THE EFFECT OF INTRAVENOUSLY ADMINISTERED DEXMEDETOMIDINE ON PERIOPERATIVE HEMODYNAMICS AND ISOFLURANE REQUIREMENTS IN PATIENTS UNDERGOING ABDOMINAL HYSTERECTOMY

The effects of two doses of dexmedetomidine (0.3 or 0.6-mu-g.kg-1), fentanyl 2.0-mu-g.kg-1, or saline as a single intravenous bolus administered 10 min prior to the induction of anesthesia were assessed in double-blind, randomized study in 96 women undergoing abdominal hysterectomy. In each patient, anesthesia was induced with thiopental 4.0 mg.kg-1, and after the effect of succinylcholine had dissipated, isoflurane 0.3% end-tidal concentration in 70% nitrous oxide was begun to maintain anesthesia. The isoflurane concentration was adjusted to maintain blood pressure and heart rate within 20% of preoperative values, and fentanyl was given if the end-tidal isoflurane concentration exceeded 1.5%. In all groups, blood pressure and heart rate increased after tracheal intubation. However, the increase in blood pressure and heart rate was significantly less in the higher dexmedetomidine (0.6-mu-g.kg-1) group than in the saline group (P < 0.01). Also, the postintubation increase in heart rate was significantly less (P < 0.05) in the dexmedetomidine 0.6-mu-g.kg-1 group (increase of 18 +/- 3 beats per min) compared to the fentanyl group (increase of 26 +/- 3 beats per min). In patients receiving dexmedetomidine 0.3-mu-g.kg-1, the increase in blood pressure or heart rate did not differ from that of the saline group. The mean end-tidal isoflurane concentration was significantly less in the women receiving the higher dose of dexmedetomidine (0.35%) than in those receiving saline (0.47%) or fentanyl (0.48%), although the reduction was not clinically important. Thus, a single intravenous bolus dose of dexmedetomidine 0.6-mu.kg-1, given before the induction of anesthesia, reduced the increase in heart rate in response to tracheal intubation and diminished isoflurane requirements during abdominal hysterectomy, when compared to that required by patients receiving fentanyl 2.0 mg.kg-1. The clinical importance of these effects is unclear and must await studies in patients having more significant cardiovascular disease.