DEXMEDETOMIDINE PREMEDICATION ATTENUATES KETAMINE-INDUCED CARDIOSTIMULATORY EFFECTS AND POSTANESTHETIC DELIRIUM

Background: Dexmedetomidine is a new potent and highly selective alpha (2)-adrenoceptor agonist with sedative-hypnotic and anesthetic sparing properties. Because of its sympathoinhibitory activity, it may prove useful in balancing the cardiostimulatory effects and attenuating the adverse central nervous system effects of ketamine. Methods: A double- blind, randomized and comparative parallel-group study design was empl oyed in 40 volunteers with ASA physical status 1 who were scheduled fo r elective superficial surgery under ketamine anesthesia. Dexmedetomid ine (2.5 mu g/kg, n = 20) or midazolam (0.07 mg/kg, n = 20) was admini stered intramuscularly 45 min before induction of anesthesia. Anesthes ia was induced with 2 mg/kg ketamine intravenously, and muscle relaxat ion was achieved with vecuronium. After tracheal intubation, anesthesi a was maintained with nitrous oxide/oxygen (2:1) and additional 1 mg/k g intravenous ketamine boluses according to clinical and cardiovascula r criteria. Hypotension and bradycardia were treated by increasing the intravenous infusion rate of crystalloids and intravenous atropine, r espectively. Sedative and anxiolytic properties, intra- and postoperat ive drug requirements, psychomotor and cognitive impairments, and card iovascular effects were compared between the two groups. Results: Dexm edetomidine and midazolam proved to have equal sedative and anxiolytic effects after intramuscular administration, but dexmedetomidine induc ed significantly less preoperative psychomotor impairment and less ant erograde amnesia than did midazolam. Compared to midazolam, dexmedetom idine decreased the need for intraoperative ketamine and was more effe ctive in reducing ketamine-induced adverse central nervous system effe cts. Dexmedetomidine also was superior to midazolam in attenuating the hemodynamic responses to intubation and the cardiostimulatory effects of ketamine in general, but it increased the incidence of intra- and postoperative bradycardia. Conclusions: These results suggest that pre medication with 2.5 mu g/kg dexmedetomidine is effective in attenuatin g the cardiostimulatory and postanesthetic delirium effects of ketamin e. However, because of its propensity to cause bradycardia, routine us e of an anticholinergic drug should be considered.