Resistance of the auditory brain stem response to high barbiturate levels.

In the comatose patient the auditory brain stem response may be one of the few indices of CNS function available. Because barbiturates may be administered to control intracranial pressure and its sequelae, demonstration of the effect of barbiturates on the brain stem response is desirable. In cats preloaded with 63 mg/kg of pentobarbital, intravenous injection of an additional 60 mg/kg reduced, but did not abolish, the later waves of the response. One cat that survived a cumulative dose of 183 mg/kg continued to show a well-defined brain stem response. Even doses of barbiturate nearly incompatible with survival do not abolish this response.