Skip to Main Content

++

Basic Considerations: Introduction

++

Although there are relatively few published reports of anesthesia-related nerve injury associated with peripheral nerve blocks (PNBs), it is likely that the commonly cited incidence (0.4%) of neurologic injury is underestimated owing to underreporting.1–3 Most complications of PNBs were reported with upper extremity blocks. The less frequent clinical application of lower extremity nerve blocks may be the main reason why there are even fewer reports of anesthesia-related nerve injury associated with lower extremity PNBs compared with upper extremity PNBs.4 Although neurologic complications after PNBs can be related to factors associated with the block technique (eg, needle trauma, intraneuronal injection, neuronal ischemia, and toxicity of local anesthetics), a search for other common causes should include positional and surgical factors (eg, positioning, stretching, retractor injury, ischemia, and hematoma formation). In some instances, the neurologic injury may be a result of a combination of these factors.

++

In all four sections of this chapter, mechanisms and consequences of acute neurologic injury related to the nerve block procedure are discussed and, where appropriate, methods and techniques to reduce the risk of complications are suggested. Specific nerve injuries with upper and lower nerve block techniques, neuraxial anesthesia, and local anesthetic toxicity are discussed elsewhere in this volume.

++

Functional Histology of the Peripheral Nerves

++

Knowledge of the functional histology of the peripheral nerve is important to understand the mechanisms of peripheral nerve injury; the reader is referred to Chapters 3 and 4 for more in-depth discussion on this subject. Here we briefly review salient features of the organization of the peripheral nerves. A peripheral nerve is a complex structure consisting of fascicles held together by the epineurium, an enveloping, external connective sheath (Figure 69–1). Each fascicle contains many nerve fibers and capillary blood vessels embedded in a loose connective tissue, the endoneurium.5 The perineurium is a multilayered epithelial sheath that surrounds individual fascicles and consists of several layers of perineural cells. Therefore, in essence, a fascicle is a group of nerve fibers or a bundle of nerves surrounded by perineurium. Of note, fascicles can be organized in one of three common arrangements: monofascicular (single, large fascicle); oligofascicular (few fascicles of various sizes); and polyfascicular (many fascicles of various sizes).6

++
Fig. 69-1
Graphic Jump Location

Histology of the peripheral nerve. Shown is a large fascicle of the peripheral nerve with its axons, surrounded by perineurium, epineurium, and nourishing blood vessels.

++

Nerve fibers can be myelinated or unmyelinated; sensory and motor nerves contain both in a ratio of 4:1, respectively. Unmyelinated fibers are composed of several axons, wrapped by a single Schwann cell. The axons of myelinated nerve fibers are enveloped individually by a single Schwann cell. A thin layer of collagen fibers, the endoneurium, surrounds the individually myelinated or groups of unmyelinated fibers.

++

...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.