The ultrasound-guided interscalene brachial plexus block provides regional anesthesia to the entire upper extremity including the shoulder. Anesthesiologists routinely utilize the interscalene brachial plexus block during orthopedic surgery to provide anesthesia to the lateral clavicle, acromioclavicular joint, proximal humerus, and elbow. In the emergency department, current indications for the interscalene block include pain control for upper-extremity fractures (proximal humerus, midshaft humerus, etc.) and to facilitate manipulations and reductions of upper-extremity injuries. Also, the interscalene brachial plexus block may be an ideal alternative in the setting of large abscess incision and drainage, deep wound exploration, and complex laceration repair when procedural sedation is not feasible.
Although the interscalene approach has a lower risk of iatrogenic pneumothorax than the supraclavicular approach secondary to the higher approach on the neck, it is more likely to cause phrenic nerve paralysis due to tracking of local anesthetic around the anterior scalene muscle. Traditional high volumes injections of local anesthetic (greater than 30 mL) will reliably affect the phrenic nerve and cause paralysis of the ipsilateral hemidiaphragm for the duration of the block.4 While clinically insignificant in healthy patients, the risk of phrenic nerve paralysis may potentially be decreased by using small-volume intraplexus injections under real-time ultrasound guidance.5 However, since currently there is no clear evidence suggesting that phrenic nerve paralysis can be reliably avoided, this block is not recommended for patients with known low pulmonary reserve such as those with chronic obstructive pulmonary disease.
Furthermore, it is not recommended that the block be used in patients who are intoxicated, demented, or otherwise without normal mental status, as the patient’s report of paresthesias, worsening pain, or other symptoms during the procedure helps avoid complications from misdirected anesthetic (intravascular or intraneural injection). Also, postblock evaluation for peripheral nerve injury (PNI) will not be possible if a consistent neurologic exam cannot be performed before the procedure is started.
The brachial plexus originates from the anterior rami of the C5-T1 spinal nerves and divides into the roots, trunks, divisions, and cords that ultimately contribute to the axillary, radial, median, and ulnar nerves that provide cutaneous and motor innervation for the entire upper limb. After exiting the neural foramina, the brachial plexus travels through the interscalene groove between the anterior and middle scalene muscles and joins the subclavian artery anterior to the first rib and posterior to the clavicle. This neurovascular bundle travels to the axilla and supplies both motor and sensory innervation to the entire upper extremity via the axillary, musculocutaneous, radial, median, and ulnar nerves. When successfully performed, the interscalene block may also affect the distal branches of the divisions and cords that give rise to the suprascapular, lateral and medial pectoral, thoracodorsal, and subscapular nerves.