DEXMEDETOMIDINE AND HALOTHANE PRODUCE SIMILAR ALTERATIONS IN ELECTROENCEPHALOGRAPHIC AND ELECTROMYOGRAPHIC ACTIVITY IN CATS

Dexmedetomidine, an alpha(2)-adrenergic agonist, produces sedation and reduces volatile anesthetic requirements, This investigation compared the actions of dexmedetomidine and halothane on the processed EEG and on the electromyogram (EMG) which has not been previously described. Chronically instrumented cats were prepared with arterial and venous c annulae, quadriceps EMG electrodes and EEG electrodes in the lateral g eniculate nucleus and over the frontal and occipital cortices, Hemodyn amics, EEG and EMG were recorded in the conscious state and after rand omly administered halothane or intravenous dexmedetomidine (on separat e days). Blink and tail-clamp responses also assessed level of conscio usness. Halothane resulted in unconsciousness and a lack of response t o tail clamping, while dexmedetomidine produced profound sedation, wit h preservation of tail-clamp responses. Both agents similarly decrease d (P < 0.05) the median power frequency from 9.5 +/- 0.9 to 5.7 +/- 0. 4 Hz (2% halothane) and from 9.6 +/- 0.7 to 5.9 +/- 0.8 Hz (20 mu g/kg dexmedetomidine), and 95% power frequency from 23.0 +/- 0.2 to 18.2 /- 0.6 Hz (2% halothane) and from 23.0 +/- 0.2 to 19.1 +/- 0.8 Hz (20 mu g/kg dexmedetomidine). Both agents increased the total spectral pow er and delta band power of the EEG and reduced integrated EMG activity . Halothane and dexmedetomidine produced differing effects on level of consciousness as assessed by response to tail clamping. The results s uggest that conventional processing of EEG and EMG parameters are inad equate to assess anesthetic depth in the presence of alpha(2)-adrenerg ic agonists. (C) 1997 Elsevier Science B.V.