[Effects of thiopental on sensory evoked potentials in the cat]

Noninvasive electrophysiological evaluation with sensory evoked potentials would be of clear diagnostic and prognostic value in evaluating comatose patients with stroke or severe head injury. In order to protect the brain from such kinds of insults, barbiturate coma therapy has been employed and its effectiveness has been already established. However, in the barbiturate coma therapy, it is occasionally difficult to distinguish the pharmacological effect of barbiturate from the preexisting brain dysfunction caused by the underlying process of the disease. In adult cats, authors studied changes of sensory evoked potentials following cumulative intravenous administration of thiopental which is used clinically for barbiturate coma therapy. P1 and N1 of cortical SEP showed tendency of gradual decrease in amplitude. However, no significant changes occurred in latency by stepwise increment of thiopental dose. Changes in amplitude of P1 and N1 of cortical SEP preceded to the flattening on electroencephalogram. Around at the level of the concentration where EEG changes began, I-II interpeak latency of BAEP and latency of wave I of short latency SEP started to increase. BAEP and early components of SEP (I.II.III.IV) persisted even in by far the higher level of serum concentration of thiopental than that of clinical use. Furthermore, most of these parameters showed no statistically significant change neither in amplitude nor in latency. These experimental results suggest that sensory evoked potentials will provide us with useful information in the assessment of the brainstem function in patients under thiopental induced deep coma.