Issue 26, December 2008 Targeting Anesthesia Care

Ultrasound-Guided Upper Extremity Nerve Blocks

Correspondence: Dr. M. Morimoto, MD, Department of Anesthesiology, New York University School of Medicine (E-mail and other contact info can be obtained from CWWJ’s Editor-in-Chief).

Key Words: Ultrasound, regional anesthesia, upper extremity, peripheral nerve blocks.
Running title: Ultrasound-Guided Upper Extremity Nerve Blocks.

Clinical Window Web Journal #26: Ultrasound Guided Upper Extremity Nerve Blocks (December 2008). ISSN 1795-6269.

Introduction

Conventional peripheral nerve blocks are frequently performed guided only by surface anatomical landmarks and operator experience, an often tedious and inaccurate technique.(1) The failure rate, depending on the type of block, can be as high as 20%.(2)

Ultrasound technology is still developing; however, it has already shown some potential benefits over conventional techniques. The first ultrasound-guided nerve block was described by LaGrange in 1978 and, since its introduction, the interest in this field has been growing steadily.(3) In 2003, Williams reported a higher success rate and faster performance with the use of ultrasound in performing supraclavicular brachial plexus blocks when compared to conventional nerve stimulator techniques.(4) As ultrasound technology is becoming more accessible, portable, cheaper, and dependable, increasing numbers of practitioners are interested in learning and performing ultrasound assisted/guided peripheral nerve blocks. Visualizing the structures and the needle directly may offer higher success rates and fewer complications in ultrasound-guided nerve block techniques. In this article, four of the more commonly performed ultrasound-guided upper extremity blocks are described.

General guidelines

Expert knowledge of human anatomy and physiology, block techniques, anesthetic medications, and potential complications is necessary to successfully perform peripheral nerve blocks. The same standards that apply to conventional nerve block procedures should also be applied to ultrasound-guided nerve blocks. Informed consent from the patient must be obtained prior to performing the blocks. Strict sterile technique should be followed throughout the procedure. However, the selection of ultrasound probe, needle, and approaches is dependent on operator experience and individual patient requirements. Therefore, the techniques described should be viewed in that context, allowing for variation based on patient need, available equipment, and operator experience.

Interscalene Block

The brachial plexus originates from the nerve roots of C5 to T1. Once they emerge from the paravertebral foramen, the nerves travel in the interscalene groove formed between the anterior and middle scalene muscles as the roots become trunks. Interscalene blocks are typically performed at the level of the cricoid cartilage, usually at C6, in the interscalene groove.

Technical choices
Probe Selection: Linear Array
Frequency: 7 MHz or higher. Better results may be obtained using 10MHz or higher.
Needle Selection: 20 or 22 gauge 1½” block needle.

Technique: The patient is positioned supine with the head tilted slightly to the contralateral side. The ultrasound probe is then positioned in the short axis orientation on the interscalene groove so that the vascular structures, sternocleidomastoid, anterior scalene, and middle scalene muscles can be identified. Between the anterior and middle scalene muscles, several round structures with a hyper-echoic halo around them should be seen. These are the trunks of the brachial plexus. After local anesthetic infiltration to the skin, the block needle is introduced along the long axis of the probe.

The approach to the brachial plexus can be accomplished from either the anterior or posterior direction. However, the anterior approach may increase the risk of injury to the vascular structures. When reaching the brachial plexus between the anterior and middle scalene muscle, a “pop” is felt through the block needle as the neurovascular sheath is entered. The position of the needle is confirmed by observing the pattern of local anesthetic spread around the brachial plexus trunks on the ultrasound image as the injection is made.

Supraclavicular Block

As the brachial plexus travels farther along the interscalene groove to the level of the clavicle, nerve trunks intertwine with each other to form slightly more superficial structures known as nerve divisions. Supraclavicular block is typically performed at this location. Although it is a highly effective block, its popularity is limited because of the high rate of pneumothorax.

Technical choices
Probe Selection: Linear Array
Frequency: 10 MHz or higher
Needle Selection: 20 or 22 gauge 1½” block needle

Technique: The patient is positioned supine with the head tilted slightly to the contralateral side. The ultrasound probe is positioned in a coronal orientation where the patient’s neck and shoulder meet at the clavicle. Visualization of the subclavian vessels, first rib, and possibly lung tissue should be possible from this position. Brachial plexus divisions are seen as distinct round structures with a hyper-echoic halo around the artery. The divisions are typically arranged in a sheet-like fashion around the artery, extending from the area superficial to the artery to the area lateral to it. The approach to the brachial plexus is technically easier from the lateral position because of the presence of the patient’s neck.

After local anesthetic infiltration of the skin, the block needle is introduced along the long axis of the probe. It is essential not to insert the needle too deep, because the brachial plexus is a very superficial structure at this level. Once the needle tip is at the target, local anesthetic is injected. Adequate block can only be accomplished if the local anesthetic is deposited around the brachial plexus; therefore, several injections around the structure may be necessary to achieve this spread. Observation of the local anesthetic spread on the ultrasound image is very important for confirmation of a successful block.

Infraclavicular Block

In the second part of the subclavian artery, the nerve divisions reunite with each other to form nerve cords. Around the artery, the cords are arranged in a circumferential manner within the neurovascular sheath at medial, lateral, and posterior locations. Infraclavicular blocks are typically performed at the location slightly medial to the coracoid process.

Technical choices
Probe Selection: Curved Array
Frequency: 3-7 MHz
Needle Selection: 18 or 20 gauge 4-6” block needle

Technique: The patient is positioned supine with the head tilted slightly to the contralateral side. It is helpful to abduct the patient’s arm so visualization of structures is maximized. The ultrasound probe is then positioned sagitally to obtain a cross-sectional view of the subclavian vessels and nerves. Optimal view of the structures is typically attained at the location slightly medial to the coracoid process below the clavicle. At this location, three hyper-echoic structures should be seen around the subclavian/axillary artery, in a medial, lateral, and posterior arrangement. These are the brachial plexus cords.

After local anesthetic infiltration to the skin, the block needle is introduced along the long axis of the probe. The easiest approach to the brachial plexus is from the cephalad direction at a 45 degree angle. When approaching the neurovascular bundle, a “pop” through the block needle should be felt. The position of the needle is then confirmed by observing the pattern of local anesthetic spread around the subclavian/axillary artery when the injection is made. It is sometimes helpful to inject around the artery a few times to ensure optimal local anesthetic spread.

Axillary Block

As the brachial plexus continues to travel distally into the upper extremity, the cords send out branches to innervate areas of the shoulder and the upper arm. The nerve cords then become terminal nerve branches. While radial, ulnar, and median nerves still travel with the subclavian/axillary artery within the neurovascular sheath, the musculocutaneous nerve branches out of the lateral cord and travels within the coracobrachialis muscle. Axillary block is typically performed by injection around the axillary artery.

Technical choices
Probe Selection: Linear or Curved Array
Frequency: 7 MHz or higher
Needle Selection: 20 or 22 gauge 2” block needle

Technique: The patient is positioned supine with the head tilted slightly to the contralateral side and the shoulder abducted at 90 degrees. The ultrasound probe is then positioned in the axilla to obtain a cross-sectional view of the axillary vessels and nerves. At this level, the axillary artery and vein are positioned within the groove formed by the biceps muscle within the neurovascular sheath. Brachial plexus nerves appear as hyper-echoic round structures around the axillary artery. It was traditionally thought that each of the nerves is located in four quadrants around the artery. However, we now know that their locations are highly variable. Regardless of the exact position of the nerves, the aim of this block is to inject around the axillary artery within the neurovascular sheath, which provides a predictable result.

After local anesthetic infiltration of the skin, the block needle is introduced along the long axis of the probe. Once the needle is in position, local anesthetic is injected and its spread around the artery is visualized. It is sometimes necessary to inject several times around the artery to ensure an adequate block. Using the ultrasound allows for predictability without eliciting a paresthesia or traversing the axillary artery. In addition, the musculocutaneous nerve can be blocked by identifying the nerve within the substance of the coracobrachialis muscle and injecting around it.

Principles of Ultrasound Technology

The ultrasound device consists of two basic components: the transducer probe and the machine. First, high frequency sound waves are generated by the probe and are emitted from the tip. These ultrasonic waves typically have a frequency range of 1 to 15MHz, and thus are inaudible, as the upper limit of human hearing is approximately 20 kHz. The sound waves are then transmitted from one tissue to another, as some waves are reflected more superficially, while others travel on farther until they reach deeper tissue and then themselves get reflected back. The reflected waves are detected by the probe, and the information is relayed back to the ultrasound machine. The machine compiles the data, and displays the distances and intensities of the reflected waves on its screen, forming a two-dimensional image.

Different human structures have varying reflective properties which allow them to be visualized by using ultrasound technology. For example, bones have a very high reflective index and appear as dense (“hyper-echoic”) structures, while fat tissues with a low reflective index appear pale (“hypo-echoic”). As ultrasound wave frequency is increased, a higher resolution is seen, but with lower penetration. Conversely, lower frequency ultrasound waves have deeper penetration but with lower image resolution. Therefore, higher frequency ultrasound may be suitable for smaller and superficial structures, while lower frequency is preferred for larger and deeper structures.

Also, the shapes of the ultrasound probe may affect the image. A linear array probe emits ultrasound waves in a straight frontal direction, while a curved array probe emits waves in a fan-like fashion. The resulting images look different depending on the probe choice. The ultrasound operator must choose the correct probe type for each task.

References

[1] Perlas A, Chan VW, Simons M.: Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study. Anesthesiology. 2003 Aug;99(2):429-35.

[2] Fanelli G, Casati A, Garancini P, Torri G.: Nerve stimulator and multiple injection technique for upper and lower limb blockade: failure rate, patient acceptance, and neurologic complications. Study Group on Regional Anesthesia. Anesth Analg. 1999 Apr;88(4):847-52.

[3] La Grange P, Foster PA, Pretorius LK: Application of the Doppler ultrasound bloodflow detector in supraclavicular brachial plexus block. Br J Anaesth. 1978 Sep;50(9):965-7.

[4] Williams SR, Chouinard P, Arcand G, Harris P, Ruel M, Boudreault D, Girard F.: Ultrasound guidance speeds execution and improves the quality of supraclavicular block. Anesth Analg. 2003 Nov;97(5):1518-23

Clinical Window Web Journal #26: Ultrasound Guided Upper Extremity Nerve Blocks (December 2008). ISSN 1795-6269.

Acknowledgement: Thanks to the authors for their text and photos, and to the New York University School of Medicine for the opportunity to share this educational information with clinicians as global readers of Clinical Window. Special thanks to Prof. Charlotte Bell, MD for her collaboration and advice in the publishing process.

Published by permission of GASNet Inc. © 2005-6.

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Last updated: 30 December 2008
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