Axillary block: Median nerve rescue block

Axillary Nerve Block anatomy

• at the level of the axilla, the nerves are in their terminal branches
• the median, ulnar and radial nerves lie around the axillary artery and are blocked with a single injection. the musculocutaneous nerve however lies lateral to the axillary artery in the coracobrachialis muscle and requires a separate injection
• peripheral nerves in relation to the axillary artery
  • median nerve – anterolateral
  • ulnar nerve – anteromedial
  • radial nerve – posterior

Utility of the Axillary Nerve Block

• the axillary nerve block is good for surgeries involving the forearm, wrist, or hand
• in contrast to the infraclavicular nerve block, the axillary nerve block spares the musculocutaneous nerve which must be blocked separately
• if an upper arm tourniquet is to be used, an intercostobrachial nerve block must also be performed

Testing the Axillary Nerve Block

• median nerve
  • sensory: palm of hand (lateral portion)
  • motor: wrist flexion
• ulnar nerve
  • sensory: ulnar side of hand/fingers (4th and 5th digit)
  • motor: finger abduction against resistance
• radial nerve
  • sensory: dorsal surface of forearm and hand (lateral portion)
  • motor: wrist extension

Median Nerve Rescue Block

• If the axillary block fails to anesthetize the median nerve, wrist flexion and sensation over the lateral portion of the palm will be intact. In this instance, a supplementary block of the median nerve can be performed at either the elbow or the wrist.

• Median Nerve Block at the elbow
  • the median nerve passes medial to the brachial artery in the antecubital fossa
  • the nerve can be blocked utilizing paresthesias, nerve stimulation (finger/wrist flexion or pronation), or ultrasound guidance
  • the needle is inserted just medial to the palpated brachial pulse. When the nerve is located 5-7 ml of local anesthetic is injected
• Median Nerve Block at the wrist
  • at the wrist, the median nerve runs just lateral to the palmaris longus (PL) between the PL and the flexor carpi radialis (FCR). Of note, 20% of people do not have a PL.
  • at the wrist, nerve stimulation is not useful. Median nerve block at the level is a field block based on land marks or ultrasound guided
  • the needle is inserted between the PL and the FCR 2 cm proximal the to crease at the wrist. The needle is inserted approximately 2 cm and 3-5 ml of local anesthetic is injected as the needle is withdrawn.
  • care should be taken to avoid high injection pressures and limit the amount of local anesthetic to 5 ml; otherwise the nerve can become entrapped and compressed within the carpal tunnel resulting in nerve damage

Axillary Block: N block supplement

The axillary block is the most distal nerve blocked on brachial plexus. Used for surgeries of hand or forearm. Benefits: negligible risks of respiratory compromise 2/2 pneumothorax or phrenic nerve blockade, can tamponade artery if inadvertent puncture occurs. Review brachial plexus anatomy The goal is to block the nerves surrounding the axillary artery. Median, radial and ulnar nerves all travel with the axillary artery within the axillary sheath; the musculocutaneous nerve travels separately within the belly of the coracobrachialis muscle. **Must block musculocutaneous nerve separately!**