Interscalene Brachial Plexus Block

Fig. 19.1

Patient positioning and surface landmarks for interscalene brachial plexus block

19.2.1 Patient Positioning

The patient lies supine with the head rotated approximately 45° to the nonoperative side after general anesthesia has been induced. Surface landmarks include:

Clavicular head of the sternocleidomastoid muscle:
- The lateral border of the sternocleidomastoid muscle marks the location of the anterior scalene muscle. This portion of the sternocleidomastoid muscle can be accentuated by asking the child to reach in the direction of the ipsilateral knee before induction of general anesthesia.
Interscalene groove:
- The groove is located between the anterior and middle scalene muscles approximately 1 cm above the separation of the sternal and clavicular heads of the sternocleidomastoid muscle. The anterior scalene muscle lies immediately behind the lateral border of the clavicular head of the sternocleidomastoid muscle at the level of the cricoid cartilage (C6). The groove is made more pronounced by asking older children to raise the head or take a deep breath while awake.
Chassaignac’s tubercle:
- The anterior tubercle on the C6 vertebra is located at the intersection of the interscalene groove with the transverse plane of the cricoid cartilage. This landmark is more applicable in adolescents (whose vertebrae are better developed).

When using the interscalene approach, the point of needle insertion is at the level of C6 within the interscalene groove. For the parascalene approach, a line is drawn between the midpoint of the clavicle and the transverse process of C6. The needle insertion site is two-thirds of the way down this line, near the external jugular vein.

19.3 Nerve Stimulation Technique (Tables 14.1 and 19.1)

Table 19.1

Responses and recommended needle adjustments for use during nerve stimulation at the interscalene level

Correct response to nerve stimulation

Twitches elicited from the upper and middle trunks (pectoralis, deltoid, biceps brachii muscles) and middle and lower trunks (triceps, forearm or hand muscles) with current intensity of at least 0.4 mA (0.1–0.3 ms) verify stimulation of the brachial plexus

Other common responses and needle adjustments

Muscle twitch from electrical stimulation

Neck (anterior scalene or sternocleidomastoid)

Explanation: needle usually anteromedial to plexus

Needle adjustment: withdraw needle to subcutaneous tissue and reinsert in a 10–20° more posterior angle

Diaphragm (phrenic nerve)

Explanation: needle plane is too anterior

Needle adjustment: withdraw needle to subcutaneous tissue and reinsert in a 15° more posterior angle

Scapula (thoracodorsal nerve to serratus anterior muscle)

Explanation: needle tip is too posterior and deep to brachial plexus

Needle adjustment: withdraw to subcutaneous tissue and reinsert in a more anterior plane

Trapezius (accessory nerve)

Explanation: needle tip too posterior to plexus

Needle adjustment: withdraw to subcutaneous tissue and reinsert in a more anterior plane

Bone contact

Needle stops a depth of 1–2 cm (transverse process of cervical vertebrae or first rib), without twitches

Explanation: needle shaft angle is too posterior and touching anterior tubercles

Needle adjustment: withdraw to subcutaneous tissue and reinsert in a 15° more anterior angle

Vascular puncture

Most commonly carotid artery puncture; seen as arterial blood aspiration

Explanation: needle angle and tip anterior to plexus

Needle adjustment: withdraw completely for pressure treatment and reinsert tip 1–2 cm posterior

Alternative explanation: vertebral artery puncture. Especially a risk in OOP technique or when there is difficulty with needle tip visualization in either plane

Needle adjustment : needle tip is too medial, must be withdrawn and reinserted laterally

19.3.1 Needle Insertion

A flowchart illustrating the needle insertion site and procedures is shown in Fig. 19.2.

Fig. 19.2

Flowchart of needle insertion and procedures for an interscalene brachial plexus block

A 22G–25G, 30–35 mm (depending on the age and size of the child), short-beveled needle is inserted at an acute angle relative to the skin surface and directed medially, posteriorly, and caudally.
In children, the compact arrangement of anatomical structures within the neck may warrant a modified, angled needle insertion (as compared to the perpendicular orientation often used in adults) in order to prevent inadvertent puncture of the vertebral artery or epidural/subarachnoid space [1].

Clinical Pearl

Needle insertion below C6 has been described (including the parascalene approach described by Dalens et al. [2]); both approaches are successful.
For the parascalene approach, a line is drawn between the midpoint of the clavicle and the transverse process of C6 (Chassaignac’s tubercle). The needle is inserted perpendicular to the skin two-thirds of the way down this line near the external jugular vein.

19.3.2 Current Application and Appropriate Responses

Figure 19.3 illustrates the procedure for employing nerve stimulation techniques for interscalene brachial plexus block.

Fig. 19.3

Flowchart of procedure for employing nerve stimulation techniques for interscalene brachial plexus block

Applying an initial current of 0.8–1.0 mA (2 Hz, 0.1–0.3 msec) is sufficient for stimulation of the plexus.
After obtaining the appropriate motor response, the current is reduced to aim for a threshold current of 0.4 mA (0.1–0.2 msec).
Motor response cessation at currents less than 0.2 mA indicates the needle is probably intraneural.
Twitches elicited from the upper and middle trunks (pectoralis, deltoid, biceps brachii muscles) and lower trunks (triceps, forearm, and hand muscles) verify stimulation of the brachial plexus.

19.3.3 Modifications to Inappropriate Responses

An algorithm of modifications to inappropriate responses to nerve stimulation is shown in Fig. 19.4.

Fig. 19.4

Flowchart of modifications to inappropriate responses to nerve stimulation during interscalene block

19.4 Ultrasound-Guided Technique

For a summary of ultrasound-guided interscalene block techniques, see Fig. 19.5. Major anatomical structures in the brachial plexus as captured by MRI and VHVS images are shown with the corresponding ultrasound image in Fig. 19.6.

Fig. 19.5

Flowchart of ultrasound-guided techniques in interscalene blocks

Fig. 19.6

(a) VHVS and MRI images of anatomical structures in the brachial plexus. (b) Ultrasound image of the brachial plexus at the interscalene groove

The roots of the plexus are clearly visible in the ultrasound image with corresponding cadaveric and MRI images. Table 19.2 summarizes particular imaging considerations in pediatric populations. Patient positioning and anatomical landmarks are the same for ultrasound techniques as they are for landmark and nerve stimulation techniques. If nerve stimulation is employed in conjunction with ultrasound imaging, the previous section can be referred to for appropriate responses and modifications.

Table 19.2

Anatomical and imaging considerations for interscalene block

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