Interscalene Brachial Plexus Block


The interscalene technique is ideal for coverage of the lateral 2/3 of the clavicle (clavicular surgery will often be incomplete, as there is joint innervation by the cervical plexus), the shoulder, and the proximal humerus(note that when arthroscopic surgery is undertaken, the posterior arthroscopic port may require additional infiltration). Because the inferior trunk (C8-T1) is often inadequately blocked, it may require supplementation in the ulnar distribution if used for arm or forearm surgery. The interscalene technique traditionally has NOT reliably blocked the hand, thus more distal blocks should be considered. With ultrasound-guided techniques, the adequate hand blockade should be achievable, provided that an attempt is made to ensure blockade of the lower trunk

One advantage of the interscalene block over the supraclavicular is that it blocks part of the cervical plexus. That said, the cervical plexus can be easily blocked with a field block along the posterior border of the sternocleidomastoid

Relevant Anatomy

Landmarks and Surrounding Structures

Important landmarks include the anterior and middle scalene muscles and the subclavian artery. It is important to note that the pleura lies anteromedial to the inferior trunk.

Brachial Plexus Anatomy

The brachial plexus is thought to consist of C5-T1, although it may expand by one nerve in either direction (C4-T2). Essential to the anesthesiologist is an understanding of the trunks – upper, middle, and lower

Upper (C5-C6)
Middle (C7)
Lower (C8-T1)

Cutaneous Innervation

Superior lateral cutaneous nerve (continuation of the posterior cord of the axillary nerve, which derives from all three trunks). Innervates lateral shoulder and skin over the deltoid

Medial brachial cutaneous nerve (C8-T1, arises from the medial cord of the brachial plexus): upper medial arm

Intercostobracheal nerve (T2, cutaneous branch of an intercostal nerve, innervates the upper medial arm, and potentially part of the shoulder. Must be supplemented if a brachial plexus block is used

Joint Innervation

The shoulder joint itself is innervated by the:

Axillary (C5-C6, all trunks)
Suprascapular (C4-C6, upper trunk or C5 root)
Subscapular nerves (C5-C6, middle cord), and sometimes the
Musculocutaneous nerve (C5-C7, its contribution varies widely)

Thus, if C5-C7 are anesthetized, the shoulder joint itself should be completely anesthetized

Distributions Missed by the Interscalene Technique

Posterior arthroscopic port: may require additional infiltration

Cephalad cutaneous shoulder (above the clavicle): innervated by the supraclavicular nerves (from the lower cervical plexus, i.e. C3-C4). In order to assure complete analgesia for arthroscopic shoulder surgery, the supraclavicular nerves must be blocked

Inferior trunk: often inadequately blocked


Posterior arthroscopic port: local infiltration
Supraclavicular nerves:


External landmarks include the clavical, interscalene groove, and lateral border of the clavicular SCM. Scan the entire area, taking care to visualize the great vessels, SCM, and scalene muscles. Scan caudally, until the brachial plexus comes into view between the scalene muscles. If difficult to locate, consider going straight to the supraclavicular approach and then scanning upwards (“trace back method”)


An ipsilateral phrenic nerve block occurs in almost 100% [Urmey WF et al. Anesth Analg 72: 498, 1991] and leads to a 25% reduction in pulmonary function [Urmey WF et al. Anesth Analg 74: 352, 1992; Fujimura N et al. Anesth Analg 81: 962, 1995] – this procedure is therefore contraindicated in anyone with respiratory insufficiency or a contralateral nerve palsy. Risk of pneumothorax is remote but real. Recurrent laryngeal nerve is occasionally blocked as well, and this can lead to hoarseness and complete airway obstruction in patients with an existing vocal cord palsy (thus ask about hoarseness or previous neck surgery). Slight caudad direction of the needle reduces the risk of accidental epidural, subarachnoid, or vertebral artery injection. Meticulous aspiration is a requirement. As with all peripheral nerve blocks, permanent neurologic injury is possible, but rare

The Bezold-Jarisch reflex results in unmyelinated vagal afferent stimulation in response to noxious ventricular stimuli (chemical or mechanical), leading to the triad of hypotension, bradycardia, and coronary vasodilation (mediated via increased parasympathetic tone as well as by ANP and BNP). In the setting of shoulder surgery, it is postulated that the combination of increased levels of circulating epinephrine combined with the sitting position may irritate the left ventricle, leading to the massive parasympathetic outflow that accompanies the Bezold-Jarisch reflex [D’Alessio JG et al. Activation of the Bezold-Jarisch reflex in the sitting position for shoulder arthroscopy using interscalene block. Anesth Analg 80: 1158, 1995; FREE Full-text at Anesthesia & Analgesia]. It is also thought that perioperative beta blockade may increase the incidence of this dangerous reflex [D’Alessio JG et al. Activation of the Bezold-Jarisch reflex in the sitting position for shoulder arthroscopy using interscalene block. Anesth Analg 80: 1158, 1995; FREE Full-text at Anesthesia & Analgesia]. The Bezold-Jarish reflex (bradycardia and hypotension following sudden loss of cardiac stimulation) occurs in 15-30% of patients and can be treated by volume, atropine, and ephedrine

Interscalene Block: Side Effects

  • Diaphragmatic hemiparesis from ipsilateral femoral block (100% incidence, 25% reduction in pulmonary function)
  • Pneumothorax
  • Permanent neurologic injury
  • Blockade of vagus, recurrent laryngeal, and cervical sympathetic nerves (Horner’s syndrome)
  • Epidural or subarachnoid injection
  • Vertebral artery injection
  • Severe hypotension and bradycardia (Bezold-Jarisch reflex)

Analysis of the Closed Claims Database suggests that nerve damage is the cause of 16% of claims, with 78% of these occurring under general anesthesia and 22% occurring after regional anesthesia. The ulnar nerve is most commonly injured (28%), followed by the brachial plexus (20%). Keep in mind, however, that Closed Claims Data lacks a denominator [Kroll DA et al. Anesthesiology 73: 202, 1990]

See Also

Ultrasound for Regional Anesthesia NYSORA