Axillary Block

An axillary block targets the brachial plexus at the level of the terminal nerve branches appropriate for surgeries of the distal upper extremity. Multiple techniques are described for this block including transarterial, paresthesia seeking, and nerve stimulator approaches.

Indication

As primary anesthesia and/or postoperative pain management with or without a continuous catheter for forearm, hand, and wrist surgeries.

Technique Preparation

Arrange sterile towels, sterile gloves, gauze pads, marking pen, antiseptic solution, peripheral nerve stimulator, syringes, and needles for local infiltration and nerve block placement.

Dose

30-40 ml syringes of local anesthetic. Needles

25 g 1.5 in. needle for skin infiltration and a 22 g, 3 or 5 cm short bevel insulated stimulation needle.

Agents

3% chloroprocaine, 2% lidocaine, 0.5% ropivacaine, 0.5% bupivacaine.

Surface Anatomy and Landmarks Landmarks

Landmarks include axilla, axillary artery, and humerus (Fig. 20.6). Imagining the upper arm (just distal the axillary hair pad) in cross-sectional view, the musculocutaneous nerve is typically found outside the neural vascular bundle and in the 9-12 o'clock position embedded in the coracobrachialis muscle; the median nerve is usually located (within the neural vascular bundle) in the 12-3 o'clock quadrant (above the pulse of the axillary artery). The ulnar nerve is often located in the 3-6 o'clock position and radial nerve (below the pulse of the axillary artery) varied in the 6-9 o'clock position, both branches within the neural vascular bundle.

The patient is positioned supine with their head neutral or turned away from the side to be blocked. The arm to be blocked is abducted 90° at the shoulder and flexed 90° at the elbow. Axillary artery is palpated and its course marked followed by skin preparation and local skin

Figure 20.6 Landmarks for the approach to the axillary brachial plexus block. B biceps muscle, T triceps muscle, CB coracobrachialis muscle. Line #1 indicates pulse of the axillary (brachial) artery.

infiltration. A 22-gauge 3-5 cm b-bevel needle is connected to a nerve stimulator set at 1.0 mA (activate nerve stimulator subsequent to subcutaneous needle placement) and while palpating the axillary artery, the needle is inserted in the distal axilla aimed 30-45° to the skin directed toward the axilla directly overlying the palpable artery. The needle is inserted searching for appropriate motor response at a stimulation of between 0.2 and 0.5 mA or eliciting a paresthesia to the wrist, hand, or thumb. A consistent muscle twitch of the wrist and hand reflecting ulnar, radial, and/or median nerve stimulation is appropriate for injection. A total of approximately 30-40 ml of local anesthetic is injected following a negative aspiration for blood and again aspirating frequently during delivery of the anesthetic in small aliquots. Keeping in mind the clockwise arrangement ofthe three nerves within the neural vascular bundle (ulnar, radial, and median), each quadrant should have local anesthetic injected in order to insure the blockade of each terminal nerve branch. Local anesthetic should be injected in at least two locations around the artery (superficial and deep) and within the neural vascular bundle to increase success of the block. A continuous single orifice catheter may be inserted to provide continuous infusion of local anesthetic. The musculocutaneous nerve branches early (higher in the axilla) from the brachial plexus and passes into the coracobrachialis muscle, therefore the musculocutaneous nerve must usually be blocked outside the neurovascular bundle within the belly of the coracobrachialis muscle. Musculocutaneous nerve blockade is achieved by inserting the block needle into and through the coracobrachialis muscle until contacting the humerous and then pulling back a few millimeter off the periosteum prior to injection.

Pitfalls and Pearls Pitfalls

Intravascular injection (with possible local anesthetic toxicity), hematoma formation, nerve injury, and infection are potential complications of an axillary block. Positioning of the extremity for this block (abducting the arm, especially if there is a shoulder injury) may prove difficult.

Pearls

An axillary block lacks the same risk of pneumothorax compared to other approaches of the brachial plexus. If a tourniquet of the upper extremity is to be used, the additional blockade of the medial brachial cutaneous and intercostobrachial nerves within the axilla must be performed to provide anesthesia of the skin overlying the medial upper arm.

Clinical Uses Surgical

• Elbow surgery, including epicondylitis

• Forearm surgery, including distal AV fistula surgery

• Wrist surgery, including posterior synovial cyst removal, carpal tunnel release, and Colles' fracture repair

• Hand surgery, including Dupuytren's contracture release

Postoperative analgesia

For all the surgeries indicated above.

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