Abstract
Purpose
To determine the effect of isoflurane on motor evoked potentials (MEP) in a new animal model designed to verify the applicability of MEPs in brachial plexus surgery, and to compare the results with previous reports in other animals.
Methods
In seven goats, anesthesia was induced with 3 mg·kg−1 ketamine iv and maintained with nitrous oxide 40% in oxygen and 2 μg·kg−1·hr−1 fentanyl iv. The MEP were performed with two subcutaneous needle electrodes placed over the occiput (cathode) and the nasion (anode), with their plugs connected to the power output of a Digitimer D 180 electrical stimulator, connected to the trigger input of an electromyograph (model 8400, Cadwell Laboratories, Inc., Kennwick, Washington). Activation of the Digitimer caused central stimulation of the motor cortex, evoking baseline compound muscle action potentials (CMAPs) which were recorded from the left triceps muscle. Subsequently, isoflurane 2% was administered together with repeated central stimulation at 30 sec intervals.
Results
Onset of I-(indirect) waves increased from median 15,8 msec to median 26,8 msecP = 0,018 (latency increase ranged from: 9 to 11.5 msec), while peak-to-peak amplitudes decreased and subsequently disappeared. D-(direct) waves showed no latency increase, and finally disappeared as well. After disappearance of CMAPs, isoflurane administration was stopped and MEP repeated. The CMAPs reappeared (range: 210–360 sec) and regained initial peak-to-peak amplitudes and latencies.
Conclusion
These animal studies suggest that isoflurane should not be used during the recording of MEPs.
Résumé
Objectif
Déterminer l’effet de l’isoflurane sur les potentiels évoqués moteurs (PEM) chez un nouveau modèle animal conçu pour vérifier l’applicabilité des PEM à l’opération du plexus brachial, et comparer les résultats avec ceux d’articles antérieurs chez d’autres animaux.
Méthode
L’anesthésie a été induite chez sept chèvres avec 3 mg·kg−1 de kétamine iv et maintenue avec du protoxyde d’azote à 40% dans de l’oxygène et 2 μg·kg−1·hr−1 de fentanyl iv. Les PEM ont été réalisés avec deux aiguilles-électrodes sous-cutanées placées au niveau de l’occiput (cathode) et sur le nasion (anode) branchées à la borne d’entrée d’un électromyographe (modèle 8400, Cadwell Laboratories, Inc., Kennwick, Washington), leurs connecteurs étant reliés à la borne de sortie d’un stimulateur électrique Digitimer D 180. L’activation du Digitimer a provoqué une stimulation centrale du cortex moteur, évoquant les potentiels de base d’action musculaire combinée (PAMC) qui étaient enregistrés à partir des réactions du triceps gauche. Par la suite, l’isoflurane à 2% était administré en même temps qu’une stimulation centrale répétée à intervalles de 30 s.
Résultats
L’installation des ondes I (indirectes) a montré un accroissement d’une médiane de 15,8 msec à une médiane de 26,8 msecP = 0,018 (l’augmentation du temps de latence a varié de 9 à 11,5 msec), tandis que les amplitudes entre les pics ont baissé, puis disparu. Les ondes D (directes) n’ont pas présenté d’accroissement du temps de latence et ont finalement disparu également. Après la disparition des PAMC, l’administration d’isoflurane a été stoppée et le PEM, répété. Les PAMC sont réapparus (intervalle: 210–360 s) et ont affiché de nouveau les amplitudes entre les pics et les temps de latence initiaux.
Conclusion
Ces études animales suggèrent que l’isoflurane ne doit pas être utilisé pendant l’enregistrement des PEM.
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Andel, H., Bayer, G.S., Ciovica, R. et al. Depressive effect of isoflurane on motor evoked potentials in the Nubian goat. Can J Anesth 47, 81–86 (2000). https://doi.org/10.1007/BF03020739
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DOI: https://doi.org/10.1007/BF03020739