The influence of intravenous anaesthetics on enflurane-induced central nervous system seizure activity

Abstract

ENFLUIaANE is a halogenated ether which has been recently introduced into clinical anaesthetic practice. Its attractive features include rapid induction and emergence, minimal gastro-intestina] disturbance and limited biotransformation. However, sufficient concern exists about its potential for eliciting excitation of the central nervous system (CNS) that the manufacturer considers a pre-existing seizure disorder a eontraindication to its use. 1 Recent reports indicate that enflurane-induced EEG seizures, sometimes accompanied by convulsive activity, may be seen in patients with no apparent pre-existing CNS disorder3 -5 Identical EEG seizure patterns can be reproduced in healthy animal preparations. ~9 High inspired concentrations of enflurane and/or low carbon dioxide tensions are well established as factors precipitating or augmenting abnormal EEG activity both in man and in laboratory animals.However, little information is available about the influence on enflurane seizure patterns of other anaesthetic agents used concomitantly. Virtue reported the abolition of enflurane-induced myoclonus in dogs with intravenous thiopentone. TM Dobkin and associates noted the absence of motor movements in patients given enflurane in combination with barbiturates and muscle relaxants but, in common with other early clinical evaluations, did not assess these patients for EEG evidence of cerebral irritability23The study reported here was undertaken, therefore, to assess the effects, if any, of several commonly employed intravenous induction agents on both the threshold for enflurane-indueed EEG seizures and on the continuation of established EEG seizure activity. METrIODS AND RESULTSEight adult female cats were used for a total of 28 experiments. These animals were chronic preparations with permanently implanted EEG recording electrodes.Each animal was provided with four stainless steel screws resting on the fi'ontal dura. Subcortical structures were implanted with four bipolar electrodes, corresponding to two bilateral sites. Each animal had two subcortical sites selected fi'om brain stem reticular formation, amygdala or hippocampal nuclei.Implantation was undertaken with intraperitoneal pentobarbitone anaesthesia (35 mg/kg). The animals were mounted in a David Kopf stereotaxie apparatus and the subcortical sites were implanted according to the coordinates of Jasper. la From the

Enflurane-Induced Burst Firing of Hippocampal Ca 1 Neurones

“…The results agree with recent (Stevens et al, 1984) and earlier (Darimont and Jenkins, 1977;Black, 1979) observations in mammalian in vivo preparations. These studies reported both excitatory and depressant actions of enflurane on CNS electrical activity.…”

The Biphasic Pattern of the Convulsive Property of Enflurane in Cats

“…A review of previous reports on the actions of enflurane on neuro-electrical activities shows that most reports cover a relatively narrow concentration range, 0-3.5%, and report a dose-related monophasic stimulation of the CNS (Steen and Michenfelder, 1979). Neigh, Garman and Harp (1971) and Darimont and Jenkins (1977) reported a biphasic pattern in the change in spontaneous EEG spike frequency, which was confirmed by the present study, but these reports did not examine the convulsive property.…”

Postoperative pseudostatusNot everything that shakes is epilepsy

“…Seizure‐like movements frequently occur in association with general anaesthesia. There is experimental evidence that many anaesthetic drugs can lower the neuronal ‘seizure threshold’ [5, 6]. Despite this, postoperative epileptic seizures are extremely rare [7, 8].…”