INTRAMUSCULAR DEXMEDETOMIDINE AS PREMEDICATION FOR GENERAL-ANESTHESIA- A COMPARATIVE MULTICENTER STUDY

Background: Dexmedetomidine is a new potent and selective alpha2-agoni st that might prove useful as a preanesthetic agent. Methods. A random ized, double-blind study design was used in 192 ASA physical status 1 and 2 patients scheduled for elective abdominal hysterectomy, cholecys tectomy, or intraocular surgery under general anesthesia. Intramuscula r injection of 2.5 mug/kg dexmedetomidine administered 60 min before a nd intravenous saline placebo 2 min before induction of anesthesia (DE XPLA group, n = 64) was compared with a combination of 0.08 mg/kg intr amuscular midazolam 60 min and 1.5 gg/kg intravenous fentanyl 2 min be fore induction (MIDFENT group, n = 64), or a combination of intramuscu lar dexmedetomidine and intravenous fentanyl (DEXFENT group, n = 64). After thiopental induction, anesthesia was maintained with 70% N2O/O2, and fentanyl was administered according to clinical and cardiovascula r criteria. Patients undergoing cholecystectomy received additional en flurane. Results. Dexmedetomidine and midazolam induced comparable pre operative sedation and anxiolysis. The DEXFENT combination blunted the increases in blood pressure and heart rate induced by tracheal intuba tion more efficiently when compared with the DEXPLA and MIDFENT groups , in which approximately 25 mmHg and 15 beats/min greater increases we re observed. The intraoperative fentanyl requirements were greater in MIDFENT patients when compared with both dexmedetomidine groups, in wh ich 56% (DEXFENT group) and 31% (DEXPLA group) less fentanyl, respecti vely, was needed. Intraoperatively, fluids or vasopressors for hypoten sion and glycopyrrolate for bradycardia were administered more often t o patients receiving dexmedetomidine than to those who did not. Postop eratively, there were no differences in oxygen saturation, analgesic, or antiemetic requirements, but dexmedetomidine-induced blood pressure and heart rate reductions were still evident at the end of the 3-h fo llow-up period. Bradycardia as an adverse event was reported more freq uently in dexmedetomidine patients (20% in the DEXPLA and 33% in the D EXFENT groups) than in MIDFENT patients (8%). Conclusions. The results suggest that pretreatment with a single intramuscular injection of 2. 5 mug/kg dexmedetomidine is efficacious, but significantly increases t he incidence of intraoperative hypotension and bradycardia in ASA phys ical status 1 or 2 patients.