Electroencephalographic study of the short-acting hypnotics etomidate and methohexital in dogs

Beagles, implanted with cortical and subcortical electrodes, were given etomidate i.v. (1 mg/kg) over a period of 10 sec. The effects on the EEG were compared with those obtained with 7 mg/kg of methohexital. Both compounds induced hypnosis for a duration of approximately 8 min. The EEGs showed a remarkable similarity. Visual inspection of the records as well as power spectrum analysis revealed a sustained θ-activity with underlying fast activity. The configuration of the waves was rather sharp. The power obtained after etomidate was, however, 2 to 3 times that obtained after methohexital. When the animals awoke from etomidate-induced hypnosis slow waves appeared and were followed by α-activity, whereas after methohexital-hypnosis β-activity predominated. Etomidate slightly increased heart rate, but respiratory depression was not observed. Methohexital caused pronounced tachycardia and apnoea. In 3 out of 6 dogs methohexital caused myclonus of the hind legs upon awakening from anaesthesia. Etomidate induced myoclonus in one dog during hypnosis.