Axillary Plexus Block

Blockade of the brachial plexus in the axilla. This block:

Avoids the risk of pneumothorax associated with more proximal blocks
Gives better coverage of the ulnar artery
Traditionally was associated with poor blockade of the musculocutaneous nerve when performed with a landmark technique, but this is essentially moot when performed with ultrasound
Allows individual targeting of the four major nerves of the brachial plexus
- Radial nerve
- Median nerve
- Ulnar nerve
- Musculocutaneous nerve

Indications

Anaesthesia and analgesia for:
- Distal upper arm
- Forearm A-V fistula.
- Wrist and Hand
  e.g. carpal ORIF, carpectomy, metacarpal ORIF, proximal phalanx ORIF, fasciectomy, dupuytren’s contracture.
Sympathicolysis
Pain syndromes

The upper limb is supplied by the brachial plexus:

Formed by the anterior primary rami of C5 to T1
- Variably C4 to T2
Divided into roots, trunks, devisions, cords, and branches
Blocking the plexus at different levels will give a different distribution of sensory block.
Runs between the clavicle and third rib
Runs with the axillary artery into the upper limb, where it forms the major terminal branches

The brachial plexus has five key sections:

Five roots
The nerve roots that give rise to the plexus. May be imaged as they emerge from the vertebral foramen.
Three trunks
Roots merge together to form three trunks:
- May be imaged at the interscalene level
  Deep to SCM, between anterior and middle scalene. Key landmarks:
  - Lateral border of SCM
  - Scalenus anterior
  - Interscalene groove
- Superior trunk
  From C5 & C6.
- Middle trunk
  From C7.
- Inferior trunk
  From C8 and T1.
Six divisions
Three anterior and three posterior, which then re-merge to form the cords.
- Lie posterior and cephalad to the subclavian artery
- May be imaged at the supraclavicular level.
Three cords
Imaged wrapping around the axillary artery at the infraclavicular level, and include:
- Lateral cord
- Posterior cord
- Medial cord
Branches
- Divided into major and minor terminal branches
- Major terminal branches may be imaged in the axilla

The major terminal branches include:

Radial nerve
- Sensation to the dorsum of the hand, generally the lateral 2.5 digits.
- Motor: Extension of elbow and fingers
Median nerve
- Sensation to the palm, and the palmar surface and dorsum of the distal phalanges of the lateral 3.5 digits
- Motor: Flexion of fingers
Ulnar nerve
- Sensation to the medial 1.5 fingers, the ulnar border of the hand (including the dorsum), and sometimes the ulnar part of the forearm
- Motor: Flexion of 4^th and 5^th digits and opposition of 1^st digit
- Most effectively blocked with a targeted axillary block
Musculocutaneous nerve
- Sensation to the lateral aspect of the forearm
- Motor: Flexion and supination of forearm
Axillary nerve
- Sensation over the “regimental patch” of the shoulder

From the roots:

From the trunks:

From the cords:

Lateral pectoral nerve
Subscapular nerve
Thoracodorsal nerve
Median pectoral nerve
Intercostal brachial nerve
Medial brachial cutaneous nerve
Medial antebrachial cutaneous nerve Supplies upper medial part of the forearm, and can be covered with a subcutaneous bleb just distal to the axillary hairline.

Position
- Supine
- Head turned to contralateral side
- Position ipsilateral arm above head
  i.e. Externally rotated with 90° of abduction and elbow flexion.

Place US probe
- Perpendicular to skin
- In short axis along the line of pectoralis major
Identify axillary artery
Nerves are located mostly around the artery:
- Median is superoanteriorly
- Ulnar inferoposteriorly
- Radial posteriorly
- Musculocutaneous is located either:
  - Commonly in a facial plane between biceps brachii and coracobrachialis
  - Within coracobrachialis
Trace nerves to elbow and return
Place 5ml of LA around each nerve
Target deeper nerves first.