Peripheral Nerve Blockade: Axillary BlockBien S. TardoPost-Graduate Intern

Provide longer & more localized pain relief than neuraxial techniques

Avoid side effects of systemic medication

Premedication & Sedation Although a mild dose of opioid (50 to 100 μg of

fentanyl) will help ease the discomfort of nerve localization, patient responsiveness must be maintained

Small doses of propofol or midazolam may provide excellent amnesia at levels of consciousness that still allow cooperation

Upper Extremity

Innervation is derived from 5 closely approximated nerve roots, extending from C5 to T1 (brachial plexus)

Produce the terminal nerves of the arm & hand

Major Motor Function of the Individual Nerves of the Brachial Plexus

Nerve Major Motor Function

Axillary Abduction of the shoulder

Musculocutaneous Flexion of the elbow

Radial Extension of the elbow, wrist, & finger

Median Flexion of the wrist & finger

Ulnae Flexion of the wrist & finger

Brachial Plexus: Axillary Technique• Carries the least chance of

pneumothorax• Nerves are anesthetized around the

axillary artery, where they have regrouped into their terminal branches

• Because of the observation that the single sheath may be broken up into separate compartments by fascial septa surrounding individual nerves in the axilla, local anesthetic should be injected at multiple sites in the axilla

Tourniquet Placement Placement of a blood draw type tourniquet distal to the

injection site encourages proximal movement of the anesthetic within the axillary sheath

The tourniquet is placed while the arm is at the patient’s side

If the tourniquet is placed as high as possible on the patient’s arm before abduction of the arm, the tourniquet will generally be very close to the ideal location of 3 cms from the axillary crease upon abduction

The tourniquet is left in place for 10 mins following the injection

Approach The nerves that will be blocked lie w/in

a neurovascular sheath As the Medial, Posterior, & Lateral

cords of the Brachial Plexus enter the arm they divide into the Median, Radial, Ulnar, Musculocutaneous & Axillary Nerves

The Axillary Artery (becoming Brachial Artery) & Axillary Vein are within the neurovascular sheath at this level as well

Median & musculocutaneous nerves lie on the superior aspect of the artery

Ulnar & radial nerves lie below & behind the vessel

1. The patient lies supine with the arm extended 90 degrees from the side & flexed at the elbow

Extension beyond 90 degrees potentially compresses the axillary artery because of the pressure from the head of the humerus & may make identification of the landmarks more difficult

2. Axillary artery is marked as high in its course in the axilla as is practical

Usually felt in the intramuscular groove between the coracobrachialis & triceps muscles

Also passes between the insertions of the pectoralis major & latissimus dorsi muscles on the humerus

3. After aseptic preparation, a skin wheal is raised over the proximal portion of the artery

Index & middle fingers of the nondominant hand straddle the artery just below this point, both localizing the pulsation & compressing the neurovascular bundle below the intended site of injection

Transarterial Takes advantage of the fact that the axillary artery is w/in

the neurovascular sheath By going through the artery, anesthetic is placed reliably

within the neurovascular sheath, & can then diffuse, over time, into the nerves

Palpation of the artery should be done with several fingers to better localize the vessel

Transarterial By palpating immediately proximal to the tourniquet, &

injecting proximal to the palpating fingers, the physician is able to inject very proximally on the arm

This will ensure the highest probability of success Though relatively superficial, the axillary artery can be

difficult to palpate in some patients, & time should be spent to ensure accurate localization

2 fingers of equal length straddle the artery while the needle is introduced along its long axis with a central angulation

The palpating fingers serve not only to identify the vessel but also to compress the perivascular sheath & encourage spread of anesthetic solution centrally

Injection

A 5/8 inch straight 25 gauge or ¾ inch 25 gauge butterfly needle (with extension tubing) is preferred

The needle is inserted toward the palpated artery When a flash is seen, insertion is continued until blood

return ceases A <0.5ml volume is then injected to clear the

hub/extension tubing & aspiration is repeated to confirm position immediately behind the artery

Injection

The injection is then performed in 5.0 ml increments, aspirating between injections to ensure that the correct position has been maintained

When 5.0 ml remains, the needle is slowly withdrawn through the artery, until blood return ceases

A <0.5ml volume is then injected to clear the hub/tubing, & aspiration repeated to confirm position immediately superficial to the artery

The last 5.0 ml is then injected, & the needle withdrawn

Injection

Aspirate every 5 ml to ensure that the needle has not inadvertently entered an artery or vein

Monitor for signs & symptoms of intra-arterial injection including: increased heart rate, “funny” metallic taste faintness seizures

Some clinicians will inject half of the total local anesthetic dose posterior to the artery & the other half anterior to the artery

Perivascular Rather than penetrating the artery, the artery is

carefully localized, & the anesthetic injected at the same depth as the artery, both superior, & inferior

5 to 10 mL of local anesthetic is injected closely on each side of the artery, using multiple passes with a moving needle not seeking nerve responses, producing a “wall of solution” that intercepts the paths of each of the branches

When properly localized, the neurovascular sheath will display the same sausage-like swelling post injection as is seen with the transarterial method

Perivascular

After initial infiltration, sensation or motor function is tested in the peripheral nerve distribution w/in 5 mins

If anesthesia is not present, reinjection of the area is again performed with multiple passes

Simpler & can be performed rapidly, but requires clear identification of the pulse

Anesthetic mixturesDuration Drug Dosing Volume Comments

Short

<40 minutes

Lidocaine 0.5% 5.0 mg/kg

1 ml per kg body weight

Dilute 1.0 % lido 1:1 with

normal saline to

maximum of 50 ml

Use 40 ml for small adults

<50kg

Medium

40-90 minute

Lidocaine 0.5% with

epinephrine

5 mg/kg

1 ml per kg body weight

Dilute 1% lido 1:1 with

normal saline to

maximum of 50 ml

Use 40 ml for small adults

<50kg

Long

>90 minutes

Lidocaine 1.0% with

epinephrine

Bupivicaine 0.25%

20 ml lidocaine with

epi.

 

20 ml 0.25%

Bupivicaine

 

Dilute with normal saline

to total of 50 ml

Use 15 ml Lidocaine/15 ml

Bupivicaine/10.0 ml saline for

small adults <50kg

Complications

Neuropathy is the foremost consideration Hematoma can occur if the vessel is punctured, but

this is rarely a problem

Pitfalls of ANB

1. Infiltrating too deep As already noted, the neurovascular compartment is very

superficial If the needle is advanced too far beyond the artery you will

inject deep to the neurovascular compartment, & a block will not be achieved

The correctly performed injection into the neurovascular compartment produces a “sausage like”, confined, subcutaneous swelling, that is easily seen in all but the most obese patients

Pitfalls of ANB

2. Using too small a volume of anestheticThe ANB is a volume dependent technique At least 40 ml is needed to diffuse adequately in the adult

patient When using the transarterial/perivascular techniques the

objective is to fill the neurovascular compartment with anesthetic that then diffuses into the nerves

An adequate volume is required to both surround the nerves, & to move proximally far enough to reach the musculocutaneous/ proximal nerves

Pitfalls of ANB

3. Attempting procedure too soon Immediate rest pain control is generally achieved with a

properly placed injection If a gentle manipulation is attempted immediately after the

block, however, some pain will still be felt The person performing the reduction in this case should be

instructed to wait before performing the procedure A significant number of patients will be ready at 5 mins, but

the density of anesthesia will generally increase for 20-30 mins

Pitfalls of ANB

4. Not injecting proximally enough on the arm The more proximally on the arm the ANB is performed the

more likely it will be complete The musculocutaneous nerve has already left the

neurovascular bundle at the point where the injection is performed: consequently, proximal placement of the anesthetic is required