Nerve Blocks

Fig. 9.1

Sterile dressing and ultrasound probe

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Control syringe used for hand-on-syringe technique

../images/323313_1_En_9_Chapter/323313_1_En_9_Fig3_HTML.jpg — Fig. 9.3

Hand-on-needle technique

We recommend establishing a specific location in your setting, be it an emergency department (ED), office, clinic, intensive care unit, or other with dedicated to nerve block supplies. This simple step will reduce time needed to prepare for the ultrasound-guided nerve blocks as well as ensure all essential items are present during the procedure.

The two local anesthetics typically stocked in a variety of clinical settings are lidocaine and bupivacaine. Both can be used for peripheral nerve blocks. For the novice provider, lidocaine is preferred over bupivacaine. Inadvertent vascular deposition of anesthetic can occur even with meticulous methods. Bupivacaine is known to be toxic to the cardiac and central nervous systems, and we recommend that providers who are not very comfortable with the subtle nuances of needle tip visualization only use lidocaine with or without epinephrine. Lidocaine has vasodilatory effects, and thus epinephrine will extend the duration of the analgesia. Even with lidocaine’s shorter half-life and increased safety profile, the provider should be familiar with the signs and symptoms of local anesthetic systemic toxicity (LAST) . Classically, the patient will complain of tongue numbness and light-headedness, which then progresses to muscle twitching, unconsciousness, seizures, and cardiovascular depression [6]. If bupivacaine has been inadvertently injected into the vascular system, the use of a hyperlipophilic solution (20% Intralipid; 1.5 mg/kg bolus with continued infusion of 0.25 ml/min) should be infused. We recommend 20% Intralipid be readily available when performing an ultrasound-guided peripheral nerve block. Standard safety techniques dictate the provider never injects without ultrasonographic visualization of the needle tip and always aspirates before injecting to confirm lack of vascular puncture.

Locating nerves with ultrasound requires knowledge of adjacent anatomical landmarks. Typically, nerves course through the body adjacent to fascial planes and vascular structures. Nerves are best visualized and targeted for blocks when oriented in cross section. There are subtle differences of nerve appearance based on anatomic location. Distal peripheral nerves appear on ultrasound as bundles of hyperechoic circles or “cluster of grapes” or having a “honeycombed” quality (Fig. 9.4). Employing the use of anisotropy to identify nerves is important. Anisotropy is a sonographic artifact defined as being directionally dependent. Nerves inherently have a significant amount of anisotropy. Thus, when the ultrasound probe is directly perpendicular to the nerve axis, it will appear very bright; however, when you angle or rock the transducer back and forth, the nerve will become darker and less discernible (Fig. 9.5). Proximal peripheral nerves, such as the roots of the brachial plexus, appear as individual anechoic circles that can easily be mistaken for blood vessels (Fig. 9.6). Subtle fanning of the transducer may be necessary to minimize the effects of the anisotropy and obtain the highest-quality images. We recommend that novice sonographers verify with color Doppler that the intended target is not vasculature.

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Ultrasound image of peripheral nerve described as “honeycombed” or “cluster of grapes”

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An example of anisotropy: (a) probe perpendicular to nerve displaying bright, hyperechoic nerve and (b) probe angled away from perpendicular orientation illustrating darker, less hyperechoic nerve

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Ultrasound image of proximal nerve bundle that can resemble vascular structures

There are two standard needle orientations one can employ to safely place the needle tip adjacent to the nerve.

In-plane needle visualization technique

The needle is inserted lateral and parallel to the long axis of the transducer (Fig. 9.7). As the needle passes under the transducer, the entire length of the needle will be visualized (Fig. 9.8). The trajectory of the needle must be midline and parallel to the transducer in order to visualize the needle in its entirety. The in-plane technique for needle tip visualization is recommended for novice sonographers performing peripheral nerve blocks.

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Appropriate placement for in-plane needle visualization technique with needle positioned parallel to the long axis of the ultrasound probe. (a–c) All examples of in-plane needle visualization procedures

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Ultrasound image showing appropriate in-plane needle visualization technique with the entire needle visualized

Out-of-plane needle visualization technique

The needle is inserted midline and perpendicular to the long axis of the transducer at a steep angle (greater than 70°–80°) to the skin (Fig. 9.9). The needle tip will only be visualized as a hyperechoic dot as it passes under the transducer (Fig. 9.10). Safe and successful execution of this technique relies on confident visualization of the needle tip, which requires strong spatial motor skills with both the probe and the needle.

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Appropriate needle placement for out-of-plane needle visualization technique with needle positioned midline and perpendicular to the long axis of the ultrasound probe (a–c)

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Ultrasound image showing appropriate out-of-plane needle visualization technique with the hyperechoic needle tip visualized

There are two standard needle/syringe combinations to perform a successful peripheral nerve block.

Hand-on-syringe technique

This is a single-operator technique. The provider attaches the needle typically onto a 10-ml control syringe. In this technique, the operator then is in control of the needle, aspiration, and injection of the anesthetic. The operator can appreciate the tactile feedback of this single-operator approach.

Hand-on-needle technique

This is a two-person technique. The chosen needle is attached to IV tubing which is attached to the anesthetic-filled syringe. The provider holds the needle directly onto the skin surface and when in the appropriate position instructs a second operator to aspirate and then inject the local anesthetic.

It has yet to be determined which needle technique is preferred [7]. While the hand-on-needle technique affords the operator more precise needle targeting, the operator loses the tactile feedback of aspiration and injection. Furthermore, the hand-on-needle technique requires two operators to perform, and, in a busy ED setting, the hand-on-syringe technique can be performed by one operator, which might be preferred.

Post-peripheral nerve block care is extremely important. You have intentionally anesthetized part if not all of an extremity. The anesthetized extremity should be labeled with indelible marker describing the type of block performed as well as the date and time of the block completion. Nursing should be alerted that the patient has had a peripheral nerve block. Appropriate care should be applied to the extremity including appropriate padding and positioning, splinting, and ice if necessary. Consultants should also be aware that the block was performed and communicate the local anesthetic used and the expected duration of the block.

Advantages of Ultrasound Guidance

Ultrasound guidance offers many potential benefits to peripheral nerve blockade in the acute care settings. It eliminates the need for multiple needle insertions and redirections that can prolong procedure times and subject the patient to unnecessary pain and injury during peripheral nerve blockade. Specifically, ultrasound allows the operator to see target nerves, advance the needle under real-time visualization, and monitor the spread of local anesthetic. Ultrasound allows visualization of not only the nerves but other adjacent vital structures (arteries, veins, tendons, etc.) and reduces the incidence of inadvertent puncture of these structures. It avoids the unintentional injection of local anesthetic into the vasculature and minimizes the chance of local anesthetic toxicity. Overall, real-time ultrasound guidance reduces the risks of neuropathy from intraneuronal injection, systemic toxicity due to accidental intravascular injection, and other complications, such as pneumothorax, visceral injury, etc. [1]. The ability to visualize both anatomical structures and the needle under ultrasound guidance improves operator accuracy during the infiltration of anesthetic solution, which in turn leads to faster onset time, increased success rate, and reduced procedure time [1, 2]. The volume of local anesthetic required to achieve the anesthesia is considerably less than that required when using traditional landmark techniques since the operator can see the spread of local anesthetic around a nerve and can adjust the needle tip position as necessary to optimize local anesthetic distribution [1–3]. Unlike procedural sedation, ultrasound-guided nerve blocks do not require additional staff or prolonged post-procedure observation period. Ultrasound-guided nerve blocks have been shown to decrease length of stay, reduce hospital costs, and improve patient satisfaction [1–3].

Blocking the Brachial Plexus: Ultrasound-Guided Interscalene and Supraclavicular Nerve Block

The brachial plexus provides the complete motor and sensory innervation to the upper extremity. The brachial plexus includes the nerve roots of C5–T1. These nerve roots leave the cervical spine just posterior to the musculature of the neck and join with the subclavian artery and vein before entering into the upper extremity. The brachial plexus can be blocked in various locations, with this decision based on both a simple ultrasonographic anatomic surveillance and the specific injury that needs to be addressed. As the brachial plexus travels from the spinal column toward the upper extremity, the interscalene groove in the neck and just lateral to the subclavian artery in the supraclavicular fossa has been the most popular locations for regional anesthesia. The interscalene brachial plexus block will most consistently block the nerve roots of C5–C7 making this a useful choice for injuries more proximal to the mid-humerus. The supraclavicular brachial plexus block will most consistently provide analgesia for injuries from the mid-humerus to the hand. This is a simplified assumption for novice providers; in actuality the innervation of the wrist and hand is extremely complex.

Ultrasound-Guided Interscalene Nerve Block

Anatomy

The interscalene block is performed at the interscalene groove formed by the anterior and middle scalene muscles. The interscalene groove is located just below the clavicular head of the sternocleidomastoid muscle at the level of the cricoid cartilage. The medial border is the anterior scalene muscle. The lateral border is the middle scalene muscle. The C5–C7 nerve roots are quite superficial and lie between the anterior and middle scalene muscles of the neck. The C8 and T1 nerve roots are deeper and more difficult to visualize consistently. Landmarks to identify include the carotid artery and internal jugular vein medial to the anterior scalene muscle. The pleural line lies more caudal and should not be at risk of puncture if the block is done at the appropriate location, and clear ultrasonographic needle tip visualization is maintained during the procedure.

Indications

The interscalene block consistently provides anesthesia to the proximal upper extremity including the shoulder and proximal humerus. Typically, this block should be performed for pain control in patients with injuries of the proximal upper extremity (burns, proximal humeral fractures, etc.). The interscalene brachial plexus block is also ideal as either an adjunct or alternative to procedural sedation for large upper-arm laceration repairs, abscess incision and drainage, and glenohumeral reductions.

Contraindications

The interscalene block will almost always cause transient, ipsilateral diaphragm paralysis due to the fascial spread of local anesthetic over the anterior scalene muscle – anesthetizing the phrenic nerve [8]. In healthy patients without pulmonary dysfunction, the debate persists about the clinical significance of ipsilateral phrenic nerve paralysis. Ultrasound guidance has increased needle precision and lowered the amount of anesthetic volume needed to achieve a successful block, theoretically reducing the phrenic nerve paralysis [9]. We caution the use of the interscalene block in patients with poor pulmonary reserve, such as patients with severe COPD, restrictive lung disease, and severe obstructive sleep apnea. Also, the sympathetic afferent chain or recurrent laryngeal nerve can incidentally be anesthetized. This will rarely cause a temporary Horner’s syndrome (ptosis, miosis, and anhydrosis) or a temporary hoarse voice. Also, the interscalene block should not be done on a patient with known contralateral laryngeal nerve palsy. Like previously mentioned for all ultrasound-guided nerve blocks, we do not recommend performing this procedure in patients with a risk for vascular injury, preexisting neurologic injury, or high risk for compartment syndrome.

Equipment/Probe Selection

A high-frequency linear probe should be used for the interscalene block. A 20–22-gauge 3.5-inch/9-cm spinal needle will be needed in most patients. Standard nerve block materials should be used and are discussed in the introduction section.

Preparation/Pre-procedural Evaluation

The patient should be placed on a cardiac monitor and positioned upright or in a semi-reclining position with the head rotated 30° away from the affected side. The ultrasound system should be placed on the opposite side of the block for easy visualization during needle manipulation. Since the interscalene block is quite superficial and will be performed in plane, place the patient in a mild decubitus position. This allows the operator a flat approach to the interscalene groove and maximize needle visualization during the entire block.

A survey scan should be performed. First, place the high-frequency linear probe in a transverse orientation on the neck of the affected side at the level of the cricoid (Fig. 9.11). Second, locate the carotid artery and internal jugular vein, and slowly slide the probe laterally until the superficial head of the sternocleidomastoid (SCM) muscle is visualized (Fig. 9.12). Third, identify the anterior and middle scalene muscles just deep to the SCM muscle. The anterior scalene muscle is the medial border of the interscalene groove, and the middle scalene muscles are the lateral border. Fourth, identify the roots of the brachial plexus that lie between the anterior and middle scalene muscles. At the interscalene groove, the C5–C7 roots of the brachial plexus are superficially wedged together and are hypoechoic round or ovoid structures vertically aligned, colloquially coined as the “traffic light” sign. The C8 and T1 nerve roots may be sonographically visualized as well; however, they lie deeper. We recommend that the clinician use color Doppler to ensure that the anechoic nerve roots are not vascular structures and that the needle path will not traverse unforeseen veins and/or arteries. Clinicians using color Doppler should be comfortable with manipulation of specific parameters (e.g., pulse repetition frequency) to ensure that the vasculature with minimal flow will be detected.

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Appropriate patient and probe positioning for interscalene nerve block

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Appropriate ultrasound probe placement for interscalene nerve block. (a) Identifying the carotid (CA) and internal jugular vein (IJV) and (b) sliding lateral to identify sternocleidomastoid (SCM), anterior scalene (AS), and middle scalene (MS) muscle with brachial plexus (BP) between scalene muscles

Oftentimes visualization of the nerve roots can be challenging at this level by simply sliding the ultrasound probe laterally in the neck at the level of the cricoid. The alternative approach involves identification of the brachial plexus in the supraclavicular fossa and then moving proximally to the interscalene groove. For this approach, first, place the transducer parallel to the clavicle in the supraclavicular fossa (Fig. 9.13). Second, aim the transducer caudally until you can visualize the subclavian artery in cross section. Third, visualize brachial plexus located laterally to the subclavian artery. Sonographically, the brachial plexus at this level will appear as a “cluster of grapes” or “honeycombed.” Fourth, follow the brachial plexus in a cephalad pathway up the neck until you see the nerve roots orient in the “stop light” pattern in the interscalene groove with the medial and lateral borders of the anterior and middle scalene muscles, respectively.

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Alternative initial placement of ultrasound probe for interscalene nerve block in the (a) supraclavicular fossa just above the clavicle (dotted line) identifying the subclavian artery (SCA) with the underlying rib and lung pleura and then lateral the brachial plexus (BP) and then (b) moving the probe cephalad to the interscalene groove to identify the brachial plexus (BP) adjacent to the anterior (AS) and middle (MS) scalene muscles with the internal jugular vein (IJV) medially and the sternocleidomastoid (SCM) above

Procedure

We recommend novice providers perform the interscalene brachial plexus in plane with a lateral-to-medial approach. A small skin wheal should be placed just lateral to the ultrasound probe. A 20–22-gauge 3.5-inch needle is inserted just lateral in the same direction as the transducer (in-plane technique) (Fig. 9.14). The needle tip should be clearly visualized and slowly advanced through the middle scalene muscle to the lateral border of the interscalene groove. We recommend depositing 1–2-ml aliquots slowly until the 10–20 ml is delivered. The clinician should always aspirate before placing anesthetic to ensure lack of vascular puncture as well as clearly visualize anechoic anesthetic spread on the ultrasound screen. If the needle tip is in the appropriate location, local anesthetic will track along the fascial plane between the middle scalene muscle and the nerve roots in the interscalene grove. Classically, a successful block is visualization of the “donut sign” described as hypoechoic anesthetic surrounding the brachial plexus. However, placement of the needle tip in the potential space between the brachial plexus sheath and middle scalene is often adequate for a successful block, and the “donut sign” is not necessary [10].

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(a) Correct needle and ultrasound placement for the interscalene nerve block and then (b) in-plane ultrasound needle placement in the potential space between the middle scalene muscle and brachial plexus

Complications

The ultrasound-guided brachial plexus block at the interscalene groove can be learned and performed successfully even with the close proximity of adjacent vascular structures, nerve bundles, and lung apices. Once the in-plane technique is mastered, ultrasound guidance affords precise needle tip localization and reduced anesthetic volume requirements, making the procedure relatively safe. Uncommon complications include transient phrenic nerve paralysis that causes respiratory compromise, pneumothorax, and inadvertent vascular puncture. Because of the close proximity of the phrenic nerve (medial aspect of the anterior scalene muscle), caution should be taken when performing the interscalene brachial plexus block on patients with poor pulmonary reserve. Also, the sympathetic chain can incidentally be blocked causing a temporary Horner’s syndrome. The best approach to prevent sympathetic chain injury is the injection of low volumes of anesthetic with the needle tip under the fascial plane however far from the nerve bundle. Iatrogenic pneumothorax is a theoretical risk; however, if performed at the level of the larynx and clear needle tip visualization is maintained, lung puncture will not occur. Lastly, the transverse cervical artery typically runs laterally and caudal to the brachial plexus in the interscalene groove. Rarely, this artery can course through the brachial plexus. Once you identify the interscalene groove and the brachial plexus, color Doppler should be performed to ensure this artery does not course through the brachial plexus. If the artery is present in the brachial plexus, you should not perform the block in the interscalene groove.

Pearls/Pitfalls

The ultrasound-guided interscalene nerve block will not consistently block the C8 and T1 nerve roots so that injuries to the mid/distal humerus, elbow, forearm, wrist, and hand will not achieve consistent anesthesia. For distal upper-extremity injuries, we recommend the supraclavicular brachial plexus block.

Integration into Clinical Practice

The ultrasound-guided interscalene nerve block is an excellent block for proximal upper-extremity injuries including shoulder/deltoid burns, lacerations, shoulder dislocations, and proximal humerus fractures.

Evidence

In 2008, Dr. Stone et al., in a small prospective study, showed that interscalene block decreased length of stay when compared to procedural sedation for upper-extremity emergencies [11]. Furthermore, in 2012, a study done by Dr. Blaivas et al. determined an interscalene block decreased length of stay in patients with shoulder dislocation compared to procedural sedation [12].

Key Points

Interscalene blockade is useful for procedures around the shoulder and upper arm.
The lateral-to-medial insertion is often chosen to prevent injury to the phrenic nerve, which is typically located anteriorly to the anterior scalene.
Caution should be taken with patients with pulmonary dysfunction as the interscalene block causes ipsilateral phrenic nerve paralysis.