Interscalene Block

The brachial plexus is a nerve network that supplies the upper extremity. It is formed by C5-T1. It exits the cervical spine and travels between the anterior and middle scalene muscles and then travels distally around the axillary artery. The space between the scalene muscles is called the interscalene groove. This space is palpable behind the lateral head of the sternocleidomastoid muscle and adjacent to the C6 lateral tubercle, also known as Chaissaignac's tubercle. Under ultrasound visualization, the brachial plexus can be typically seen as 2 or 3 hollow circles ("stoplight") that correspond with the superior, middle, and inferior trunks. The inferior trunk can sometimes be difficult to visualize as the muscle gets thicker. Once visualized, injection of a long-acting local anesthetic can block nerve impulses and cause upper extremity numbness and weakness. Structures immediately distal to the nerve block placement consistently block nerve impulses and causes sensory and movement loss. A regional anesthesia specialist usually performs an interscalene block. It is commonly performed in the preoperative suite or postanesthesia care unit with the patient mildly sedated. The interscalene block covers most of the brachial plexus, sparing the ulnar (C8-T1) nerve. It is a great block for distal clavicle, shoulder, and proximal humerus procedures. Under sterile conditions, the interscalene space is identified either by palpation or ultrasound visualization. A nerve stimulator can also be used as an adjunct to confirm placement. The nerve stimulator causes muscle contractions in the deltoid muscle, arm, or forearm when the corresponding nerve is stimulated. A volume of local anesthetic is injected, typically between 15-25mL. Commonly used local anesthetics include bupivacaine and ropivacaine. Once the local anesthetic is placed, the patient can expect pain relief and limb heaviness for the duration of local anesthetic action. Side Effects Side effects and complications of an interscalene block can be divided into 2 parts. Needle and Local Anesthetic Placement A misguided needle placement can result in pneumothorax, nerve damage, epidural or intrathecal placement, and spinal cord trauma. Ultrasound use can decrease this risk. Patients with pulmonary comorbidities can also complain of shortness of breath post-block placement due to the blockage of the phrenic nerve. The phrenic nerve traverses anterior to the brachial plexus and can be affected when the volume of local anesthetic travels more proximally. The volume of local anesthetic can also spread posteriorly and affect the cervical plexus, which results in Horner syndrome (ptosis, miosis, and anhidrosis). Local Anesthetics Monitoring for local anesthetic toxicity during block placement is required. Commonly used local anesthetics have a maximum dose allowed, and knowledge of these values by the provider is important. Allergic reactions to amide local anesthetic are uncommon; however, ester local anesthetics have para-aminobenzoic acid (PABA), a known allergen.