Axillary Block

Indications

• Surgery or manipulation of the elbow, forearm or hand.

Set-Up

• Two 30 ml syringes with local anesthetic (1.5% mepivacaine + epinephrine (1:200,000) + HCO3 - (0.1 meq/cc)
• For longer acting blocks, 10 ml of 0.75% bupivacaine + epinephrine (1:200,000) may be added.
• The syringes are attached to a three-way stopcock that is connected to IV extension tubing fitted to a 23 gauge, 1” needle. This provides an immobile needle technique.

Essential Anatomy

• Terminal branches of the brachial plexus are arranged circumferentially around the axillary artery. (Fig 1-1)
• The only essential topical landmark is the most proximal point where the axillary pulse can be palpated.

Technique

• Place the patient supine with arm extended out at 90° from the body on a hand table with the palm facing up. Alternatively, the arm can be flexed at the elbow and the shoulder abducted with the patient’s hand positioned palm side up behind the head.
• Sedation may be given in order to diminish anxiety and discomfort, as well as protect against the systemic reaction of an unexpected intravascular injection (benzodiazepines raise the seizure threshold). Care should be taken not to oversedate the patient for fear of masking a paresthesia or pain caused by intraneural injection.
• Clean the axilla in an aseptic manner. Palpate the axillary artery as proximally as possible. Compress the artery with the tips of your fingers or use one finger along the axis of the artery to fix the artery against the head of the humerus. Insert the needle over the pulse while having an assistant gently aspirate as the needle is advanced. Once arterial blood is detected, advance slowly until blood flow ceases. Inject 3-5 ml of local anesthetic as a test dose. If no signs of intervascular or interneural develop, the remaining local anesthetic is administered with aspiration. every 3-5 ml. The relationship of the needle to the sheath may change as local anesthetic is injected, so at least one reassessment is recommended by withdrawing the needle back into the axillary artery and re-advancing the needle out of the artery and into the sheath. The downside to repeatedly confirming location is that blood, an irritant to the nerves, may be inadvertently introduced within the sheath and could cause postoperative discomfort. It is not unusual to detect blood-tinged local anesthetic during subsequent aspirations; this has been described as “sheathy fluid” and suggests proper needle positioning within the axillary sheath.
• After delivering the appropriate dose, the needle is removed and pressure is applied to the site of injection for a minimum of five minutes. This reduces hematoma risk and theoretically promotes cephalad spread of local anesthetic to block the musculocutaneous nerve.
• Success rate of blockade of all 4 nerves approach 95% with 60 mls of local anesthetic.

Limitations

• Late or incomplete blockade of the musculocutaneous nerve (Fig 1-2).

 

• Requires abduction of the arm which my be difficult in arthritic patients or those with a frozen shoulder.
• Transarterial technique contraindicated in anticoagulated or coagulopathic patients.

Figure 1-2

Complications

• Hematoma
• Neuropraxia
• Local anesthetic toxicity

Pearls

• Insure that the blood aspirated is arterial blood and not venous. The axillary vein is located outside the sheath in approximately 5 to 10 percent of patients. When in doubt, disconnect the siringe and leave the tubing open to air so to better appreciate the pulsitile arterial flow.
• Due to its proximal exit from the sheath, the musculocutaneous nerve is often missed or slow to be blocked. This can be overcome by using a sufficiently large volume of local anesthetic with distal compression of the sheath following injection. If biceps relaxation or an insensate lateral forearm is essential, the musculocutanous nerve can be selectively blocked by injecting 5 to 10 ml of local anesthetic into the coracobrachialis muscle.
• When surgery involves the skin medial and proximal to the elbow, 5-10 cc of subcutaneous local can be injected in the axilla to block the intercostobrachial nerve.
• Controversy exists as to the approach if a paresthesia is elicited during an attempted transarterial block. Some use the parasthesia as an indication of proximity to the brachial plexus and inject local anesthetic when one is elicited while others will withdraw and re-direct away from the area.

References

1. De Jong Rh: Axillary block of the brachial plexus. Anesthesiology 1961; 22:215.
2. Lanz E, Theiss D, Jankovic D: The extent of blockade following various techniques of brachial plexus block. Anesth Analg 1983;62:55.
3. Winnie AP: Plexus anesthesia, perivascular techniques of brachial plexus block. In (eds): 2nd edition, p 185. Philadelphia, W.B. Saunders Co, 1990.
4. Winnie AP, Radonjic R, Akkinemi SR, Durrani Z: Factors influencing the distribution of local anesthetics in the brachial plexus sheath. Anesth Analg 1979;58:225.

These technique descriptions are presented for educational purposes and are not intended to substitute for actual hands-on training.