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Ultrasound Guided Nerve Blocks

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Nerve Block Navigator

Leonard V. Bunting, M.D.

Overview

Emergency physician performed ultrasound-guided regional anesthesia is an evolving field that offers many potential benefits in the emergency setting:  Analgesia can be targeted specifically to the region of pain and provide relief for many hours, large volumes of local anesthetic can be avoided and there is also less need for general sedation without the increased morbidity to patients.  In addition, by providing an alternative to procedural sedation, there seems to be a decreased ED-length of stay, shortened post-procedure observation periods with reduced need for ED-nursing care, and high patient satisfaction. (1-7)

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Ultrasound Slider 1:  Ultrasonographic Appearance of a Peripheral Nerve. Use slider to reveal anatomy.

Indications

- Acute pain management of the extremities
- Anesthesia of the extremity for procedures
- Alternative to procedural sedation
- Alternative to narcotics in certain patient populations (e.g. head injured patient, patients with  
  concomitant mental status change, patients given buprenorphine)

Contraindications

- Allergy to local anesthetic agents
- Active infection at the site of injection
- Injuries at risk of compartment syndrome
- Uncooperative patient
- Pre-existant neurologic deficit
- Extreme obesity obscuring optimal ultrasonographic visualization
- Anticoagulation (relative)


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Illustration 1:  Nerve Block Navigator.

Selection of peripheral nerve blocks with relevance to emergency medicine. Roll-over the desired area for peripheral anesthesia and click on the hyperlink to view a specific nerve block chapter.

 

II. Anatomy of Peripheral Nerves

The peripheral nervous system (PNS) connects the central nervous system (CNS; = brain and spinal cord) with visceral and somatic tissues and organs.  The PNS can be subdivided into motor, sensory and autonomic components.  The majority of sensory nerves arise from dorsal root ganglia found adjacent to the spinal column.  Sensory nerve fibers (myelinated and non-myelinated axons) project from the dorsal root ganglia in bundles, 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 and an epineurium, the outermost layer of a peripheral nerve.  Peripheral nerves project to target tissues where they branch and terminate in either specialized (e.g. Pacinian corpuscles) or nonspecialized (free nerve endings) structures that sense chemical and mechanical stimuli.   Upon activation, sensory nerves transmit action potentials back to the CNS and initiate sensations and reflexes that are relayed back to the periphery by the motor nerves innervating the musculoskeletal system and through the autonomic nerves innervating all tissues and organs.  Peripheral nerves hence carry both sensory and motor nerves and innervate specific regions of the body.  Knowledge of this anatomy is essential when considering peripheral nerve blocks.

Illustration 2:  Schematic view of a peripheral nerve.

The specific anatomical area of nerve innervation will be covered for each nerve block separately. For a specific desired region of anesthesia see illustration 1 and table 1 and click on a nerve block to move directly to the chapter.


Table 1: Peripheral nerve blocks – Distribution of anesthesia

Type of Block

General Distribution of Anesthesia

Interscalene Plexus Block

Shoulder, upper arm, elbow and forearm

Supraclavicular Plexus Block

Upper arm, elbow, wrist and hand

Infraclavicular Plexus Block

Upper arm, elbow, wrist and hand

Axillary Plexus Block

Forearm, wrist and hand. Elbow if including musculocutaneous nerve.

Median Nerve Block

Hand and Forearm

Radial Nerve Block

Hand and Forearm

Ulnar Nerve Block

Hand and Forearm

Femoral Nerve Block

Anterior thigh, femur, knee and skin anesthesia over the medial aspect of the leg below the knee

Popliteal Nerve Block

Anesthesia to the foot and ankle as well skin anesthesia over the posterior lateral portion of the lower extremity distal to the knee.

Tibial Blocks

Foot and ankle

Deep Peroneal Blocks

Foot

Saphenous Nerve Block

Foot

Sural Nerve Block

Foot


III. Scanning Techniques and Normal Findings

Normal Sonographic Appearance of Peripheral Nerves

For all peripheral nerve blocks, a high frequency linear array ultrasound (9-18 MHz) is used. Peripheral nerves have a variable sonographic echotexture that is affected by the surrounding tissue.  Classically, nerve fascicles itself appear hypoechoic embedded within a more hyperechoic and homogenous perineurium and endoneurium.  When grouped together and viewed in a transverse plane, this gives peripheral nerves their classic ‘honeycomb’ appearance.  Occasionally, particularly at distal and smaller segments, nerves contain smaller amounts of myelinated axons and can mimic tendons.  
The overall conformation of a peripheral nerve depends on its course and surrounding tissue. Nerves may be oval, round or triangular and often change shape along their course. For this reason, it is sometimes helpful to identify the nerve distally and follow it back to the site of intervention. Nerves may be identified from blood vessels by testing them for non-compressibility and by the use of Doppler.


V. Pearls and Pitfalls

 

VI. References

  1. Wilson JE, Pendleton JM.
    Oligoanalgesia in the emergency department. Am J Emerg Med. 1989;7(6):620–3.

  2. McQuay HJ, Carroll D, Moore RA.
    Postoperative orthopaedic pain – the effect of opiate premedication and local anesthetic blocks. Pain. 1988;33(3):29–5.

  3. 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.

  4. Pogatzki-Zhan EM, Zahn PK.
    From preemptive to preventive analgsia. Current Opinion Anaesthesiol. 2006;19(5):551-5. Review.

  5. 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.

  6. Blaivas M, Lyon M.
    Ultrasound-guided interscalene block for shoulder dislocation reduction in the ED. Am J Emerg Med. 2006;24(3):293-6.

  7. 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.

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