++
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.
++++
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 report was ...