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Axillary Block (AXB) is a simple and effective axillary block that is widely used in anesthesia and perioperative analgesic management of forearm surgery. With the application of ultrasound visualization in clinical anesthesia, the accuracy of AXB has also improved, but many anesthesiologists still have many questions about the complex neuroanatomy of the brachial plexus, the innervation area, and how to better improve the anesthesia effect. Therefore, in this tweet, AXB will be described in detail and the confusion encountered in clinical work will be answered.
Brachial plexus anatomy
The brachial plexus block has undergone nearly 140 years of development and evolution and is not only one of the oldest regional nerve blocks, but also plays an important role in perioperative anesthesia and pain management [1]. First of all, let's understand the brachial plexus, the brachial plexus is composed of most of the anterior branch of the C5-8 cervical nerve and the anterior branch of the T1 nerve, through the anterior and middle scalene muscle gaps, walking behind and above the subclavian artery, and entering the axillary after the posterior clavicle is divided into three main nerve trunks: the upper trunk (C5-6), the middle trunk (C7), and the inferior trunk (C8, T1) The three trunks are divided into two anterior and posterior strands at the middle and outer edges of the first rib after the clavicle, and the six femoral nerves form three bundles at the axillary (upper trunk, The anterior femur of the middle trunk forms the lateral tract, the anterior femur of the inferior trunk becomes the medial tract, and the posterior femur of the three trunks forms the posterior fascicle), each fascicle divides the nerve branch in the coracoid plane, the lateral fascicle divides the musculocutaneous nerve, the posterior fascicle divides the axillary and radial nerves, and the medial fascicle divides the ulnar nerve and median nerve medial head [2].
For ease of understanding, it is shorthand as follows: 5 roots, 3 stems, 6 strands, 3 bundles, and 5 branches. 5: C5, C6, C7, C8 and T1
3 stems: upper trunk (C5, 6), middle trunk (C7), lower trunk (C8, T1) 6 strands: each stem is divided into front and rear strands
3 bundles: posterior fascics (posterior femoral-axillary artery of the three trunks), lateral fascicles (lateral to the anterior femoral-axillary artery of the superior and middle trunks), medial fascicle (medial aspect of the anterior femoral-axillary artery of the inferior trunk) 5 branches: musculocutaneous nerve, ulnar nerve, radial nerve, median nerve, axillary nerve
Armpit brachial plexus
The bundles of the brachial plexus pass under the axillary from behind the inferior border of the pectoralis minor muscle to form terminal branches, which are the radial, ulnar, median, and musculocutaneous nerves, respectively. AXB is one of the most commonly used peripheral nerve blocks in forearm and hand surgery for many years [3,4], with no risk of phrenic nerve palsy, spinal cord, or vertebral artery injury compared with interscalene brachial plexus block, and no risk of pneumothorax compared with the supraclavicular brachial plexus block approach. Therefore, compared with the latter two, the AXB operation is relatively simple, with a low risk of complications [5], and has the characteristics of rapid onset, good analgesic effect, and low impact on circulation, which is conducive to postoperative rehabilitation [6].
Let's take a closer look at each terminal branch:
The median nerve is the thickest and most superficial of all the terminal nerves, originating from the medial and lateral fascicles, and accompanies the axillary artery in the upper arm. It gives out the volar sensory branches of the thumb, index finger, middle finger, and lateral half of the ring finger. The following diagram shows the median nerve composition, travel, innervation of muscular branches and sensory areas:
When the median nerve is stimulated with a nerve stimulator, the wrist may be flexed, the second and third fingers flexed, the thumb extended, and the forearm internally rotated. As shown in the figure:
The ulnar nerve is a continuation of the medial tract and runs medial to the axillary artery along with the medial forearm cutaneous nerve. The ulnar nerve gives out articular branches that innervate the elbow joint and muscular branches that innervate the hand and forearm. In addition, the ulnar nerve gives out the sensory branches of the ring and little fingers.
When the ulnar nerve is stimulated with a nerve stimulator, the wrist may be flexed, the fourth and fifth fingers may be flexed, and the thumb may be adducted. As shown in the figure:
The radial nerve is a continuation of the posterior fascicle, running behind the axillary artery, exiting the axilla below the teres major, between the humerus and triceps, and giving out branches innervating the triceps, brachioradialis, and extensor radialis muscles, and the cutaneous branches innervating the lateral aspect of the arm and the dorsal aspect of the forearm and hand.
When the radial nerve is stimulated with a nerve stimulator, all fingers extended, wrists extended, elbows straightened, and forearms abducted. As shown in the figure:
The musculocutaneous nerve is an important branch of the lateral bundle that passes through the coracobrachialis muscle and descends between the biceps and brachii muscles and innervates the biceps and brachii muscles. It continues to migrate distally, giving out the lateral forearm cutaneous nerve and from the deep fascia of the biceps and brachioradialis muscles to the superficial part of the cubital fossa. In the cubital fossa, this nerve emits a cutaneous sensory branch on the lateral aspect of the forearm.
Elbow flexion may occur when the musculocutaneous nerve is stimulated with a nerve stimulator. As shown in the figure:
Ultrasound-guided axillary brachial plexus block
The patient is supine, the arm is abducted at 90 degrees, the upper arm is externally rotated, the probe is placed at the axillary striae, and the needle is inserted in the plane.
The anatomical marker is first looked for the axillary artery, which is medial to the axillary artery and can be compressed by the pressure of the probe. Next, look for the next key anatomical landmark, the symphysis tendon, which is the joint tendon of the latissimus dorsi and teres major, located below the axillary artery, where the radial, ulnar, and median nerves accompany the axillary artery, and the radial, median, and ulnar nerves are located in the deep, posterior, and anterior aspects of the axillary artery, respectively. The specific location is shown below:
It should be noted that the location of the target nerve around the axillary artery varies greatly from individual to individual, especially when the ultrasound probe is placed, which can easily lead to changes in the position of the nerve by applying pressure to the tissue. Jin et al. [7] performed ultrasound-guided AXB on 131 patients and found that the most common locations were 10-11 o'clock in the median nerve (79.2%), ulnar nerve at 1-2 o'clock (79.3%), radial nerve at 3-5 o'clock (78.4%), and musculocutaneous nerve at 8-9 o'clock (86.9%). As shown in the figure: (M-median nerve, U-ulnar nerve, R-radial nerve, MC-musculocutaneous nerve).
Jones et al. [8] performed AXB on ultrasound in 162 patients, with musculocutaneous nerves located between 2 o'clock and 5 o'clock on a semicircular template of the clock, with the majority (95.4%) located at 3 and 4 o'clock, and the most common MCN shapes were plano-oval and oval (87.1% in total). At the same time, it has been noted that the posture or position of the shoulder also affects the position of the musculocutaneous nerve [9].
Other branches
In addition to the conventional four branches innervating the hand described above, there are axillary nerves from the posterior fascicle, brachial intercostocarpal nerves from the second intercostal nerve, and medial brachial cutaneous nerves from the medial fascicle. Blocking the above branch nerves is very important for a well-established brachial plexus, especially to prevent tourniquet discomfort. Except for the axillary nerve and musculocutaneous nerve, which branch off from the lateral and posterior tracts of the brachial plexus at a higher position, the other nerves are distributed around the axillary artery.
The intercostal brachial nerve (T2) is not a component of the brachial plexus, but originates from the posterior branch of the lateral cutaneous branch of the T2 intercostal nerve and consists of the lateral cutaneous branch of the 1st and 3rd intercostal nerves.
The medial brachial cutaneous nerve (C8-T1) originates from the medial bundle of the brachial plexus, is located medial to the axillary vein, and is distributed in the skin of the medial arm and anterior arm. The medial forearm cutaneous nerve (C8-T1) arises from the medial bundle of the brachial plexus, is located between the axillary arteries and veins, and is superficially associated with the essential vein, and is distributed in the medial forearm area, anterior and posterior skin.
summary
Axillary brachial plexus block has a definite analgesic effect and less impact on breathing and circulation, bringing a more comfortable experience and a safer guarantee for patients, and becoming an anesthesia skill that anesthesiologists must master.
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bibliography
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