Abstract
Purpose
Using electrical epidural stimulation, a current of 1 to 10 mA is required to confirm the presence of the tip of an epidural catheter in the epidural space. The purpose of this study was to examine the hypothesis that the threshold current required to elicit a motor response in the intrathecal space is significantly lower than that in the epidural space in a porcine model.
Methods
Four 20-kg pigs were used in this experiment. Eighteen gauge, insulated, Tuohy needles were advanced into the epidural space using the loss of resistance technique at five different spinal levels in each pig. When the epidural space was entered, an electrical current was applied to the needle and increased progressively until a motor response was elicited. The needle was then further advanced until cerebrospinal fluid (CSF) was observed or until the needle had been advanced a maximum of 1 cm. At this point, the current was reapplied and increased until motor activity was evident.
Results
A total of 20 needles were inserted in four pigs. The current required to produce a motor response in the epidural space was 3.45 ± 0.73 mA (mean ± SD). The current required to produce a motor response in the intrathecal space (entry confirmed by the presence of CSF) was 0.38 ± 0.19 mA (mean ± SD). Two needles were advanced 1 cm without obtaining CSF but the current thresholds were similar to those obtained when CSF was evident (0.4 mA and 0.3 mA, respectively).
Conclusion
The threshold current of an insulated needle required to elicit a motor response in the intrathecal space, was significantly (P < 0.01) lower than that in the epidural space in a porcine model.
Résumé
Objectif
En utilisant une stimulation péridurale électrique, un courant de 1 à 10 mA est nécessaire pour confirmer la présence de la pointe d’un cathéter dans l’espace péridural. Notre objectif était de vérifier l’hypothèse voulant que le courant seuil nécessaire pour obtenir une réponse motrice dans l’espace intrathécal soit significativement plus faible que dans l’espace péridural chez un modèle porcin.
Méthode
Quatre porcs de 20 kg ont été utilisés. Des aiguilles Tuohy isolées, de calibre 18, ont été poussées dans l’espace péridural selon la technique de perte de résistance à cinq niveaux différents chez chaque animal. Une fois l’aiguille introduite, un courant électrique était appliqué et augmenté progressivement jusqu’à l’obtention d’une réaction motrice. L’aiguille était ensuite avancée plus loin jusqu’à ce qu’on observe du liquide céphalorachidien (LCR) ou de 1 cm tout au plus. À ce point, le courant était réappliqué et augmenté jusqu’à ce que l’activité motrice soit évidente.
Résultats
Un total de 20 aiguilles ont été insérées chez quatre porcs. Le courant requis pour produire une réponse motrice dans l’espace péridural a été de 3,45 ± 0,73 mA (moyenne ± écart type). Le courant requis dans l’espace intrathécal (entrée confirmée par la présence de LCR) a été de 0,38 ± 0,19 mA (moyenne ± écart type). Deux aiguilles ont été poussées de 1 cm sans qu’on observe de LCR, mais les courants minimaux ont été similaires à ceux qu’on a obtenus en présence de LCR (0,4 mA et 0,3 mA, respectivement).
Conclusion
Le courant seuil, transmis par une aiguille isolée, nécessaire pour produire une réponse motrice dans l’espace intrathécal a été significativement (P < 0,01) plus faible que dans l’espace péridural chez un modèle porcin.
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Supported in part by the Education and Research Fund, Department of Anesthesiology and Pain Medicine, University of Alberta Hospitals, Edmonton, Canada, and Clinical Investigatorship Award, Alberta Heritage Foundation for Medical Research, Alberta, Canada.
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Tsui, B.C.H., Wagner, A. & Finucane, B. The threshold current in the intrathecal space to elicit motor response is lower and does not overlap that in the epidural space: a porcine model. Can J Anesth 51, 690–695 (2004). https://doi.org/10.1007/BF03018427
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DOI: https://doi.org/10.1007/BF03018427