Blocks of the brachial plexus and the terminal nerves using a single-injection technique require a large volume of local anesthetics and their diffusion through several barriers before reaching the nerves. In addition, it has been established that with a single-injection technique the intensity of the block is not uniform among the nerves. Thus, the block of the brachial plexus using a single-injection technique with an interscalene approach often misses the ulnar nerve, and with an axillary approach it often misses the musculocutaneous or the radial nerve.
In a recently published meta-analysis of single-, double-, and multiple-injection techniques for axillary brachial plexus block, Handoll and Koscelniak-Nielsen (2006) reported a statistically significant decrease in primary anesthesia failure (RR 0.24, 95% CI 0.13 to 0.46) and incomplete motor block (RR 0.61, 95% CI 0.39 to 0.96) in the multiple-injection group as compared to those in the single-injection group. Similarly, when comparing multiple with double injections the meta-analysis showed a statistically significant decrease in primary anaesthesia failure (RR 0.23, 95% CI 0.14 to 0.38) and incomplete motor block (RR 0.55, 95% CI 0.36 to 0.85) in the multiple-injection group versus the double-injection group.
The time for block performance was significantly shorter for single and double injections compared with multiple injections, but the requirement for supplementary blocks in these groups tended to increase the time to readiness for surgery. This provides evidence that multiple-injection techniques using nerve stimulation for axillary plexus block provide more effective anesthesia than do either double- or single-injection techniques.
Moreover, with the introduction of imaging techniques for peripheral nerve block placement, the importance of needle reorientation to optimize the diffusion of the local anesthetic solution around different nerves and branches involved in the nerve block has become even clearer.
In this chapter we discuss general principles of multistimulation for the most commonly used approaches to the brachial plexus block. Multistimulation has been reported with axillary, interscalene, midhumeral and infraclavicular approaches to the brachial plexus. However, considering the greater number of needle passes in the proximity of the pleural cavity and large blood vessels that cannot be compressed in case of unwanted vascular puncture, multistimulation with the infraclavicular approach should be reserved for those with significant experience.
Interscalene Multistimulation Technique
To perform an interscalene block using a multistimulation technique, three different muscular responses should be elicited: (a) contraction of the deltoid muscle, induced by stimulation of the superior trunk (C4-5 roots); (b) contraction of the biceps with flexion of the forearm, induced by stimulation of the middle trunk (C6 root); and (c) contraction of the triceps muscle with extension of the forearm, induced by stimulation of the inferior trunk (C7 root).
Patient Position: Supine, with the head slightly turned away from the side where surgery will be performed.
Needle Size: A 22-gauge, 25-mm insulated needle.
Volume: 6 to 8 mL per trunk.
Anatomic Landmarks: The interscalene groove formed by the anterior and middle scalene muscles is palpated at the level of the cricoid cartilage (C6). This can be facilitated by palpating the posterior border of the sternocleidomastoid muscle and rolling the finger laterally and posteriorly to feel the scalene muscle. If the groove is not palpated, the patient can be asked to take a slow and deep breath to facilitate its location. The interscalene groove is marked. Next a horizontal line is drawn at the level of the cricoid cartilage. The site of introduction of the needle is the intersection between these two lines.
Approach and Technique: The insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced at a 45° angle, in a caudal and posterior direction, and is advanced slowly until it produces a specific motor response. The first motor response usually observed is the contraction of the deltoid muscle (superior trunk). The position of the needle is then adjusted to maintain the same motor response with a current of 0.5 mA. For shoulder surgery this is the most predictive response of a good block, deserving a larger part of the local anesthetic volume. Thus, after negative blood aspiration, 8 mL of local anesthetic solution is injected slowly. Next, the insulated needle is withdrawn to the level of the skin and the intensity of the current is increased to 1.5 mA. The needle is then reintroduced in a slightly more caudal direction (3° to 5°) toward the midpoint of the clavicle and the groove between the pectoralis major and deltoid muscles, in search of stimulation of the middle trunk (contraction of the biceps muscle with flexion of the forearm). After positioning the needle to allow for an appropriate motor response with a current of 0.5 mA, 6 mL of local anesthetic is injected following negative aspiration for blood. The insulated needle is again withdrawn to the level of the skin, and the intensity of the current set back to 1.5 mA. The needle is reintroduced in a slightly more caudal direction (3° to 5°) in search of a stimulation of the inferior trunk (contraction of the triceps muscle with the extension of the forearm). After the appropriate motor response is maintained with a current of 0.5 mA, another 6 mL of local anesthetic is injected slowly following a careful aspiration test.
1. The first motor response determines how the needle needs to be redirected next.
2. To extend the block posteriorly, it is possible to block the scapular nerve by eliciting a contraction of trapezium muscle and then injecting an additional 5 mL of local anesthetic. This is especially useful when the block is used to provide anesthesia for a shoulder arthroscopy, since a trocar is always placed posteriorly.
3. Sometimes it may be difficult to feel the interscalene groove at the C6 level. In these cases the groove can be more easily palpated distally immediately above the clavicle, where it is larger. Then the fingers can be progressively moved along the interscalene groove in the direction of C6.
Axillary Multistimulation Technique
Multistimulation techniques at the level of the axilla are based on the elicitation of motor responses associated with the stimulation of four nerves (the median, ulnar, radial, and musculocutaneous nerves). Accordingly, the muscular responses that need to be elicited are: (a) flexion of the fingers, induced by the stimulation of the median nerve; (b) extension of the fingers and especially the thumb, induced by the stimulation of the radial nerve; (c) flexion of the fourth and fifth fingers with opposition of the first finger, induced by stimulation of the ulnar nerve; (d) contraction of the biceps muscle with flexion of the forearm, induced by the stimulation of the musculocutaneous nerve (Fig. 9-1).
Patient Position: Supine, with the arm to be blocked abducted at 90° and the forearm flexed on the arm with another 90° angle while the head is slightly turned toward the contralateral side.
Needle Size: 22-gauge, 50-mm insulated needle.
Volume: 5 to 6 mL per nerve.
Anatomic Landmarks: At the level of the axilla, the axillary artery is surrounded by the median, radial, and ulnar nerves within the neurovascular sheath. The position of the nerves relative to the artery is variable. The musculocutaneous nerve leaves the axilla more proximally and enters the coracobrachialis muscle. The radial nerve is usually found posterior to the artery, the ulnar nerve lies on the inferior or posterior border of the artery, and the median nerve lies superior to the artery.
Approach and Technique: The axillary artery is identified and marked along with the inferior border of the major pectoralis muscle, and the coracobrachialis muscle. Then the insulated needle connected to a nerve stimulator (1.5 mA, 2 Hz, 0.1 ms) is introduced immediately above the axillary artery at a 45° angle as proximally as possible at the level of insertion of the long head of the biceps muscle (Fig. 9-1) in search of a stimulation of the median nerve (flexion of the fingers). After the proper stimulation is elicited, the position of the needle is adjusted to maintain the same motor response with a current of 0.5 mA. After negative aspiration for blood, 5 to 6 mL of the anesthetic solution is injected slowly. The needle is then withdrawn to the level of the skin and the intensity of stimulating current is set back to 1.5 mA. The needle is redirected toward the coracobrachialis muscle at 30° and deeper in search of a stimulation of the musculocutaneous nerve. After the proper stimulation is elicited, the position of the needle is adjusted to maintain the same motor response with a current of 0.5 mA. After negative aspiration for blood, 5 to 6 mL of the anesthetic solution is injected slowly. The needle is then withdrawn to the level of the skin, and the intensity of stimulating current is set back to 1.5 mA. The needle is reinserted through another skin puncture inferior to the axillary artery and perpendicular to the skin in search of the stimulation of the ulnar nerve (flexion of the fourth and fifth fingers with opposition of the first finger). The intensity of the current is progressively reduced to 0.5 mA. After a negative aspiration test, 5 to 6 mL of the local anesthetic solution is injected. The needle is withdrawn from the skin and then redirected posteriorly to the axillary artery in search of the radial nerve (extension of fingers including the thumb). After the proper stimulation is elicited, the position of the needle is adjusted to maintain the same motor response with a current of 0.5 mA. After negative aspiration for blood, 5 to 6 mL of the anesthetic solution is injected slowly.
Figure 9-1. An insulated needle connected to a nerve stimulator is introduced immediately above the axillary artery at a 45° angle as proximally as possible at the level of insertion of the long head of the biceps muscle in search of a stimulation of the median nerve.
1. Because of the variability of nerve distribution around the axillary artery it is important to not only have an appropriate knowledge of the possible anatomic variations but also the specific motor response associated with the stimulation of each nerve.
2. If the musculocutaneous nerve is first blocked, the needle needs to be redirected more superficially and proximal to the axillary in search of the median nerve. The median nerve is contained in the brachial plexus sheath. The musculocutaneous nerve exits early from this sheath.
3. The intercostobrachialis nerve, a branch of the T2 intercostal nerve, can be also blocked by subcutaneous injection of 5 mL of local anesthetic inferior to the axillary artery toward the inferior border of the axilla.
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