Intrascalene block: anatomy


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


Ulnar distribution is the most commonly missed!


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