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INTRODUCTION

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This chapter reviews various factors that may contribute to neurologic complications after peripheral nerve blocks (PNBs) and suggests principles of practice and implications of monitoring modalities to mitigate the risk of neurologic complications.

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ANATOMY CONSIDERATIONS OF PERIPHERAL NERVE BLOCK–RELATED NERVE INJURY

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A nerve is a distinct organ comprising neural tissue, a specific connective tissue stroma, and a designated blood supply (Figure 60–1). Nerve cells, or neurons, are composed of a cell body, dendrites, and an axon. The axon is a cytoplasmic extension of the neuron that transmits electrical signals along its length from the cell body proximally to anywhere from just a few millimeters up to nearly 1 m distally. Most peripheral nerves can transmit both afferent motor and efferent sensory signals.

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Figure 60–1.

Human sciatic nerve. Scanning electron microscopy. (Reproduced with permission from Reina MA: Atlas of Functional Anatomy for Regional Anesthesia and Pain Medicine. Heidelberg: Springer; 2015.)

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In the peripheral nervous system, the vast majority of axons are myelinated, characterized by a sheath of Schwann cells that encase the axon in a layer of myelin (Figure 60–2). The Schwann cells are interrupted at interposed spaces, known as the nodes of Ranvier, where the process of depolarization and repolarization occurs during the saltatory propagation of the action potential. Together with its myelin sheath, each axon is bound by a thin layer of connective tissue called an endoneurium (Figure 60–3) and then termed a nerve fiber.

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Figure 60–2.

A: Unmyelinated axon of a human nerve rootlet. B: Myelinated axon of a human sciatic nerve. Transmission electron microscopy. (Reproduced with permission from Reina MA: Atlas of Functional Anatomy for Regional Anesthesia and Pain Medicine. Heidelberg: Springer; 2015.)

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Figure 60–3.

Endoneurium. Myelinated axons enveloped by endoneurium obtained from a human sciatic nerve. A: Transmission electron microscopy. (Reproduced with permission from Reina MA: Atlas of Functional Anatomy for Regional Anesthesia and Pain Medicine. Heidelberg: Springer; 2015.) B: Scanning electron microscopy. (Reproduced with permission from Reina MA: Atlas of Functional Anatomy for Regional Anesthesia and Pain Medicine. Heidelberg: Springer; 2015.)

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Nerve fibers are organized into groups called fascicles (Figure 60–4). Within each fascicle, the nerve fibers form an intraneural plexus in which the axons take different positions along their path (Figure 60–5). In the vicinity of joints, the fascicles are thinner and more numerous and tend to be surrounded by a greater amount of connective tissue, which reduces the vulnerability of the fascicles to insults such as pressure and stretching.

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Figure 60–4.

Fascicles of human median nerve. (Used with ...

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