Charles A. Vacchiano and Andrew Biegner

Selection of Regional Anesthesia Techniques

When regional anesthesia is chosen for management of pain, the technique should be thoroughly discussed with the patient beforehand. The patient is informed of all optional procedures available, their potential risks, and their potential complications before an anesthesia technique is selected. Once this conversation takes place, the most appropriate anesthesia technique can be selected, and true informed consent can be obtained. Regional anesthesia is used extensively for surgical procedures involving the extremities or the lower abdomen, for the management of labor pain, for the management of obstetric procedures, and for the control of chronic pain syndromes. Frequently, regional anesthesia techniques are used in combination with other techniques to provide analgesia or anesthesia during surgical or obstetric procedures. Regional anesthesia may be the technique of choice when local anesthesia requires supplementation with heavy sedation. These techniques provide the patient with additional anesthesia options when selecting an anesthetic for surgical or obstetric procedures. It is the preferred technique for obstetrics and many other types of procedures.5–10

The administration of regional anesthesia to patients with a difficult airway or a full stomach presents both additional benefits and potential risks. The use of regional anesthesia, when appropriate, permits the patient to retain upper airway and pharyngeal reflexes while providing surgical anesthesia. Unless the sedation is reduced to a minimum, the airway may not be protected after the administration of the regional technique. Furthermore, block of the sympathetic nervous system theoretically results in increased gastric and intestinal motility, causing the stomach to empty sooner. However, this benefit may be negated by the perception of pain and anxiety that accompanies injury. If hypotension develops, the patient may have increased nausea and vomiting. When the block is instituted, the patient may lose consciousness as a result of the effects of alcohol if the patient is intoxicated at the time of treatment. At this point, airway support is required, and other problems may arise as well. Regional anesthesia should not be considered an alternative to securing the airway. If the patient’s airway cannot be secured in a safe manner in an emergent situation, use of a regional anesthetic should be avoided. The airway concerns must be addressed before the anesthetic technique is initiated so that the patient’s safety is maximized.¹¹

Complications of Regional Anesthesia

Complications of regional anesthesia can be immediate or delayed. Cardiovascular problems are the most critical immediate complications. However, effects on the respiratory and gastrointestinal (GI) systems can have equally serious consequences. Delayed complications include problems involving the cardiovascular, musculoskeletal, genitourinary, and neurologic systems.

Electrical Stimulators In Regional Anesthesia

Peripheral nerve stimulators are a valuable tool in the practice of regional anesthesia. Although ultrasound-guided blocks are becoming more common, nerve stimulator techniques may be used for select blocks or as an adjunct to an ultrasound technique. Often listed among the benefits of the use of a peripheral nerve stimulator are a reduction in the volume and dose of local anesthetic required to produce a block, increased success rate, and the ability to block nerves that are difficult to locate.

Electrical translocation devices provide a controlled stimulating pulse of variable amplitude that is administered through a conducting device. Location of neural fibers is improved without the need for eliciting repeated paresthesias. Specialized shielded needles have been designed to localize the distribution of the stimulating charge to the tip of the needle. This characteristic reduces confusion from wide-field stimulation of the area around the nerve, thereby enhancing the isolation of the appropriate nerve fibers.

The needle must be advanced slowly, and the amplitude of the unit must be adjusted as the needle approaches the nerve. The negative lead is attached to the skin with an electrocardiogram electrode, and the positive lead is attached to the needle. The electrical device must be equipped with an accurately adjustable amplitude from 0 to 5 mÅ with a digital readout of the amplitude.

When this technique is used, the stimulator should not be turned on until the needle has entered the skin. This measure reduces the discomfort experienced by the patient during the initial advancement of the needle. The patient must be instructed to identify discomfort verbally and to not move during the advancement of the needle.²⁹ Limiting the sedation helps the patient tolerate the procedure, maintain sufficient alertness to respond to the stimulus, and be cooperative.

Use of an electrotranslocation device can assist the practitioner during the administration of nerve block anesthesia to patients with sensory perception difficulties or neural degeneration, such as that experienced during end-stage renal disease. The use of an electrotranslocation device should not be restricted to brachial plexus techniques. Such a device can be used for enhancing any technique including ultrasound-guided nerve block, in which identification of specific nerve roots improves the success of the block and reduces the amount of medication required for anesthesia of the nerve root.

During a brachial plexus block, the stimulator is adjusted to deliver 2 mÅ after the needle has been introduced into the subcutaneous tissues. As the needle approaches the sheath, the amplitude is continuously reduced so that the muscle response to the stimulus is maintained. When the needle enters the sheath, the amplitude should be reduced to 0.5 mÅ. The muscle response to the stimulus continues to be the same as that obtained when the needle is outside of the sheath. The lower amplitude decreases the discomfort experienced by the patient while enhancing the ability to accurately identify the neurovascular bundle.

Patients may complain of aching or weakness along the path of the stimulated nerve after the regional anesthesia is terminated. This phenomenon is seen after the posterior tibial or the common peroneal nerves are stimulated. Severe or prolonged discomfort occurs when the stimulus is delivered over a long period or at a high current. The response to a stimulus with a lower amplitude is often adequate and results in less discomfort. Placement of the negative electrode has been important in the enhancement of electrotranslocation of the nerve. If the path of the nerve fiber is located under the negative electrode, a lesser stimulus produces a significant response.

Ultrasound-Guided Regional Anesthesia

The technology and clinical understanding of anatomic sonography has evolved greatly over the past decade. In anesthesia departments throughout the United States, ultrasound-guided regional anesthesia (UGRA) has become a routine technique and may become the “gold” standard for performing regional anesthetic nerve blocks.30–32 Direct visualization of the distribution of local anesthetics with high-frequency probes can improve the quality and avoid the complications of upper/lower extremity nerve blocks and neuroaxial techniques. Ultrasound guidance enables more accurate needle position and monitoring of the distribution of the local anesthetic in real time. The advantages over conventional guidance techniques, such as nerve stimulation and loss-of-resistance procedures, are significant. The key requirement for successful regional anesthetic block is to ensure optimal distribution of local anesthetic around nerve structures. This goal is most effectively achieved under sonographic visualization. Advantages of using ultrasound-guided techniques are noted in Box 45-3.^33,34 When compared with other forms of nerve localization, UGRA decreases performance time and onset time, and therefore decreases the time for surgical readiness from regional anesthesia. The quality of peripheral nerve block is also improved. To date, there are insufficient data to declare that UGRA improves overall block success. Whether UGRA improves safety has not been proven with large-scale randomized trials. Empirically, by allowing for the use of smaller volumes of local anesthetic as well as visualization of the real-time interaction of the needle, the nerve, and the local anesthetic, it appears the risk of LAST or neuronal toxicity will be reduced.^35,36 An interesting report noted that novice trainees learn the technique at variable rates but generally require 28 supervised trials before competency is achieved.³⁷

As noted previously, the key condition for a successful regional anesthetic block is the confirmation of an appropriate volume of local anesthetic around the targeted nerve structures. Proper placement of local anesthetic is most effective under ultrasound visualization. A medical ultrasound machine operates frequencies between 2 and 13 MHz. The average wavelength of an ultrasound beam is less than 1 mm. This limits the use of ultrasound technology to structures that are 1 mm in diameter or larger. In general, higher-frequency ultrasound probes (10-13 MHz) are best suited for visualizing structures less than 4 cm deep from the skin. For deeper structures, lower-frequency ultrasound probes (2-5 MHz) are more clinically useful. Nerve tissue that appears dark or hypoechoic appears dark because it does not reflect ultrasound waves. Nerve tissue appears white or hyperechoic because it does reflect ultrasound waves.

The handheld probe emits and collects the ultrasound waves in a fan-shaped beam, which is represented on the display screen in a two-dimensional plane. The on-screen vertical axis represents the distance an anatomic structure or block needle is from the ultrasound probe, whereas the horizontal axis represents the distance to the right or left of the center of the probe. Therefore, the ultrasound waves are used to construct an image of the “slice” of tissue centered on and beneath the ultrasound probe, much like a single image on a computed tomography (CT) scan.

The standard ultrasound image is rendered in shades ranging from white to black depending on the amount of energy that returns to the probe from structures being examined. Hyperechoic tissues reflect a large amount of the ultrasound waves back to the probe and therefore appear white. Hypoechoic tissues reflect fewer ultrasound waves and therefore appear as shades of gray. Anechoic areas do not reflect ultrasound waves and therefore appear black. The amount of reflection of ultrasound waves back to the probe is dependent on the amount of resistance to passage of the waves through a particular tissue. This characteristic is known as acoustic impedance. Differences in acoustic impedance at tissue interfaces results in the ability to identify specific anatomic structures. For example, bone has much greater acoustic impedance than soft tissue; therefore the interface between these two tissues will produce a hyperechoic image.³⁸

Needles used for regional anesthesia are echogenic but have very small cross-sectional areas. Therefore, the orientation of the needle with respect to the ultrasound beam affects the amount of sound energy reflected and hence the visibility of the needle on the screen. A needle oriented perpendicular to the ultrasound beam (i.e., “side on” to the beam) reflects a large amount of sound energy and is more easily visualized. In contrast, a needle that is parallel to the ultrasound beam (i.e., “end on” to the beam) reflects relatively little sound energy and is more difficult to visualize.

The orientation of the needle to the ultrasound probe during the administration of a regional anesthetic block is typically described in relationship to the image plane. The in-plane or axial/longitudinal approach allows the entire length of the needle (including the tip) to be visualized within the plane of the ultrasound image (Figure 45-1). In contrast, the out-of-plane, or tangential/short axis approach allows only the cross section of the needle to be visualized as a hyperechoic dot where it pierces the plane of the ultrasound image (Figure 45-2). The in-plane approach is favored when possible because it permits visualization of the entire length of the needle at all times; however, the anatomy associated with certain blocks may necessitate the use of the out-of-plane approach.

Upper-Extremity Block

Frequent injury of the hand, arm, and shoulder, combined with the accessibility of the nerves of the brachial plexus, has encouraged the development of regional anesthesia techniques for surgical procedures of the upper extremity, as well as the diagnosis and control of pain.³⁹ The widespread use of upper-extremity regional anesthesia is the result of numerous factors, including the availability of equipment to locate and deliver local anesthetics to the nerves of the plexus, the development of local anesthetics that can be applied alone and in combination to produce an appropriate duration of action for the procedure at hand, and the variety of techniques and approaches that can be used.

The four primary approaches for blocking the brachial plexus are axillary, interscalene, supraclavicular, and infraclavicular. Because of the ease of performance, the relatively high success rate and low incidence of complications, and the ability to produce anesthesia of the forearm and hand, the most frequently used technique is the axillary approach. The requirement for anesthesia of the upper arm and shoulder is most often met through use of the interscalene approach. This is because of the potential complications associated with needle placement in close proximity to the apex of the lung necessary with supraclavicular and infraclavicular block. The infraclavicular block is a safe and simple technique for providing surgical anesthesia of the lower arm, with an efficacy comparable to other approaches. The disadvantage is a higher risk of pneumothorax. Advantages of the infraclavicular approach include a lower likelihood of tourniquet pain and more reliable blockade of the musculocutaneous and axillary nerves when compared with a single-injection axillary block.40,41

The decision to use regional anesthesia rather than general anesthesia (which may be viewed by the surgeon as failure-free and more expedient) for elective and emergency surgical procedures of the upper extremity requires a strong commitment to and expertise in the use of these techniques. Moreover, the astute practitioner with experience and expertise in regional anesthesia does not lose sight of the fact that even in the most skilled hands, upper extremity block is associated with a degree of failure. In this regard, one can never rule out the potential requirement for conversion to general anesthesia and therefore must be cognizant of elements of the patient’s history and physical examination that would affect the ability to manage the airway and deliver general anesthesia safely.

Despite the fact that existing patient pathology may suggest a regional anesthetic, it is unwise to base the decision to use an upper extremity block (or any regional technique) solely on the premise that general anesthesia should be avoided, because ultimately, it may be unavoidable. The circumstances should dictate the degree to which “plan B” is considered and executed before administration of the block.

Brachial Plexus Anesthesia

Applied Anatomy of the Brachial Plexus

An understanding of brachial plexus anatomy is mandatory if effective clinical application of regional block techniques of the upper extremity is to be achieved. This includes familiarity with muscle, facial, and vascular anatomy in relation to the origin and distribution of the brachial plexus. However, intimate knowledge of many of the anatomic details with regard to the evolution of nerve roots distributed to the brachial plexus and ultimately to peripheral nerves is not clinically essential for successful blockade. The brachial plexus is a large network of nerves that extend from the neck through the axilla and innervate the upper extremity (Figure 45-3). It is composed of ventral rami, trunks, divisions, cords, and their branches. The supraclavicular portion of the plexus, including the five primary ventral rami and the three nerve trunks and their six divisions, lies in the posterior triangle of the neck. The infraclavicular portion of the plexus, including the three cords and their four terminal branches, lies in the axilla. These nerves combine, divide, recombine, and divide again as they pass between the anterior and middle scalene muscles, through the posterior triangle of the neck, and into the axilla, where they end in the four terminal branches that supply the upper extremity. The resulting nerve pathway, when pictured and contemplated in two dimensions and without the associated bone, muscle, and vascular structures, often leads to difficulty in understanding and applying this textbook anatomy in the clinical setting. When learning brachial plexus blockade, the value of augmenting written material with an apprenticeship at the hands of a master of the art cannot be overestimated.42–44

FIGURE 45-3 Derivation of the brachial plexus from the cervical spine. n., Nerve.

The archetypal brachial plexus is formed by the rami from the fifth (C5) to the eighth (C8) cervical nerves and the first thoracic (T1) nerve. In a small percentage of individuals, the fourth cervical (C4) or the second thoracic (T2) nerve or a combination of the two contributes to the plexus. After the rami pass the lateral border of the scalene muscles, they reorganize into trunks. The rami from C5 and C6 combine to form the superior or upper trunk, and the ramus from C7 continues alone as the middle trunk. The rami from C8 and T1 combine to form the inferior or lower trunk, which lies on the first rib posterior to the subclavian artery. The nerve trunks are enveloped by a fascial “sheath,” the origins of which are from the posterior fascia of the anterior scalene muscle and the anterior fascia of the middle scalene muscle. This forms a closed space at this level known as the interscalene space, or more generally as the sheath of the brachial plexus.

Cadaver studies have demonstrated the existence of extensive velamentous septa that can form compartments around the contents of this sheath. These septa appear to be incomplete and therefore may not function as mechanical barriers to the spread of local anesthetics. Indeed, a single injection of local anesthesia into this sheath commonly produces complete block of the upper extremity. Nevertheless, anatomic variations do exist, and it is possible that in certain individuals, septa occur that isolate nerves, resulting in so-called “patchy blocks” by preventing exposure to the injected local anesthetic. It has also been shown that injection even outside the sheath can produce neural blockade, albeit with a considerably greater latency period. The lesson to be learned with regard to clinical application of this information is that failure to allot a sufficient amount of time to perform an upper extremity block, and in particular to allow it to “set up,” generally produces an unsatisfactory result.42–44

At the lateral border of the first rib and posterior to the clavicle, each of the three trunks divides into ventral and dorsal divisions. These divisions are of significant clinical importance to application and evaluation of brachial plexus blockade, because the ventral divisions generally supply the ventral (flexor) portion of the upper extremity, and the dorsal divisions generally supply the dorsal (extensor) portions. As these divisions enter the axilla, the three posterior divisions combine to form the posterior cord, the anterior divisions of the superior and middle trunks combine to form the lateral cord, and the anterior division of the inferior trunk continues to become the medial cord. At that point, the cords are named according to their position in relation to the axillary artery. At the lateral border of the pectoralis minor muscle, each of these cords divides into two branches that reorganize to form the peripheral nerves of the upper extremity. The lateral cord divides and generates the musculocutaneous nerve and the lateral root of the median nerve. The medial cord divides and generates the ulnar nerve and the medial root of the median nerve. The posterior cord divides to generate the axillary and the radial nerves.

Understanding the anatomic relationships that result as the nerve cords give rise to the nerve branches and knowing the areas of the upper extremity these branches innervate are of paramount importance in the clinical application, evaluation, and supplementation of brachial plexus block. The branches of the lateral and medial cords (median, ulnar, and musculocutaneous nerves) predominantly supply the ventral portions of the upper extremity, and the branches of the posterior cord (radial and axillary nerve) predominantly supply the dorsal portions. However, in certain areas of the upper extremity, such as the posterior portion of the fingers and hand, there exists considerable cutaneous representation of the “predominantly ventral” median and ulnar nerves.

The radial nerve (C5 to C8 and Tl) is the major nerve supply to the dorsal extensor muscles, such as the triceps, of the upper limb below the shoulder. It supplies sensory innervation to the extensor region of the arm, forearm, and hand. The musculocutaneous nerve (C5 to C7) supplies the flexor muscles, such as the biceps, brachialis, and coracobrachialis, of the ventral portion of the arm. It supplies sensory innervation to the lateral aspect of the forearm between the wrist and elbow as the lateral antebrachial cutaneous nerve. The median and ulnar nerves pass through the arm and provide sensory and motor innervation to the forearm and hand. The median nerve (C6 to Tl) is better represented than the ulnar nerve in the forearm, where it supplies most of the flexor and pronator muscles. It also supplies sensory innervation to the ventral portion of the thumb, the first and second fingers, the lateral half of the third finger, and the palm of the hand. The ulnar nerve (C8 and Tl) is better represented than the median nerve in the hand, where it supplies motor innervation to most of the small flexor muscles. It has no sensory innervation of the forearm but supplies sensation to the medial part of the third finger, the entire fourth finger, and the remaining portion of the palm of the hand.

Approaches to Brachial Plexus Block

There are multiple approaches to local anesthetic block of the brachial plexus and various techniques applied with each approach. The choice of approach should be based on several factors, including patient considerations, the location of the planned surgical intervention, and especially the skill and experience of the anesthesia practitioner. Although surgical site and practitioner preference often drive the decision regarding which approach and technique are used, the patient’s body habitus, comfort, and coexisting disease and the nature and location of the injury are as important, if not more so, than these other concerns. Patient-related considerations should be weighed in the context of the risk of potential complications associated with a given approach, technique, and local anesthetic solution. The following discussion provides a practical approach to anesthesia of the brachial plexus, with a focus on axillary and interscalene approaches.⁴¹

Interscalene Approach

The interscalene approach to the brachial plexus was first described in 1970 by Dr. Alon Winnie. The interscalene approach is the most proximal brachial plexus block and is typically used to provide anesthesia for surgical procedures involving the shoulder and proximal humerus. It is the only technique that can provide adequate anesthesia and analgesia to the shoulder and the rest of the upper extremity. The catheter is placed at the level of the trunks, where the brachial plexus is relatively compact in size.⁴⁵ With the patient in the supine position, the anesthetist asks the patient to lower the shoulder on the side of the proposed anesthetic and surgery site to pull the shoulder away from the brachial plexus, intentionally trying to stretch the neck muscles and improve visualization and access. The patient’s head can then either be turned so that the patient looks away from the area of the anesthetic or moved laterally away from the site, maintaining forward vision.

The cricoid cartilage ring is then palpated just below the thyroid cartilage. This anatomic landmark correlates to the vertebral body of C6 and the corresponding area of the transverse process called Chassaignac’s tubercle. A straight line is drawn posteriorly to cross over the sternocleidomastoid (SCM) muscle, and the lateral border of the SCM is palpated. If this border is difficult to assess, the patient can be asked to raise the head against gentle resistance and then relax. Posterior to this border, the anesthetist palpates for the groove between the anterior and middle scalene muscles with two fingers (Figure 45-4). This is the level of the trunks of the brachial plexus (Figure 45-5).

FIGURE 45-4 Technique for identifying the anterior and middle scalene muscles and the major vessels so the interscalene perivascular technique can be accomplished. m., Muscle.

FIGURE 45-5 Three trunks of the cervical plexus are revealed lying alongside the subclavian vessels. m., Muscle.

After cleansing the patient’s skin, an intradermal skin wheal of local anesthetic is made at this point on the groove. A 22-gauge, insulated B-bevel needle, usually 1½ inches long, is inserted gently through the skin wheal perpendicularly to the skin and then angled slightly caudad. The needle is attached to an intravenous extension tube with an anesthetic-filled syringe. The patient is told what to expect, and the needle is slowly advanced until a motor twitch response is elicited. The nerve stimulator current is lowered from 1 to 0.5 mÅ to minimize excessive current to the patient and to ensure proper needle position. After gentle aspiration is negative for blood or CSF, a test dose of 1 mL of local anesthetic solution is injected. A fade will be observed in the quality of the motor twitch experienced by the patient. This indicates that the needle is probably within the brachial plexus sheath. If no subjective symptoms of toxicity reaction are present, incremental injections of 3 to 5 mL of local anesthetic, each followed by aspiration to detect blood, are administered until the intended volume is given. In adult patients, the volume is usually 30 to 35 mL.41,46

Ultrasound-Guided Interscalene Block:

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