Introduction to Nerve Blocks

Leonard V. Bunting, MD, FACEP

I. Overview

Nerve blocks offer many advantages over traditional methods of anesthesia/analgesia in the ED.

• Target relief to a specific site or region
• Provide pain relief for up to 24 hours
• Little to no burden on ancillary staff or post-procedure observation
• High patient satisfaction^1-3
• Decreased length of stay¹

Illustration 1. Anatomy of Peripheral Nerves

Indications

• Acute regional pain management (fractures, burns, infections, chronic pain)
• Anesthesia of the extremity for a procedure (suturing, I&D, fracture/joint reduction, burn debridement)
• Alternative to procedural sedation
• Alternative to narcotics in certain patient populations (extremes of age, head injuries, altered mental status, patients on buprenorphine)

Contraindications

• Allergy to local anesthetic agents
• Active infection at injection site
• Risk of compartment syndrome or need to monitor neurologic function
• Uncooperative patient
• Pre-existing neurologic deficit that could prevent the patient from communicating paresthesia or pain during the nerve block
• Obesity obscuring optimal visualization
• Coagulopathy (relative)

II. Anatomy of Peripheral Nerves

Peripheral nerves are composed of bundles of neurons, or nerve fascicles, which are enclosed by a connective tissue called the perineurium.

• Fascicles are further bundled and held together by the loose connective tissue of the endoneurium.
• This nerve complex is enclosed within epineurium, the outermost layer of a peripheral nerve.

III. Scanning Techniques and Normal Findings

Normal Sonographic Appearance of Peripheral Nerves

• Classically, nerves have a honeycomb-like appearance in cross section caused by bundling of hypoechoic nerve fascicles within hyperechoic peri- and endoneurium.
• Distal or smaller nerves contain smaller amounts of myelinated axons and can instead look like the cut end of a rope and mimic the appearance tendons.
• Nerves may be oval, round or triangular and often change shape along their course.
• The overall conformation of a peripheral nerve depends on its course and surrounding tissue.

Figure 1a. Ultrasound Image of Peripheral Nerves

Figure 1b. Ultrasound Image of Peripheral Nerves With Labels

Identifying Nerves

• A linear array transducer is generally used to identify peripheral nerves.
• Nerves are best seen in transverse or cross-section.
• Nerves can exhibit strong anisotropy (Video 1). 
  • Anisotropy refers to the changes in echogenicity of a structure as the angle of insonation is changed.
  • Care must be taken to adjust the angle of insonation to ensure optimal nerve visualization.
  • Tendons, ligaments and muscle also exhibit anisotropy.

Video 1. Anisotropy

• Nerves can be hard to identify on ultrasound.
  • Tendons, muscle and fascial planes can all look like nerves or hide them.
  • Nerves are often found by their association with more easily identified structures such as blood vessels, bone or muscles.
  • Multiple, rapid passes along the expected course of a nerve may highlight its location.
  • Identifying a nerve distally and following it back to the site of intervention can also be helpful.

V. Pearls and Pitfalls

• General Procedure Setup
• Needle Choices
• In-Plane vs Out-of-plane Approach
• Injection Precautions

VI. References

1. Stone MB, Wang R, Price DD. Ultrasound-guided supraclavicular brachial plexus nerve block vs procedural sedation for the treatment of upper extremity emergencies. Am J Emerg Med. 2008;26(6):706-10.
2. Blaivas M, Lyon M. Ultrasound-guided interscalene block for shoulder dislocation reduction in the ED. Am J Emerg Med. 2006;24(3):293-6.
3. Beaudoin FL, Nagdev A, Merchant RC, Becker BM. Ultrasound-guided femoral nerve blocks in elderly patients with hip fractures. Am J Emerg Med. 2010;28(1):76-81.

VII. Additional Reading

• Wilson JE, Pendleton JM. Oligoanalgesia in the emergency department. Am J Emerg Med. 1989;7(6):620-3.
• McQuay HJ, Carroll D, Moore RA. Postoperative orthopaedic pain – the effect of opiate premedication and local anesthetic blocks. Pain. 1988;33(3):29–5.
• Liebmann O, Price D, Mills C, Gardner R, Wang R, Wilson S, Gray A. Feasibility of forearm ultrasound-guided nerve blocks of the radial, ulnar and median nerves for hand procedures in the emergency department. Ann Emerg Med. 2006;48(5):558-62.
• Pogatzki-Zhan EM, Zahn PK. From preemptive to preventive analgesia. Current Opinion Anaesthesiol. 2006;19(5):551-5.