Scanning Technique

• Position the patient supine with the head turned 45 degrees to the contralateral side.
• After skin and transducer preparation (see Preparing Transducer for Single Shot), place a linear 38-mm, high frequency 10-15 MHz transducer firmly on the neck at the level of the cricoid cartilage in the axial, oblique plane to obtain the best possible transverse view of the brachial plexus.

Transducer over left interscalene region CL = clavicle

• Optimize machine imaging capability by selecting the appropriate depth of field (within 2-3 cm), focus range and gain.
• Visualize the nerve roots or trunks in the transverse view (short axis). Nerves in the interscalene groove appear hypoechoic, distinctly round or oval, and are located between the anterior and middle scalene muscles. The internal jugular vein and carotid artery are visualized medially.

Anatomical Correlation

Arrows indicate beam direction Arrowheads = nerve roots ASM = anterior scalene muscle CA = carotid artery IJV = internal jugular vein MSM = middle scalene muscle SCM = sternocleidomastoid muscle White box = imaged region

Nerve Localization

• Perform a systematic anatomical survey from medial to lateral and superficial to deep.
• The great vessels (carotid artery and internal jugular vein) serve as an easily identifiable point of reference.
• Medial to the great vessels, identify the thyroid gland and the trachea.
• Superficial to the great vessels is the triangular shaped sternocleidomastoid muscle.

CA = carotid artery

SCM = sternocleidomastoid muscle

• Lateral to the carotid is usually the internal jugular vein.

IJV = internal jugular vein CA = carotid artery SCM = sternocleidomastoid muscle

• Lateral to the great vessels is the anterior scalene muscle.
• The brachial plexus is visualized in the interscalene groove between the anterior and middle scalene muscles.
• Bring the roots/trunks into view by tilting/angling the transducer so that the beam is 900 to the nerves.

ASM = anterior scalene muscle Arrowhead = nerve root MSM = middle scalene muscle SCM = sternocleidomastoid muscle

• Follow the nerves cephalad by moving the transducer to the upper interscalene region.

Upper Interscalene Region (above C6) ASM = anterior scalene muscle Arrowhead = nerve root SCM = sternocleidomastoid muscle TP = transverse process

• Visualize the cervical nerve root (arrowhead) as it emerges from the neural foramen next to the transverse process (TP) (see figure above).
• The anterior scalene muscle is small in the upper interscalene location.

Mid Level Interscalene Region (C6 level) ASM = anterior scalene muscle Arrowhead = nerve root SCM = sternocleidomastoid muscle

• The ASM is now larger in size at this level and more nerve roots are seen in the interscalene groove (see figure above).

Lower Interscalene Region (Below C6) ASM = anterior scalene muscle Arrowhead = nerve root SCM = sternocleidomastoid muscle VA = vertebral artery

• Move the transducer caudad to visualize branching of nerve roots (arrowheads) into trunks which travel superficially towards the skin surface (see figure above).
• The vertebral artery (VA) usually becomes visible below the C6 transverse process.

Needle Insertion Approach

In Plane Approach (Lateral to Medial)

• Ultrasound guided interscalene block is considered a BASIC skill level block because this is a superficial block.
• For the in plane approach, insert a 5 cm 22G insulated block needle on the outer (lateral) end of the ultrasound transducer after skin local anesthetic infiltration. Advance the needle along the long axis of the transducer in the same plane as the ultrasound beam. This way, the needle shaft and tip can be visualized in real time as the needle is advanced towards the target nerves.

• Confirm the identity of the nerves by electrical stimulation if desired. Useful endpoints for shoulder surgery are deltoid or biceps muscle contraction for the interscalene block.

In Plane Approach - Needle in the Interscalene Groove

ASM = anterior scalene muscle Arrows = block needle Arrowheads = nerves MSM = middle scalene

---

Out of Plane Approach

• The OOP approach is another common approach for interscalene block and for interscalene catheter placement.
• For the OOP approach, align the target nerve with the midpoint of the transducer and then insert the block needle.

• Observe tissue and needle movement as the needle is advanced towards the target.
  
• Clear identification of the needle tip can be technically challenging.
• It is advantageous to inject a small volume of local anesthetic (1 mL) during needle advancement to facilitate tracking of the needle tip (see Needle Localization).
• Needle to nerve contact can be confirmed by electrical stimulation (if desired) and local anesthetic spread around the nerves.

The Effect of Head Turning

SCM = sternocleidomastoid muscle

• In figure A, the sternocleidomastoid (SCM) muscle is noted to be overlying the interscalene groove (arrow = lateral end of SCM muscle) during OOP approach. Head rotation farther to the contralateral side will move the SCM muscle out of the needle path (as seen in figure B). The lateral end of the SCM muscle (arrow) is now medial to the interscalene groove (white dotted line).

Local Anesthetic Injection

• Observe the pattern of local anesthetic spread around the target nerves in real time during injection.
• Local anesthetic is seen as a hypoechoic fluid collection between the two scalene muscles.
• The usual volume of local anesthetic administration is between 15 (for analgesia only) and 40 mL (for surgical anesthesia).

ASM = anterior scalene muscle Arrows = block needle Arrowheads = nerves LA = local anesthetic MSM = middle scalene

• Avoid intramuscular injection which is indicated by an increase in echogenicity within the muscle bulk.
• Adjust the needle position during injection to optimize local anesthetic spread if necessary.
• Scan proximal and distal to assess the extent of local anesthetic spread.

Post Injection Nerves have a hyperechoic outline after injection and are clearly visualized. Arrowheads = nerves

• It is important to avoid local anesthetic injection immediately adjacent to the transverse process and the nerve root emerging from the neural foramen because of the risk of unintentional epidural or spinal anesthesia.

Recommendations: DO NOT inject at location # 1 since it is immediately next to the TP; injection at locations 2 and 3 is more appropriate. Arrowheads = nerves TP = transverse process

Clinical Pearls - Nerve Localization

1. The Trace Back Method

If the nerve roots in the interscalene region are difficult to visualize, scan inferiorly in the supraclavicular region to identify the trunks/divisions of the brachial plexus (often seen as "a bunch of grapes"). Next move the transducer cephalad to trace the nerve roots more proximally in the interscalene region.

Arrowheads = nerves

SA = subclavian artery

Arrowheads = nerves

SA = subclavian artery

ASM = anterior scalene muscle	Arrowheads = nerves	MSM = middle scalene muscle
SA = subclavian artery

ASM = anterior scalene muscle	Arrowheads = nerves	MSM = middle scalene muscle
SA = subclavian artery

2. Identifying a Specific Nerve Root

One way to more accurately identify the nerve root and its corresponding level is to examine the shape of the transverse processes. The transverse processes at and above C6 cast a bony shadow that is shaped like a "U", representing the anterior and posterior tubercles. Also, the vertebral artery is generally visualized below C6.

	Sonogram showing C5 nerve root entering the neural foramen Note the U shaped transverse process (TP) showing prominent anterior and posterior tubercles at C5.
	Sonogram showing C6 nerve root entering the neural foramen Note the U shaped transverse process (TP) showing prominent anterior and posterior tubercles at C6.
	Sonogram showing C7 nerve root entering the neural foramen Note the transverse process (TP) is less prominent (without an anterior tubercle at C7).

The vertebral artery is usually visualized below C6.

3. The Phrenic Nerve

• Because the phrenic nerve is commonly affected during interscalene block, it may be worthwhile to identify the phrenic nerve and inject local anesthetic at a distance far away from the phrenic nerve.
• However, the small phrenic nerve (1-1.5 mm) often lies in a narrow plane between the sternocleidomastoid and anterior scalene muscles (Pictures: courtesy of Dr. Andre Ceccoli, France). Its identity can be confirmed by nerve stimulation.
• Color Doppler may be necessary to differentiate small hypoechoic vessels e.g., branches of the transverse cervical artery from the hypoechoic phrenic nerve, both lying in the same intermuscular plane.

	The small hypoechoic structure in the plane between the sternocleidomastoid muscle (SCM) and the anterior scalene muscle (ASM) is suspected to be the phrenic nerve (arrowhead). MSM = middle scalene muscle
	To confirm its identity, a needle (arrows) is inserted in a medial to lateral direction to enter the intermuscular plane and approach the hypoechoic structure (arrowhead). ASM = anterior scalene muscle MSM = middle scalene muscle SCM = sternocleidomastoid muscle
	A small amount of fluid (indicated by the asterisk) is injected to "hydro dissect" and open up the plane. This allows clearer visualization of the small hypoechoic structure (arrowhead). ASM = anterior scalene muscle MSM = middle scalene muscle SCM = sternocleidomastoid muscle

Catheter Insertion

• Continuous interscalene block (CISB) is indicated for shoulder analgesia and can be achieved by local anesthetic infusion through a catheter placed in the interscalene groove (see Catheter Technique).
• The out of plane needle approach is generally recommended for CISB with the needle inserted high up in the neck (C4-5 level). Distal needle insertion and catheter advancement may result in distal anesthesia in the hand without adequate shoulder analgesia.
• Injection of local anesthetic or D5W solution (if nerve stimulation is desired) through the needle to distend the interscalene groove is recommended to facilitate the ease of catheter advancement.
• Local anesthetic spread can be observed in real time during catheter injection.

	A. A nerve root (arrowheads) in the proximal interscalene groove.
	B. Fluid injection through the block needle (arrow) to distend the interscalene groove prior to catheter insertion
	C. Local anesthetic (LA) spread in the proximal interscalene groove after catheter injection; the hyperechoic dot = catheter
	D. Local anesthetic (LA) spread in the distal interscalene groove after catheter injection; the hyperechoic dots = transverse view of a coiled catheter

Image Gallery

1. A Parasagittal Scan To Visualize Nerve Roots Emerging From The Neural Foramina

	A longitudinal scan with the transducer positioned parallel to the trachea on the left side of the neck This can be a useful technique to locate higher cervical nerve roots (above C5).
	A transverse view of the brachial plexus in the parasagittal plane Arrowheads = nerve roots NF = neural foramen SCM = sternocleidomastoid muscle

2. Vertebral Artery in The Lower Interscalene Groove Below C6

	ASM = anterior scalene muscle muscle SCM = sternocleidomastoid muscle
	The vertebral artery (VA) is visualized usually when the transducer is scanning below C6 because the artery is housed within the foramina of the C1-C6 transverse processes.

3. Aberrant Nerve Root

	A. A nerve root (between 2 arrowheads) is visualized between the sternocleidomastoid muscle (SCM) and the anterior scalene muscle (ASM) in the proximal interscalene region.
	B. The same nerve root has now moved towards the interscalene groove (dashed line) as the transducer is moved caudally. ASM = anterior scalene muscle muscle SCM = sternocleidomastoid muscle

Pictures: courtesy of Dr. Andre Ceccoli, France.

Video Gallery

Selected References

• Jan VG, Tielens L, Gielen M: Ultrasound-guided interscalene brachial plexus block in a child with femur fibula ulna syndrome. Paediatr Anaesth 2006; 16: 330-2.
• Chan VW: Applying ultrasound imaging to interscalene brachial plexus block. Reg Anesth Pain Med 2003; 28: 340-3.
• Perlas A, Chan VW, Simons M: Brachial plexus examination and localization using ultrasound and electrical stimulation: a volunteer study. Anesthesiology 2003; 99: 429-35.
• Demondion X, Herbinet P, Boutry N, Fontaine C, Francke JP, Cotten A: Sonographic mapping of the normal brachial plexus. Am J Neuroradiol. 2003; 24: 1303-9.
• Martinoli C, Bianchi S, Santacroce E, Pugliese F, Graif M, Derchi LE: Brachial plexus sonography: a technique for assessing the root level. Am J Roentgenol 2002; 179: 699-702.
• Sheppard DG, Iyer RB, Fenstermacher MJ: Brachial plexus: demonstration at US. Radiology 1998; 208: 402-6.
• Yang WT, Chui PT, Metreweli C: Anatomy of the normal brachial plexus revealed by sonography and the role of sonographic guidance in anesthesia of the brachial plexus. Am J Roentgenol 1998; 171: 1631-6.