Abstract
Purpose
The use of 10–15 μg epinephrine as an epidural test-dose is controversial. Isoproterenol would be a better alternative. However before 5μg isoproterenol can be incorporated in an epidural test-dose, neurotoxicological studies have to be performed. The present study was designed to assess spinal somatosensory evoked potentials (spinal SSEP) before and after epidural isoproteronol.
Methods
Spinal SSEPs were recorded before, 30 min after, and 72 hr after 50 μg isoproterenol were given epidurally (L3–4) to six chronically instrumented awake sheep. The spinal SSEPs after epidural (L3–4 administration of 15 ml lidocaine 2% were used to evaluate the model. The SSEPs were generated by transcutaneous stimulation of the sciatic nerve in the thigh. Spinal SSEPs were recorded directly from the spinal cord at vertebra T12 using a monopolar epidural electrode referenced to a subcutaneous needle electrode in the adjacent paraspinal area.
Results
Thirty minutes and 72 hr after epidural injection of 50 μg isoproterenol the latency and the amplitude of the SSEP waves were similar to baseline values. After lidocaine, no SSEPs could be generated in three sheep while in three sheep the latency of wave 2 (W2) was prolonged and the amplitude diminished.
Conclusion
Administration of epidural isoproterenol did not affect spinal SSEPs in this study indicating an absence of neurotoxic side effects.
Résumé
Objectif
L’utilisation de 10–15 μg d’épinéphrine comme dose-test de l’anesthésie épidurale est contestée. Lisoprotérénol devrait être une meilleure solution de rechange. Cependant, avant d’incorporer 5 μg d’isoprotérénol à une dose-test épidurale, il faut effectuer des études de neurotoxicité. L’étude actuelle visait à mesurer les potentiels évoqués somatosentoriels (SS) spinaux avant et après de l’isoprotérénol épidural.
Méthodes
Les SSEP spinaux ont été enregistrés avant, 30 min après et 72 h après l’administration épidurale de 50μg d’isoprotérénol (L3-L4) à six préparations de moutons éveillés. Les SSEP spinaux enregistrés après l’administration de 15 ml de lidocaïne 2% ont servi à valider le modèle. Les SSEP ont été générés par stimulation transcutanée du nerf sciatique au niveau de la cuisse. Les SSEP spinaux ont été enregistrés directement sur la moelle au niveau de T12 avec une électrode unipolaire ; l’électrode de référence était une aiguille sous-cutanée insérée dans la région paraspinale adjacente.
Résultats
Trente minutes et 72 h après l’injection épidurale de 50 μg d’ isoprotérénol, la latence et l’amplitude des ondes SSEP étaient identiques aux valeurs initiales. Après la lidocaïne, les SSEP ne pouvaient être générés chez trois moutons alors que chez les trois autres, la latence de l’Onde 2 (W2) était prolongée et son amplitude diminuée.
Conclusion
Pendant cette étude, l’administration d’isoprotérénol épidural n’a pas affecté les SSEP spinaux, ce qui démontre l’absence d’effets neurotoxiques.
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The study was performed at the Center of Experimental Surgery and Anesthesiology, University Hospitals, Katholickc Universiteit Leuven.
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Marcus, M.A.E., Bruyninckx, F.L., Vertommcn, J.D. et al. Spinal somatosensory evoked potentials after epidural isoproterenol in awake sheep. Can J Anesth 44, 85–89 (1997). https://doi.org/10.1007/BF03014330
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DOI: https://doi.org/10.1007/BF03014330