The biphasic pattern of the convulsive property of enflurane in cats.

The nature of the epileptoid state produced by enflurane was examined in the concentration range 2-5% in cats. A biphasic pattern in the convulsant property was revealed. The ease of induction of seizure by repetitive peripheral stimulation, the duration of seizures, and the activation of reticular neuronal firing during seizure activity showed peak values between 3 and 4%, whereas the values were significantly lower both above and below this range. The amplitudes of the somato-sensory evoked potential also showed a biphasic pattern which correlated well with the severity of the epileptoid state as judged by the aforementioned indices. These findings, when compared with evidence on the actions of other convulsant drugs, and with the known depressant actions of enflurane, suggest a combination of depressant and convulsant properties, the balance of which varies depending on the depth of anaesthesia.