**7. Interscalenic approach to the brachial plexus**

In blocking the brachial plexus in the proximal interscalene space, the anesthesia is applied to the roots or nerve trunks to achieve a metameric distribution of the anesthesia. The plexus is formed by the anterior divisions of the C5 to T1 nerves, with regular contributions from C4 and T2. When the nerve roots exit through the intervertebral foramina, they head down towards the first rib surrounded by a fascia or aponeurotic sheath. This sheath extends into the upper arm by forming partitions, which hinders the diffusion of the anesthetic. Just before you reach the first rib (interscalene space), the roots above are fused together to give three trunks, referred to as the superior (C5-C6), middle (C7) and lower (C8-T1) in a craniocaudal direction. Both the plexus and the scalene muscles are located within a limited anatomical region defined by the outer edge of the sternocleidomastoid muscle, the upper edge of the middle third clavicular and anterior border of the trapezius muscle. This area is located external to the jugular vein, which must be born in mind to avoid puncture.

In the interscalene groove, roots that form the brachial plexus begin to coalesce to give rise to the upper, middle and bottom trunk. At this site, the brachial plexus is located at an approximate distance of about 1 cm from the skin and therefore, it is advisable to use highfrequency (10-15 MHz) and low penetration (3 - 4 cm) probes for exploration.

### **8. Classic cross-cutting approach**

To perform the block, the patient is placed in a supine position with the head rotated slightly to the side contralateral to the blockade. In the classical approach we use a probe situated transversely direction, putting it in the midline of the neck and starting at the level of the cricoid cartilage (Figure 4).

Fig. 3. Schematic representation of the sensitive area of the intercostobrachialis nerve.

In blocking the brachial plexus in the proximal interscalene space, the anesthesia is applied to the roots or nerve trunks to achieve a metameric distribution of the anesthesia. The plexus is formed by the anterior divisions of the C5 to T1 nerves, with regular contributions from C4 and T2. When the nerve roots exit through the intervertebral foramina, they head down towards the first rib surrounded by a fascia or aponeurotic sheath. This sheath extends into the upper arm by forming partitions, which hinders the diffusion of the anesthetic. Just before you reach the first rib (interscalene space), the roots above are fused together to give three trunks, referred to as the superior (C5-C6), middle (C7) and lower (C8-T1) in a craniocaudal direction. Both the plexus and the scalene muscles are located within a limited anatomical region defined by the outer edge of the sternocleidomastoid muscle, the upper edge of the middle third clavicular and anterior border of the trapezius muscle. This area is located external to the jugular vein, which

In the interscalene groove, roots that form the brachial plexus begin to coalesce to give rise to the upper, middle and bottom trunk. At this site, the brachial plexus is located at an approximate distance of about 1 cm from the skin and therefore, it is advisable to use high-

To perform the block, the patient is placed in a supine position with the head rotated slightly to the side contralateral to the blockade. In the classical approach we use a probe situated transversely direction, putting it in the midline of the neck and starting at the level

frequency (10-15 MHz) and low penetration (3 - 4 cm) probes for exploration.

**7. Interscalenic approach to the brachial plexus** 

must be born in mind to avoid puncture.

**8. Classic cross-cutting approach** 

of the cricoid cartilage (Figure 4).

Fig. 4. A. Representation of the most relevant references in the neck skin to the perform an interscalene block. B. Material for blockade by neurostimulation. C. Plexus Neurolocalization by ultrasound. D. Plexus approach using ultrasound with needle insertion "flat" from the side.

In the resulting image and for educational purposes, three areas can be identified when using this approach. A superficial area (located in the upper area of the ultrasound screen) occupied mainly by muscle structures, most of them more shallow than the sternocleidomastoid muscle. A middle zone located immediately under the muscle plane described above in which the tracheal lumen and cricoid cartilage lie, and lateral to the tracheal lumen the homogeneous texture of the thyroid lobe can be observed (Figure 5a), together with two vascular structures: a) the most inner and rounded one going up to the pulsating carotid artery; and b) the outer triangular one that readily collapses on applying pressure with the scanning probe corresponds to the internal jugular vein (Figure 5b). A deep zone (located in the lower area of the ultrasound screen) the lower limit of which marks the vertebral transverse process, which at this level corresponds to C6. Once these structures have been identified, the probe can be moved laterally and by maintaining the same angle, interscalene scan plane is reached (Figure 5c).

Anesthesia for Arthroscopic Shoulder Surgery 59

In an alternative approach described by Jack Vander Beek, the ultrasound scan is performed in the caudocraneal sense instead of the medio-lateral sweep of the "classic" technique. This approach is especially useful in patients with previous anatomical changes in the neck (surgery, radiotherapy, lean muscle bellies, etc.). Whichever approach is chosen, it is advisable to make subtle and rapid caudocraneal movements that will help visualize the

Having identified the brachial plexus in the interscalene space, the needle is inserted lateral to the transducer (flat) and with a local anesthetic bolus (remember the plexus is located about 1 cm from the skin), the needle is advanced while directly visualization the plane with the transducer until it enters the interscalene groove and is located adjacent to a nerve root. It is preferable to situate the needle at the deepest roots so that when we start to infuse the local anesthetic, it pushes us toward superficial plexus, improving the success rate. After gentle aspiration, we proceed to inject the local anesthetic, confirming the spread of local

In cases of long-term surgery or intention analgesia, it may be appropriate to implant a

 Perimedulla Dissemination: which would produce a spinal block and require ventilation support. This can be prevented by aspiration prior to injection and checking

Systemic toxicity: direct intravascular injection (perform test prior to aspiration) or by

 Vasovagal syncope: due to a Bezold-Jarisch reaction (hypotension and bradycardia, possibly with extreme apnea). Cervical sympathetic blockage occurs and venous return becomes difficult due to the surgical position (sitting). It usually occurs 30-60 min after

 Changes in phonation, hoarseness if recurrent involvement (rare), superior laryngeal nerve block anesthesia of hemipharynx (more common). If phonation disturbance

Horner's syndrome: produced by affecting the stellate ganglion. If it persists, suspect

blockade. Treat with ephedrine or atropine if needed, and vascular fluid filling. Ipsilateral phrenic nerve palsy: is constant in the interscalene block. Translate a cephalic

persists, consider anatomical nerve involvement and monitoring.

anatomical node involvement such as hematoma.

Delayed neurological dysfunction: usually transient.

nerve roots. It is advisable to define the scalene and focus on finding the nerves.

**9. "Alternative" cross-cutting approach** 

**10. Implementation of the blockade** 

**11. Indications** 

catheter.

**12. Complications** 

there is no CSF fluid.

spread over C6.

Pneumothorax.

absorption of the anesthetic.

anesthetic into the interscalene groove by direct visualisation.

Primarily for analgesia and anesthesia of shoulder and proximal arm.

Fig. 5. Cervical screening ultrasound images left of the cricoid cartilage (C6), from medial to lateral. Figure 5b, the interscalene space can be seen just after the deposit of the local anesthetic (area designated).

Medium zone. Beneath the sternocleidomastoid muscle, the anterior scalene (located more medially) and middle scalene (located more laterally) muscles can be seen, and between the two muscles the roots of interscalene brachial plexus groove are located. Their images appear as oval or round, hypoechoic (dark image), hyperechoic rim (white) and often with a dot inside (Figure 5c).

Inferior zone. Located immediately under the scalene muscles, the longus colli can be identified lateral to the vertebral artery a round, hypoechoic and pulsating image crossing medially to laterally. It is important to differentiate the nervous structures (well rounded and hypoechoic but not pulsating) that are often in line but below them in the picture. If in doubt, the scan mode used color Doppler to show the pulsatile flow of the artery, which is not seen if the nerve roots are being explored.

Fig. 5. Cervical screening ultrasound images left of the cricoid cartilage (C6), from medial to lateral. Figure 5b, the interscalene space can be seen just after the deposit of the local

Medium zone. Beneath the sternocleidomastoid muscle, the anterior scalene (located more medially) and middle scalene (located more laterally) muscles can be seen, and between the two muscles the roots of interscalene brachial plexus groove are located. Their images appear as oval or round, hypoechoic (dark image), hyperechoic rim (white) and often with a

Inferior zone. Located immediately under the scalene muscles, the longus colli can be identified lateral to the vertebral artery a round, hypoechoic and pulsating image crossing medially to laterally. It is important to differentiate the nervous structures (well rounded and hypoechoic but not pulsating) that are often in line but below them in the picture. If in doubt, the scan mode used color Doppler to show the pulsatile flow of the artery, which is

anesthetic (area designated).

not seen if the nerve roots are being explored.

dot inside (Figure 5c).
