Intrascalene block: anatomy

Anatomy

The interscalene nerve block is performed at the C6 level (level of the cricoid cartilage) between the anterior and middle scalene muscles.

1. Place the patient supine with head turned to the opposite side to be blocked.
2. Identify the sternocleidomastoid. By having the patient slightly raise his head, the scalene muscles behind the SCM tense and you can identify and mark the groove between the anterior and middle scalenes (posterior and lateral to the SCM).
3. Mark the level of the cricoid thyroid, C6.
4. Place needle perpendicular to all planes at the C6 level within the groove and advance until you get nerve localization you want, usually a motor response in the deltoid or biceps. If you hit tubercle, withdraw needle and redirect in an anteroposterior plane.

Indications

1. Distal shoulder
2. Arm
3. Elbow surgery

Ulnar distribution is the most commonly missed!

Complications

Related to inadvertently hitting structures located in the vicinity

1. Pneumothorax – if needle directed too caudad; should be considered if patient has chest pain, SOB or cough.
2. Spinal or epidural anesthesia – if needle directed too medially and enters the intervertebral foramina.
3. Intravascular injection – the vertebral artery lives in the canal of the transverse process
4. Hematoma formation

Side Effects

Related to the spread of local anesthetic to nearby structures

1. Diaphragm paralysis – due to phrenic nerve blockade
2. Horner’s Syndrome – due to spread to the sympathetic chain. Ptosis, anhidrosis and miosis. May also see nasal congestion due to the sympathectomy.
3. Hoarse voice – due to spread to the recurrent laryngeal nerve