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Ultrasound Guided Nerve Block

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Illustration 1: Course of the Brachial Plexus.

Illustration 2: Common distribution of anesthesia, infraclavicular block.

Figure 1: Probe placement in the infraclavicular fossa.

Figure 2:  Ultrasound image of the infraclavicular fossa.

Figure 3:  In-plane needle placement for the infraclavicular block.

Video 1:  Infraclavicular block

 


Leonard V. Bunting, M.D.

Infraclavicular Brachial Plexus Block

Introduction
The infraclavicular brachial plexus block provides dense anesthesia in the same regions as the supraclavicular block (upper arm, elbow, forearm and hand). However, it avoids the risk of phrenic nerve block, making it an excellent choice in those patients with respiratory issues. Additionally, as the choice of “in-plane” approach (arm is abducted) vs. “out-of-plane” approach (arm in neutral position) make patient positioning less critical, it should be considered in patients with arm injuries that limits their movement.  In one study, the infraclavicular approach was found to have faster onset, denser anesthesia and fewer complications compared to the supraclavicular approach. (1)


Anatomy
The brachial plexus exits the interscalene space and turns laterally to run on the supero-lateral aspect of the subclavian artery. The plexus travels with the subclavian artery as it exits the supraclavicular fossa behind the clavicle and then passes over the first rib to become the axillary artery. In the infraclavicular fossa, the brachial plexus separates into individual cords that are appropriately named medial, lateral and posterior based on their locations relative to the axillary artery. These cords bundle around the axillary artery as it travels inferior to the coracoid and into the axilla. In the infraclavicular fossa, the bundle lies 4-6 centimeters under the skin, superficial to the lung and deep the pectoralis muscles. The axillary vein runs inferior to the artery (Illustration 1 and 2).   Often, the infraclavicular region contains a significant amount of connective tissue with septations.



Illustration 1: Course of the Brachial Plexus.

Illustration 2: Common distribution of anesthesia, infraclavicular block.


Scanning Technique
The patient may be positioned anywhere from recumbent to sitting. Although the block can be managed with the arm in any position, abduction of the arm has been shown to bring the artery and plexus closer to the skin.(2)  This reduction in depth is expected to improve visualization of the target nerves and could improve visualization of the block needle by decreasing its angle relative to the probe. Given the deep placement, lower frequency probes may be necessary (4-8 mHz) and a curved array probe can be used if visualization is limited by depth.  In general, however, a high-frequency linear probe is preferred. The transducer is placed just medial to the coracoid process with its cranial end just below the clavicle.

The orientation of the probe is parallel to an imaginary line that connects the AC joint and the ipsilateral nipple (Figure 1).
In this position, the pectoralis major and minor muscles can be identified just above the brachial vessels and plexus. The artery lies cranial in this view and becomes the axillary artery emerging from beneath the clavicle. It is identified by its thick wall and brisk pulsations. The axillary vein lies caudal running infero-medial from the artery and is compressible. The vessels traverse the infraclavicular fossa before running under the choracoid process. The probe is rotated as needed to obtain a transverse image of the artery. 

The three cords of the brachial plexus appear as hyperechoic circles that surround the axillary artery. The lateral cord lies closest to the coracoid. Proceeding around the artery, the posterior cord is deep to the artery and the medial cord lies furthest from the coracoid, sometimes between the artery and vein.  Given the deep lie of the cords, these relationships may not be apparent until the cords are surrounded by local anesthetic.

 


Figure 1:  Probe placement in the infraclavicular fossa.

Figure 2:  Ultrasound image of the infraclavicular fossa.  The axillary artery “A” (red),
axillary vein “V” (blue), and lateral “L”, medial “M” and posterior “P” cords
(yellow) are located superior to the intercostal muscles and pleura.

Nerve Block
The needle can be inserted using the “in-plane” approach (In-Plane vs. Out-Of Plane Approach) from superior or inferior of the transducer, or one can utilize an “out-of plane” technique. The goal of the infraclavicular block is to surround each cord with local anesthetic. This can be challenging given the deep lie of the cords and the potential significant amount of connective tissue and septations occuring in this anatomical region. A simplified yet reliable approach aims at surrounding the axillary artery with local anesthetic. (3)

Figure 3:  In-plane needle placement for the infraclavicular block.


After the appropriate equipment is setup (POPUP – anesthetic, needle and sterile), the skin is anesthetized and the block needle is inserted 1 cm into the skin. The needle tip is sonographically located and followed throughout the procedure (POPUP – visualizing the tip). This can be difficult as the angle of the needle is often steep.  Being careful to avoid any sensitive structures, the needle is slowly advanced towards the deep border of the artery.  Injecting small amounts of solution during needle insertion can be helpful verifying needle tip location. (POPUP-Block Precautions)  Once the needle is in the vicinity of the artery, anesthetic is injected.  Often, a U-shaped spread of anesthetic around the axillary artery can be produced with an injection posterolateral from the artery. This has been associated with rapid onset of a complete block. (4)  Another frequent observation is that a block has a high success rate when a fascial “click” can be felt during injection posterior to the artery.  This has also been linked with a rapid distribution of anesthetic around the artery. (5)
Appropriate needle placement is confirmed by spread of anesthetic around the artery, dissecting the cords away from the artery, often giving the appearance that the cords move “towards” the needle (Video 1).  Typical block volumes are 20-30cc’s.

Video 1:  Infraclavicular block. 

The needle is poorly visualized due to its steep angle. It courses from the upper right as seen by the tissue movement. The tip is visualized deep to the artery once the anesthetic fills the space. Spread of local anesthetic is seen around the deep border of the artery. Complete anesthesia was obtained in 5-7 minutes.

Pearls and Pitfalls
The steep angle of the needle for this block can severely limit needle visualization. Applying extra pressure to the side of the probe furthest from the needle will tilt the ultrasound beam towards the needle, effectively reducing the probe angle. This may aid in visualization.

Needle visualization is greatly improved once it is surrounded by anechoic fluid. Therefore, injecting small amounts of solution during needle insertion can greatly improve its visualization and guidance.
Although ultrasound guidance provides excellent understanding of needle placement, intravascular injection can still occur. (6)  Any injection that does not lead to an identifiable anechoic bolus should raise concern. Careful aspiration and incremental injection is paramount to avoid systemic toxicity.

Although one large case series of infraclavicular blocks reported no pneumothoraces (7), individual cases have been published. (8)  However, the lung lies quite deep in this region, so careful needle control should prevent this complication.

References

1. Koscielniak-Nielsen ZJ, Frederiksen BS, Rasmussen H, Hesselbjerg L.
A comparison of ultrasound-guided supraclavicular and infraclavicular blocks for upper extremity surgery. Acta Anaesthesiol Scand, 2009;53:620-626.

2.  Ruíz A, Sala X, Bargalló X, Hurtado P, Arguis MJ, Carrera A.
The Influence of Arm Abduction on the Anatomic Relations of Infraclavicular Brachial Plexus: An Ultrasound Study. Anesth Analg, 2009;108(1):364-366.

3.  Gray A.
Ultrasound Guidance for Regional Anesthesia. In: Miller R. (ed): Miller: Miller’s Anesthesia, 7th edition. Churchill Livingstone, 2009; Chapter 53: 18.

4. Dingemans E, Williams SR, Arcand G, Chouinard P, Harris P, Ruel M, Girard F.
Neurostimulation in ultrasound-guided infraclavicular block: a prospective randomized trial. Anesth Analg, 2007;104:1275-80.

5. Levesque S, Dion N, Desgagne MC.
Endpoint for successful, ultrasound-guided infraclavicular brachial plexus block. Can J Anaesth,2008;55(5):308.

6.  Martínez Navas A, DE LA Tabla González RO.
Ultrasound-guided technique allowed early detection of intravascular injection during an infraclavicular brachial plexus block. Acta Anaesthesiol Scand. 2009;53(7):968-70.

7.  Sandhu NS, Manne JS, Medabalmi PK, Capan LM.
Sonographically guided infraclavicular brachial plexus block in adults: a retrospective analysis of 1146 cases. J Ultrasound Med, 2006;25(12):1555-61.

8.  Koscielniak-Nielsen ZJ, Rasmussen H, Hesselbjerg L.
Pneumothorax after an ultrasound-guided lateral sagittal infraclavicular block. Acta Anaesthesiol Scand. 2008;52(8):1176-7.


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