Chapter 5

Eliciting paresthesia or nerve stimulation are commonly used methods for localizing nerves prior to the injection of local anesthetic. Paresthesia is thought to result from mechanical stimulation of the nerve, resulting in a sensory feeling described as “an electric current” or “shock” in the sensory distribution of the nerve that is being touched. As such, paresthesia can indicate that the needle is in close proximity to the nerve and may be a warning sign of impending mechanical injury, should the needle be further advanced. In contrast, nerve stimulation techniques rely on the use of electric current to elicit motor stimulation of nerves and confirm the proximity of the needle to the nerve.

Electrical nerve stimulation is currently the most common technique for localizing nerves prior to the injection of local anesthetic. Depolarizing the nerve membrane results in contraction of the effector muscles (motor fibers) or in paresthesias (sensory fibers) in the distribution of the nerve. These responses can be used to confirm the proximity of a needle or catheter to the nerve. This localization technique for nerve blocks was first described by von Perthes in 1912; however, it has only gained wider acceptance in regional anesthesia over the last two decades.1 Subsequently, a number of researchers have further improved and developed this technique. Pearson introduced the concept of using an insulated needle for the localization of nerves;2 however, Montgomery and colleagues later demonstrated that ordinary uninsulated needles could also be used to localize nerves, albeit with a higher current.3 The use of a portable transistorized nerve stimulator with a variable current output was first introduced by Greenblatt and Denson.4 Ford and associates further emphasized the important characteristics of electrical nerve stimulators and the differences between insulated and uninsulated needles.5,6 In recent years, the same electrical stimulation principles have been applied for new uses such as percutaneous electrode guidance (PEG),7–10 confirmation of epidural catheter placement,11–13 and peripheral catheter placement for continuous regional anesthesia.14 The clinical relevance of the duration of the stimulating current and optimal placement of the return (skin) electrode have also been determined.15

In order to use nerve stimulation effectively a basic knowledge of the electrophysiologic principles is necessary. The following discussion is based on the commonly accepted theoretical and practical concepts of nerve stimulation. However, our understanding of the mechanisms of nerve stimulation is still incomplete. Thus, the reader should remain cognizant of the fact that current literature still has conflicting concepts and recommendations regarding several aspects of nerve stimulation.16

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Clinical Pearls
 Uncomfortable motor response to nerve stimulation can be avoided by using a low-intensity stimulating current with a short pulse width. However, when a higher current is used, preferential stimulation of the motor nerve may be lost Therefore, the best method to avoid discomfort on nerve stimulation is to limit the energy (E) or current intensity (I) during ...

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