Neurophysiological effects of etomidate, a new short-acting hypnotic

The neurophysiological effects of 0.3 mg/kg etomidate injected i.v. within 30 sec were investigated in 22 healthy volunteers, 7 of whom were premedicated with Thalamonal and fentanyl. About 30 sec after injection, a short period of delta activity (deep sleep) occurred in the EEG, successively normalizing within the next 6-8 min. EEG arousal reactions to various stimuli were blocked for several minutes. In the premedicated group neither motor hyperactivity nor monosynaptic reflex alterations were observed. In contrast, 9 out of 5 non-premedicated subjects exhibited various kinds of motor hyperactivity, consisting most often of asynchronous clonic bursts of activity in the EMG. Clonus was not related to EEG events, and could persist beyond behavioural and EEG recovery. In 12 subjects, the monosynaptic H reflex was enhanced up to 6 X of control. The plantar reflex was reinforced to a generalized withdrawal reaction, sometimes a positive Babinski sign was observed. It is assumed that clonus is generated in spinal circuits, whereas supraspinal structures may contribute to the more complex forms of motor hyperactivity.