The brachial plexus at the interscalene level is located just lateral to the carotid artery within the interscalene groove consisting of the anterior and middle scalene muscles. This block is performed at the level of the cricoid cartilage but is more importantly performed at the level where the brachial plexus is optimally visualized by ultrasound. This may be patient dependent. The brachial plexus at the level of the cricoid cartilage is described as being oriented in a vertical arrangement where the C5, C6 and C7 nerve roots are visualized by ultrasound.
The patient is positioned in the supine position slightly head up. The ultrasound probe is placed cephalad to the the clavicle and the subclavian artery is identified. The brachial plexus will be identified just lateral to the subclavian artery. The ultrasound probe is then moved superiorly following the brachial plexus to the level of the cricoid cartilage. The C5, C6 and C7 nerve roots will be easily identified by ultrasound (image 1). The block needle is inserted posteriorly using the in plane approach (image 2). The block needle should be visualized by ultrasound at all times. A nerve stimulator may be used to help identify the brachial plexus. As the needle approaches the brachial plexus a motor response from the biceps muscle or muscle groups below the elbow should be elicited. Local anesthetic, 10-20 ml, is injected and distribution should be visualized around the brachial plexus. The needle may be moved while visualized by ultrasound. to ensure even spread of the local anesthetic. It should be noted that the local anesthetic should be easy to inject without paresthesia. Epinephrine may be added to the local anesthetic to ensure an intravascular injection has not occurred.
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