The Tetraphasic Action of Lidocaine on CNS Electrical Activity and Behavior in Cats

Abstract

Effects of i.v. administered lidocaine [local anesthetic] on CNS electrical activities were studied in cats with surface and depth electrodes implanted chronically in the brain. Lidocaine was administered using a constant rate infusion pump. The changes induced in CNS electrical activities were correlated with the behavioral changes in the unrestrained freely moving state. During infusion of lidocaine at the rate of 1 Mg.cntdot.kg-1.cntdot.min-1, a sequence of changes was observed: the initial stage was represented by diffuse EEG slowing and a decrease of reticular neuronal firing, associated with behavioral depression; the 2nd stage by low-voltage fast-wave EEG and increase of reticular neuronal firing, associated with agitation and/or catatonic behavior; the 3rd stage by reappearance of slow-wave EEG and decrease of reticular neuronal firing, associated with a behavioral depression; and the 4th stage by an epileptiform EEG and increase of reticular neuronal firing associated with generalized tonic or tonic/clonic convulsions. Higher rates of infusion, such as 4, 8 and 15 mg.cntdot.kg-1.cntdot.min-1, diminished the manifestation of the signs of both electrographic and behavioral depression, leaving the signs of excitation unaffected or somewhat enhanced. Recording the surface EEG is evidently not valuable diagnostically in detecting the onset of local anesthetic intoxication, in that the preconvulsive CNS state can be represented by either a high-voltage slow-wave or low-voltage fast-wave pattern in the surface EEG.