Chapter 46

Contrary to common, oversimplified representations by medical illustrators, the arrangement of peripheral nerves and plexuses is quite complex. Various tissue compartments contain connective tissue and fat; terminal branches of plexuses and nerves divide and separate frequently, and the different branches may run at some distance from one another. Accordingly, once injected at a particular site, the local anesthetic molecules have to diffuse through several barriers before reaching the nerves, the first barrier being the distance between the injection site and each branch.

In regional anesthesia, the most frequently used strategy for overcoming this “spatial dispersion” of nerve branches is to place the needle somewhere close to the nerves and then inject a volume of local anesthetic large enough to spread toward desired different branches. This practice has been traditionally taught and clinically used for decades throughout the development of regional anesthesia. However, with the advent of modern nerve stimulators and nerve-stimulating techniques, electrolocation can be utilized to augment selectivity in nerve location, increase the success rate, and minimize the amount of local anesthetic required to accomplish a nerve block.

This chapter will discuss general principles of multistimulation for the commonly used peripheral nerve block procedures. For more discussions on anatomy and techniques, the reader is referred to the respective technique and detailed description of the anatomy elsewhere in this book.

The use of a nerve stimulator makes it possible to readily identify different muscular twitches during block placement, by simply redirecting the stimulating needle according to the anatomic topography of each nerve block considered, using the so-called multiple injection technique. The rationale of the multiple-injection technique is to specifically and separately localize and block each major nerve required for surgical anesthesia using a small volume of local anesthetic solution.

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 The rationale of the multiple-injection technique is to specifically and separately localize and block each major nerve required for surgical anesthesia using a small volume of local anesthetic solution.

The needle is inserted as usual based on classical anatomic landmarks, with the nerve stimulator set at 1- to 1.5-mA intensity until the initial motor response is obtained. Thereafter, the intensity of the stimulating current is progressively reduced to less than 0.5 mA while maintaining the twitch response, at which point an injection of 5 to 7 mL of local anesthetic solution is made. When the desired component (nerve) is blocked, the current intensity of the nerve stimulator is again increased to 1 to 1.5 mA, and the needle is redirected according to the anatomic relationship among the individual components of the nerve being blocked. When the twitch of another component of the nerve is accomplished, an additional 5–7 mL of local anesthetic is injected. This maneuver is then repeated for all the main branches of the nerve required for surgery.

Several clinical studies have demonstrated the advantages of the multiple-injection technique. The first ...

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