Epidural anesthesia:
To determine the ion channel blocked by lidocaine, it is necessary to asses which ion channels are essential in nerve function. Between action potential conductance of potassium ion and chlorine ion high at rest, mediated respectively by potassium and chlorine ion in the nerve membrane. The total charge between the inside and outside of the cell is driven toward the potassium and chlorine ion reversal potentials(Hui, Varadharajan, ., Yousefzadeh, 2017). during the upstroke of the nerve action potential voltage-gated sodium ion are more critical. The sodium channel opens in response to depolarization, and this opening increases depolarization towards the reversal potential. In a depolarized cell, there is an increased probability that sodium ion channels will open, therefore increasing the likelihood that it will be inactivated.
When the cell depolarizes, sodium activation gates open. This delays the inactivation cell repolarizes (with the help of potassium flowing out of the cell through its channel). Repolarization rests the sodium channels’ activation gates, allowing the cell to generate another action potential (Naruse, Uchizaki, Mimura et al.,2016). Local anesthetic and lidocaine block voltage-gated channels in nerve membranes. At high concentrations, upstroke is prevented. Hence no action potential occurs. While at low concentrations, sodium channel blockage leads to a slow rate rise of the upstroke of the action potential.
An action potential is propagated along sensory nerve axons by the spread of local currents from active depolarized areas. This local depolarizing current is triggered by inward sodium current of the upstroke of the action potential. Blocked voltage-gated sodium channels by lidocaine, the inward sodium current of the upstroke of the action potential does not occur (Einhorn, & Habib, 2016). This sodium channel blockage results in the prevention of the propagation of the action potential, which depends on depolarizing inward current.
Reference
Naruse, S., Uchizaki, S., Mimura, S., Taniguchi, M., Akinaga, C., & Sato, S. (2016). Pressure ulcers caused by long-term keeping of the same body position during epidural labour analgesia. Masui. The Japanese journal of anesthesiology, 65(6), 643-645.
Hui, C., Varadharajan, R., Yousefzadeh, A., Davies, S., & Siddiqui, N. T. (2017). Aseptic techniques for labour epidurals: A survey and review of neuraxial anesthesia practice. Canadian Journal of Infection Control, 32(1), 25-30.
Einhorn, L. M., & Habib, A. S. (2016). Evaluation of failed and high blocks associated with spinal anesthesia for cesarean delivery following inadequate labour epidural: a retrospective cohort study. Canadian Journal of Anesthesia/Journal Canadien d’anesthésie, 63(10), 1170-1178.