressure were observed 90 minutes after premedication in the younger group only, while the elder group remained the same. No change in heart rate occured in both groups. Hypotention was common after induction of anesthesia prior to the skin incision in both groups. Severe bradycardia (heart rate<40bpm) during abdominal manipulation occured more frequently in the elder group than in the younger group. We conclude that clonidine reduces isoflurane MAC by approximately 30%, but the high incidence of severe bradycardia may limit the administration of clonidine as premedication for the elderly.
