Continuous Axillary Block

The advantages of continuous brachial plexus block include prolonged postoperative analgesia and sympathectomy.^1,2
The types of surgical procedures appropriate for continuous axillary block include extensive hand, wrist, or forearm surgery where considerable postoperative pain is anticipated. Continuous axillary block is particularly indicated in digital replantation or hand and forearm free-flap microvascular surgery. By providing a prolonged sympathectomy, the block may improve arterial inflow by vasodilating the feeder arteries to replanted tissue. This is evidenced by increased temperature of the upper limb following brachial plexus blockade.³ However, the risk of producing a steal phenomenon, in which dilation of surrounding normal vessels redistributes flow away from the replant, is real.⁴

The axillary "sheath" is identified using a "loss of resistance" technique.
In patients with easily-defined anatomic landmarks, the neurovascular bundle surrounding the axillary artery lies close to the surface and is easily palpated in a groove between the coracobrachialis muscle and the triceps brachii. Entry into the neurovascular bundle with a needle can be confirmed through the use of a loss of resistance to saline technique. Alternative methods include eliciting paresthesias, using a nerve stimulator, or simply feeling the sensation of a "pop" as the needle pierces the fascia surrounding the neurovascular bundle.

The Technique
As in the performance of a simple axillary block, the patient is positioned with the arm abducted 90 degrees and the elbow flexed (Figure). Light sedation avoids blunting the detection of paresthesias.

Careful attention is paid to a sterile prep and drape of the axilla.

The neurovascular bundle lies in a groove between the biceps and coracobrachialis superiorly and the triceps inferiorly (Figure).

The axillary artery and surrounding neurovascular bundle is identified by palpation (Figure).

A wheal of dilute local anesthetic is raised on the skin directly overlying the axillary artery (Figure). A small nick through the skin is made with the sharp standard bevel of an 18 gauge needle to facilitate passage of the blunt 18 gauge needle and cannula.

A loss of resistance syringe charged with saline is attached to an 18 gauge 1 1/2 inch short-beveled needle and plastic cannula (Figure). The short-bevel needle is recommended to avoid trauma to the artery and nerves. Alternatively, an 18 gauge cannula and standard-bevel needle used for intravenous cannulation can be used. In either case, the needle is held with the bevel facing down and parallel to the skin. This presents a blunt surface to the skin and fascia, accentuating the loss of resistance.

The nondominant hand palpates the axillary artery while the dominant had directs the needle at a 45 degree angle to the skin directed along the path of the artery (Figure). Tension on the artery directed distally and against the humerus prevents motion of the elements of the neurovascular bundle as the blunt needle "pops" through the fascia.

The plastic cannula is advanced into the sheath (Figure). Injection of a small volume of saline through the cannula may open up the space and facilitate the passage of the indwelling catheter.

A 20 gauge (epidural-type) catheter is advanced through the cannula (Figure). Paresthesias elicited by passage of the catheter indicate successful placement within the sheath. Failure of the catheter to advance easily beyond the tip of the cannula strongly suggests that the cannula lies outside of the sheath and the procedure should be repeated.

The cannula is removed while the catheter is held in place (Figure).

Aspiration through the catheter is performed to detect intravascular placement of the catheter (Figure). An epinephrine-containing test dose of local anesthetic containing is also injected. The initial volume of local anesthetic is injected in incremental doses (40-50 cc of 1.5 % lidocaine or mepivacaine, or 0.375% bupivacaine). An infusion of local anesthetic is started (0.25% bupivacaine at 6-10 cc/hr).⁵

The catheter is secured by suture fixation to the skin and dressed with a bioocclusive dressing and tape.

In addition to the usual complications of axillary block, infection can occur as a complication of the indwelling catheter.
Injury to the axillary artery with subsequent hematoma formation and vascular insufficiency, neural injury, systemic local anesthetic toxicity from intravascular placement of the catheter, and infection are all complications of the continuous catheter technique.⁶

REFERENCES HOME