CHAPTER 84: Peripheral Nerve Blocks

INTRODUCTION

The peripheral nervous system consists of numerous individual nerves, nerve trunks, nerve plexuses, and ganglia. This chapter discusses the blockade of somatic peripheral nerves. The sympathetic and visceral nerve blocks are discussed separately. The blockade of peripheral somatic nerves is the hallmark of regional anesthesia. This may be done for the facilitation of surgery as a sole technique or in combination with general anesthesia. Peripheral nerve blocks can be continued into the postoperative period via infusion through catheters for the purpose of continued postoperative pain relief. Excellent perioperative analgesia may help reduce the possibility of development of chronic pain.^1,2 Additionally, some evidence indicates that regional anesthesia may have a role in reducing the recurrence of disease in patients undergoing oncologic surgery.³

In the field of chronic pain management, peripheral nerve blocks are useful in the diagnosis of pain conditions. At times these may provide pain relief beyond the duration of the local anesthetic itself and hence serve a therapeutic purpose.⁴ Various adjuvants such as clonidine, steroids, and vasoconstrictors may be added to the local anesthetic to prolong the duration of the nerve block. In some select circumstances, once the pain generating nerve is identified, neurolysis of the nerve via chemical or thermal techniques can be done. Chemical neurolysis is often done with alcohol or phenol, and in general, use of these agents is reserved for patients with terminal illness because of the risk of recurrent pain that may be worse, as well as the risk of permanent neurologic sequelae. Thermal techniques such as medial branch thermal neurotomy and cryoablation of neuromas are useful in the management of chronic pain.⁵

Historically, peripheral nerve blocks were often performed as a blind technique using surface anatomy landmarks, as well as feel. The introduction of nerve stimulation techniques was instrumental in improving the success of peripheral nerve blockade. With this technology, the proximity of the needle tip to the neural tissue can be objectively verified. Recently, with the introduction of ultrasound, the nerve can be visually identified and a needle placed next to it in real time. The spread of the medication around the nerve can also be visualized in real time. The availability of portable ultrasound machines has led to exponential use of this modality in the performance of peripheral nerve blocks. There has been increased use of ultrasound guidance in the field of chronic pain management as well. Interventional pain management, however, has a strong reliance on fluoroscopy in the performance of peripheral nerve blocks near the spine because bony landmarks serve well to predict the location of the nerve, and ultrasound has limited utility.

The success of a nerve block depends on several factors. First, it is key that the purpose of performing the nerve block is clearly understood both by the patient and the physician. Second, in the case of diagnostic blocks, knowledge of the factors ...