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Brachial Plexus Block
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The brachial plexus innervates the entire upper extremity. Blockade of the brachial plexus can be performed to repair tendons or extensive lacerations, to reduce fractures and dislocations, or to provide anesthesia for burn care, to name a few uses. Protect the arm from injury if this procedure is to be performed by properly supporting the arm, padding the ulnar nerve and pressure points, and not extending or displacing the arm posteriorly.
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The brachial plexus arises from the C5 to T1 nerve roots (Figure 126-15). The nerve roots fuse to form three trunks. Each trunk divides into an anterior and posterior division that then redistributes to form the lateral, medial, and posterior cords. These cords divide in the region of the axilla to form the musculocutaneous nerve, the median nerve, the ulnar nerve, the axillary nerve, the radial nerve, and several cutaneous nerves. The brachial plexus crosses the midclavicle to enter the axilla (Figure 126-16A).
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The brachial plexus may be blocked from the supraclavicular, interscalene, infraclavicular, or axillary approach. The preferred method for the Emergency Physician is the axillary block.
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Brachial Plexus Block, Supraclavicular Approach
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The anatomy of the brachial plexus is described above. This approach blocks the brachial plexus at the level of the trunks, where it is most compactly arranged.
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Place the patient supine with their head turned 45° from the midline and toward the side opposite that being anesthetized (Figure 126-16A). Place the ipsilateral arm in any position of comfort for the patient.
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The subclavian artery is the main landmark. Palpate the subclavian artery immediately lateral to the clavicular head of the sternocleidomastoid muscle in the interscalene groove. Identify the midpoint of the clavicle.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution 2 cm above the midclavicle. Insert a 25 gauge needle directed caudally through the skin wheal (Figures 126-16B & C). Advance the needle until the patient experiences paresthesias. Withdraw the needle 1 mm and allow the paresthesias to resolve. Aspirate to ensure that the tip of the needle is not within a blood vessel. Inject 40 mL of local anesthetic solution. Reduce the volume based upon the patient's body size and the maximal allowable dose to prevent toxicity.
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Place the US probe in an oblique coronal plane above the clavicle and lateral to the sternocleidomastoid muscle (Figure 126-16D). Locate the subclavian artery. It is a pulsatile, round, and hypoechoic structure in cross section. The trunks of the brachial plexus are located adjacent to the subclavian artery (Figure 126-16E). Posterior to the subclavian artery lies the first rib, and the pleural line can be seen sliding in real time. Use color/power Doppler to confirm the location of the subclavian artery and any branches or take-offs, all of which must be avoided (Figure 126-16F). Anesthetize the skin. Position the spinal needle lateral to the US probe and parallel to its long axis. Slowly insert and advance the needle. Visualize the entire length of the needle as it is introduced through the subcutaneous tissue toward the brachial plexus. Advance the needle through the nerve sheath. Aspirate to ensure the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of anesthetic around the nerves. If it is satisfactory, inject the remainder of the local anesthetic solution to achieve the “donut sign” (Figure 126-16G). If the test dose is not satisfactory, reposition the needle and inject another test dose.
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This block is characterized by a quick onset of anesthesia and a complete block. A high volume of anesthetic is required with a quick onset of anesthesia. There is no chance of missing peripheral or proximal nerve branches because of failure of the local anesthetic solution to spread along the sheath of the brachial plexus. Unfortunately, this technique is difficult to teach and to master without considerable experience. This technique has a high incidence of an iatrogenic pneumothorax, reportedly up to 6%. Other complications include blockade of the phrenic nerve, subclavian artery puncture, and Horner's syndrome. Unintentional intravascular injection can result in high blood levels of the local anesthetic agent.
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Brachial Plexus Block, Interscalene Approach
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The anatomy of the brachial plexus is described above. This approach blocks the brachial plexus at the level of the trunks (Figure 126-17A).
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Place the patient supine with their head turned 45° from midline and toward the side opposite that being anesthetized (Figure 126-17A). Place the ipsilateral arm in any position of comfort for the patient.
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Identify the posterior border of the clavicular head of the sternocleidomastoid muscle by palpation. Move the palpating finger laterally until it rolls into the interscalene groove between the anterior and middle scalene muscles, at the level of the cricoid cartilage (Figure 126-17B).
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution in the interscalene groove, at the level of the cricoid cartilage. Slowly insert a 25 gauge needle through the skin wheal in a dorsal, medial, and caudal direction (Figure 126-17B). Advance the needle until the patient experiences paresthesias. Withdraw the needle 1 mm and allow the paresthesias to resolve. Aspirate to ensure that the tip of the needle is not within a blood vessel. Inject 30 to 40 mL of local anesthetic solution. Reduce the volume based upon the patient's body size and the maximal allowable dose to prevent toxicity.
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This block is performed at the level of the internal jugular vein and carotid artery in the neck. Place the US probe on the neck, less than a third of the way up from the clavicle (Figure 126-17C). Identify the carotid artery and internal jugular vein. Move the US probe laterally to find the muscle bellies of the anterior and middle scalene muscles (Figure 126-17D). Between the muscles lie the nerve roots of the brachial plexus in cross section. It is represented by hypoechoic circles within the hyperechoic rings of the nerve sheaths (Figure 126-17D). Use color Doppler to identify any blood vessels in the field, and note their location so as to avoid them. Anesthetize the skin. Using a posterior approach, insert the spinal needle connected by extension tubing to a 20 mL syringe filled with local anesthetic solution. Advance the needle and visualize it approaching the brachial plexus. The needle path will usually go through the middle scalene muscle. Once the brachial plexus is close to the needle tip, use a short and controlled jab to penetrate through the nerve sheath. Aspirate to verify that the needle tip is not in a blood vessel. Instruct an assistant to deliver a test dose of 1 to 2 mL of local anesthetic solution. If the anesthetic spreads around the nerves, slowly deliver the remainder of the local anesthetic solution to obtain the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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The advantages and disadvantages are similar to those of the supraclavicular approach with the exception of possibly not achieving anesthesia of the lower trunk. This may require supplementary blockade of the median and ulnar nerves. The interscalene brachial plexus block, although ideal for regional anesthesia of the shoulder, has been associated with recurrent laryngeal nerve paralysis and an almost 100% incidence of phrenic nerve paralysis.20 This can be significant in patients with respiratory comorbidities (e.g., COPD, obesity).21 The supraclavicular brachial plexus block is associated with lower rates of these complications.2
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Brachial Plexus Block, Axillary Approach
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The anatomy of the axillary brachial plexus nerve block is rather simple. The neurovascular bundle is easily found at the anterior axillary fold by palpating for the pulsations of the axillary artery. The neurovascular bundle is surrounded by the fibrous axillary sheath (Figure 126-18A). The axillary sheath is bound medially by skin and connective tissue, anteriorly by the biceps and coracobrachialis muscles, inferiorly by the triceps muscle, and laterally by the neck of the humerus. The axillary artery is the central reference structure within the neurovascular bundle. Within the axillary sheath, the median nerve is anterior, the radial nerve is posterolateral, and the ulnar nerve is posterior to the axillary artery. The axillary vein is medial to the artery. The medial antebrachial cutaneous nerve and the medial brachial cutaneous nerve are medial to the artery (Figure 126-18A). The only sensory nerve outside the neurovascular bundle is the musculocutaneous nerve. This nerve exits the axillary sheath as it crosses the clavicle.
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Place the patient supine with their head turned toward the side opposite that being anesthetized (Figure 126-18B). Abduct the arm 90°. Flex the elbow 90° so that the forearm is parallel to the long axis of the body and the palm is facing upward.
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Identify the brachial artery by its palpable pulse. Trace it proximally to the anterior axillary fold, formed by the pectoralis major muscle. Use the index and middle fingers of the nondominant hand to secure the neurovascular bundle (identified by the pulse) against the humerus (Figure 126-18B).
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Needle Insertion and Direction
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Place the skin wheal of local anesthetic solution overlying the axillary artery pulse, just posterior to the anterior axillary fold. Insert a 22 gauge spinal needle just above the fingertip on the axillary pulse, directed toward the apex of the axilla and in the direction of the neurovascular bundle (Figure 126-18B). Advance the needle. A “pop” will be felt as the axillary sheath is penetrated. The correct needle position is confirmed by eliciting paresthesias, observing blood flow in the needle, or observing pulsations of the needle that match the pulse (Figure 126-18C). Instruct an assistant to attach the distal end of intravenous extension tubing to the hub of the needle, and the proximal end to a 60 mL syringe containing local anesthetic solution. The Emergency Physician must always maintain pressure against the neurovascular bundle with the nondominant hand while stabilizing the needle with the dominant hand. Instruct the assistant to aspirate to ensure that the tip of the needle is not within a blood vessel. Withdraw the needle 2 mm if blood flow or paresthesias are elicited.
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Apply digital pressure to the neurovascular bundle just distal to the tip of the needle with the nondominant fingers. This prevents the local anesthetic solution from flowing distally. Inject the local anesthetic solution into the axillary sheath after the paresthesias have resolved and a negative aspiration has been achieved. Instruct the assistant to inject a volume of approximately 40 mL in the adult patient. This volume has been shown to consistently block the entire brachial plexus. Reduce the volume based upon the patient's body size and the maximal allowable dose to prevent toxicity. Continue to apply digital pressure to the neurovascular bundle just distal to the needle during and after injection of the local anesthetic solution.
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Withdraw the needle while the assistant simultaneously injects 3 to 5 mL of local anesthetic solution into the subcutaneous tissue. This blocks the medial brachial cutaneous nerve and the intercostobrachial nerve. Abduct the patient's arm 30° to 45° after the needle is withdrawn. Maintain this position, while continuing to apply digital pressure to the neurovascular bundle just distal to the needle insertion site, for 2 to 3 minutes.
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This block is performed at the level of the terminal branches of the brachial plexus within the axillary sheath. These branches are visualized as hyperechoic nodules around the pulsatile and hypoechoic axillary artery (Figures 126-18D & E). Place the US probe with the marker pointing cephalad at the superior axillary crease (Figure 126-18F). Locate the axillary artery and vein in cross section (Figure 126-18G). The musculocutaneous nerve can be seen between the biceps muscle and the coracobrachialis muscle. Use color Doppler to confirm the location of the axillary artery, vein, and any branches or take-offs (Figure 126-18G). Anesthetize the skin. Position the spinal needle inferior or superior to the long axis of the US probe (Figure 126-18F). Slowly insert and advance the needle. Visualize the entire length of the needle as it is advanced. Aim the needle between the axillary artery and vein. Advance through the nerve sheath. Aspirate to ensure the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of local anesthetic solution around the subclavian artery. If it is satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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The axillary approach to the brachial plexus is the most commonly used and preferred technique. The procedure is easily mastered, has no major complications, and is easily performed in the obese patient. The disadvantages of this technique include insufficient anesthesia of the shoulder and upper arm. The musculocutaneous nerve provides sensory innervation to the radial aspect of the forearm and may be missed by the local anesthetic agent. The subcutaneous infiltration of local anesthetic solution usually blocks the musculocutaneous nerve. Proximal flow of the local anesthetic solution is required to ensure adequate anesthesia. Abduction of the arm while maintaining pressure on the neurovascular bundle allows proximal flow of the local anesthetic solution. It also prevents the humeral head from limiting proximal spread due to compression of the brachial plexus.
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Brachial Plexus Block, Infraclavicular Approach
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This approach to the brachial plexus has many advantages and few serious complications. Unfortunately, this technique requires considerable experience on the part of the Emergency Physician and a nerve stimulator to locate the brachial plexus (Figures 126-19A & B). For these reasons, the anatomic landmark approach will not be described. The US-guided technique is described below.
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The anatomy of the brachial plexus is described above. This approach blocks the brachial plexus at the level of the cords (Figure 126-15A).
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Place the patient supine with their head turned 45° from midline and toward the side opposite that being anesthetized (Figure 126-19A). Place the ipsilateral arm extended 90°.
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Identify the middle third of the clavicle.
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Infraclavicular Block
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This block is performed below the clavicle. The cords of the brachial plexus lie below the pectoralis major and minor muscles. They appear as distinct hyperechoic nodules positioned laterally, medially, and posteriorly around the subclavian artery (Figures 126-19C & D). Prep and drape the infraclavicular region. Place the US probe with the marker pointing cephalad below the clavicle, medial to the coracoid process (Figure 126-19E). Locate the subclavian artery (which is pulsatile) and vein in cross section. Use color Doppler to confirm the location of the subclavian artery, vein, and any branches or take-offs (Figure 126-19F). Anesthetize the skin. Position the spinal needle inferior or superior to the long axis of the US probe (Figure 126-19E). Insert and advance the needle. Visualize the entire length of the needle as it is advanced. Aim the needle between the subclavian artery and vein. Advance the needle. Continue to advance the needle through the nerve sheath. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of local anesthetic solution around the subclavian artery. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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This block can result in an iatrogenic pneumothorax due to the proximity of the needle to the lung apex.
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Median Nerve Block at the Elbow
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The median nerve innervates all the muscles of the anterior forearm except the flexor digitorum profundus to the ring and little fingers and the flexor carpi ulnaris.12,22,23 It innervates the thenar muscles and the lumbrical muscles to the index and middle fingers in the hand. It provides sensory innervation to the palmar aspect of the thumb, index finger, middle finger, radial portion of the ring finger, and the lateral half of the palm (Figure 126-20A). The median nerve provides a variable amount of sensory innervation to the dorsal distal surfaces of the lateral three and one-half fingers.12
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Place the patient supine with their arm abducted 45°, the elbow in full extension, and the hand supinated (Figure 126-21A).
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Identify the medial and lateral epicondyle of the humerus by palpation. Connect the epicondyles with a straight line (Figure 126-21A). Identify the brachial artery by palpating for its pulse just medial to the biceps tendon and over the line just drawn. Mark the site of the palpable pulse with a marker.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution just medial to the pulse, at the level of the intercondylar line. Insert a 25 gauge needle perpendicular to the skin and slowly advance it. If paresthesias are elicited, withdraw the needle 1 to 2 mm and allow the paresthesias to resolve. Inject 3 to 5 mL of local anesthetic solution. If paresthesias are not elicited, slowly move the needle in a fan-like pattern to elicit paresthesias. Withdraw the needle 1 to 2 mm, allow the paresthesias to resolve, and inject 3 to 5 mL of local anesthetic solution.
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Place the US probe in the crease of the antecubital fossa. Locate the pulsatile brachial artery in the middle of the antecubital fossa (Figure 126-21B). Anesthetize the skin medial to the brachial artery. Place the spinal needle inferior to the short axis of the US probe directly over the median nerve, which should be medial to the brachial artery. Only the tip of the needle will be visualized in this view. Insert and advance the needle until its tip is at the median nerve. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of the local anesthetic solution around the median nerve. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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The median nerve has no sensory branches in the forearm. Therefore, there is no advantage to blocking the median nerve at the elbow. Inserting the needle to elicit paresthesias can be quite painful for the patient. Blockade at the wrist is usually easier to perform, especially in obese patients.9
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Median Nerve Block at the Wrist
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The median nerve lies in the carpal tunnel on the volar aspect of the wrist. It is located between the tendons of the flexor carpi radialis and palmaris longus muscles (Figure 126-21C). The innervation of the median nerve is described in the previous section.
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Place the patient supine with their arm abducted 45°, the elbow in full extension, and the hand fully supinated (Figure 126-21A).
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Identify the palmaris longus tendon by flexing the patient's clenched hand against resistance. Mark the radial border of the palmaris longus tendon. Note the position of the proximal and distal wrist creases.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution along the radial border of the palmaris longus tendon, between the proximal and distal wrist creases. Insert a 25 gauge needle perpendicular to the skin wheal and advance it slowly (Figure 126-21C). If paresthesias are elicited, withdraw the needle 1 to 2 mm and allow them to resolve. Inject 3 to 5 mL of local anesthetic solution. If paresthesias are not elicited, inject 5 to 10 mL of local anesthetic solution. Injection of the local anesthetic solution should not raise a skin wheal and should flow effortlessly if the needle is within the carpal tunnel.12
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Place the US probe over the middle of the wrist with the marker pointing laterally (Figure 126-21D). The Palmaris longus tendon should be visible in the middle of the wrist. The median nerve is hyperechoic and directly lateral to this tendon (Figure 126-21E). The radial artery is lateral to the median nerve (Figure 126-21C). Anesthetize the skin lateral to the palmaris longus tendon. Place the needle inferior to the short axis of the US probe and directly over the median nerve (Figure 126-21D). Insert and advance the needle until its tip is at the median nerve. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of the local anesthetic solution around the median nerve. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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A small percentage of the population (10% to 15%) does not have a palmaris longus tendon. Identify the flexor carpi radialis tendon by the same method as identifying the palmaris longus tendon. Inject the local anesthetic solution 1 cm medial to the ulnar edge of the flexor carpi radialis tendon, between the proximal and distal wrist creases. The technique is otherwise as noted above.
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Ulnar Nerve Block at the Elbow
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The ulnar nerve lies in the ulnar groove of the humerus at the elbow, between the olecranon process and medial condyle of the humerus (Figure 126-22A). It provides motor innervation to the flexor carpi ulnaris, the ring and little finger portion of the flexor digitorum profundus, the palmaris brevis, the hypothenar muscles, the third and fourth lumbricals, the interossei, and the adductor pollicis muscles. It provides sensory innervation to the medial one-third to one-half of the palm, the palmar aspect of the ulnar half of the ring finger, and the entire little finger (Figure 126-20B). The ulnar nerve provides sensory innervation to the dorsomedial half of the hand, the little finger, and the ulnar half of the ring finger on the dorsal surface of the hand.24
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Place the patient supine with their elbow flexed 90° and the shoulder flexed 45° (Figure 126-22A).
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Identify the olecranon process and the medial epicondyle of the humerus by palpation. Palpate the groove between the olecranon process and the medial epicondyle. The ulnar nerve is located within this groove.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution 1 to 2 cm proximal to the ulnar groove. Insert a 25 gauge needle through the skin wheal and directed toward the ulnar groove. Aim the needle parallel to the ulnar groove and the course of the nerve (Figure 126-22A). Advance the needle into the ulnar groove and inject 5 to 7 mL of local anesthetic solution. If paresthesias are elicited, withdraw the needle 1 mm and allow them to resolve before injecting the local anesthetic solution.
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Place the US probe in the crease between the olecranon process and the medial epicondyle, with the marker pointing laterally. Two hyperlucent structures should be seen, the medial epicondyle medially and the olecranon process closer to the marker. The ulnar nerve is hyperechoic and courses between these two hyperlucent structures. Anesthetize the skin. Place the needle inferior to the short axis of the US probe and directly over the ulnar nerve. Only the tip of the needle will be visualized in this view. Insert and advance the needle until its tip is at the ulnar nerve. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of local anesthetic solution around the ulnar nerve. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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The ulnar nerve has no sensory branches in the forearm and thus may be blocked at the wrist or at the elbow. Blockade of the ulnar nerve at the elbow is not recommended. A fibrous sheath surrounds the ulnar nerve at the elbow requiring intraneural injection for a successful blockade. This can lead to residual neuritis and nerve dysfunction. Blocking the ulnar nerve several centimeters above the elbow may prevent these complications. Blockade at the wrist is very reliable and does not have the associated complications as at the elbow.
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Ulnar Nerve Block at the Wrist
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The ulnar nerve lies between the distal and proximal flexor skin creases of the wrist, lateral (or radial) to the flexor carpi ulnaris tendon and medial (or ulnar) to the ulnar artery (Figure 126-22B). The innervation of the ulnar nerve is described in the previous section.
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Place the patient supine with their arm abducted 45° to 90°, the elbow fully extended, and the hand supinated (Figure 126-22B).
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Identify the flexor carpi ulnaris tendon by flexing the patient's clenched hand against resistance. Mark the medial aspect of the flexor carpi ulnaris tendon. Identify the ulnar artery by its palpable pulsations between the proximal and distal wrist crease. Note the position of the proximal and distal wrist creases.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution in the quadrangle defined by the proximal flexor skin crease, the distal flexor skin crease, the lateral aspect of the flexor carpi ulnaris tendon, and medial to the ulnar artery. Insert a 25 gauge needle perpendicular to the skin wheal and slowly advance it 0.5 cm (Figure 126-22B). If paresthesias are elicited, withdraw the needle 2 mm and allow them to resolve. Inject 2 mL of local anesthetic solution once the paresthesias resolve. If paresthesias are not elicited, inject 3 to 5 mL of local anesthetic solution.
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Place the US probe over the middle of the wrist with the marker pointing laterally (Figure 126-22C). The Palmaris longus tendon should be visible in the middle of the wrist. Move the US probe medially until the ulnar artery is visible. The ulnar nerve is hyperechoic and directly medial to the ulnar artery (Figure 126-22D). Anesthetize the skin medial to the ulnar artery. Position the needle inferior to the short axis of the US probe and directly over the ulnar nerve (Figure 126-22C). Insert and advance the needle until its tip is at the ulnar nerve. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of local anesthetic solution around the ulnar nerve. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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This is the preferred approach to block the ulnar nerve. Blockade of the ulnar nerve at the wrist is very reliable and does not have the associated complications as at the elbow.25
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Radial Nerve Block at the Elbow
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The radial nerve and the sensory branch of the musculocutaneous nerve run together in the sulcus between the biceps and the brachioradialis muscle on the anterolateral aspect of the elbow. The radial nerve provides sensory innervation to portions of the dorsal arm and forearm, the dorsolateral half of the hand, and the dorsal proximal aspects of the thumb, index, middle, and radial half of the ring fingers (Figure 126-20).12 It provides motor innervation to the muscles on the posterior aspect of the arm, forearm, and hand.
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Place the patient supine with their elbow flexed 15° to 30°.
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Palpate the tendon of the biceps muscle in the antecubital fossa. Identify the flexion skin crease of the elbow. Palpation of the biceps tendon is greatly facilitated by having the patient flex their elbow 90° then contract and relax their biceps muscle. Identify the medial and lateral condyles of the humerus. Draw a line between the humeral condyles (Figure 126-23A). This line should be located at the level of the antecubital crease.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution 2 cm lateral to the biceps tendon and 1 cm proximal to the antecubital crease (Figure 126-23A). Insert a 25 gauge needle through the skin wheal and perpendicular to the skin (Figure 126-23A). Advance the needle 1 to 2 cm. Probe in a fan-like pattern until paresthesias are elicited. Withdraw the needle 1 to 2 mm and allow the paresthesias to resolve. Inject 5 to 7 mL of local anesthetic solution.
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Position the patient with their arm abducted 45°, the elbow in full extension, and the hand supinated. Place the US probe on the lateral aspect of the crease of the antecubital fossa. The radial nerve is lateral to the biceps tendon and the brachial artery (Figure 126-23A). Anesthetize the skin over the radial nerve. Place the needle inferior to the short axis of the US probe and directly over the radial nerve. Only the tip of the needle will be visualized in this view. Insert and advance the needle until its tip is at the radial nerve. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of local anesthetic solution around the radial nerve. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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Blockade of the radial nerve at the elbow is difficult, has limited applications, is painful for the patient, and often results in a large antecubital hematoma. The preferred technique is blockade at the wrist.
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Radial Nerve Block at the Wrist
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The radial nerve at the wrist consists of a trunk and terminal branches that arise in the forearm (Figure 126-23C). The innervation of the radial nerve is described in the previous section.
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Place the patient supine with their arm abducted 45°, the elbow fully extended, and the hand midway between supination and pronation (Figure 126-23C).
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Identify the radial artery by its pulsation at the level of the proximal wrist crease.
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Needle Insertion and Direction
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Place a skin wheal of local anesthetic solution 1 mm lateral to the radial pulse. Insert a 25 gauge needle 1 mm lateral to the radial pulse, through the skin wheal, and perpendicular to the skin (Figure 126-23C). Advance the needle 0.5 cm. If paresthesias are elicited, withdraw the needle 1 to 2 mm and allow them to resolve. Inject 2 mL of local anesthetic solution. If paresthesias are not elicited, inject 3 to 5 mL of local anesthetic solution. This will anesthetize the terminal trunk of the radial nerve. Infiltrate 5 to 7 mL of local anesthetic solution at the level of the extensor wrist crease, from the lateral aspect of the radius to the base of the fourth metacarpal (Figure 126-23C). This will anesthetize the terminal branches that arise in the forearm.
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Place the US probe over the middle of the wrist with the marker pointing laterally. The palmaris longus tendon should be visible in the middle of the wrist. Move the US probe laterally until the radial artery is visualized. The radial nerve is hyperechoic and directly lateral to the radial artery (Figures 126-23D). Anesthetize the skin lateral to the radial artery and directly over the radial nerve. Place the needle inferior to the short axis of the US probe and directly over the radial nerve. Insert and advance the needle until its tip is at the radial nerve. Aspirate to ensure that the needle tip is not in a blood vessel. Inject a test dose of 1 to 2 mL of local anesthetic solution. Watch the spread of local anesthetic solution around the radial nerve. If satisfactory, inject the remainder of the local anesthetic solution to produce the “donut sign.” If the test dose is not satisfactory, reposition the needle and inject another test dose.
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This is the preferred technique for blockade of the radial nerve.
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Perform the wrist block by blocking the radial, ulnar, and median nerves at the wrist. The technique for each specific nerve block was discussed previously. The wrist block provides complete anesthesia to the hand and is commonly used in hand surgery. It can be performed in the Emergency Department to provide anesthesia for burn management, foreign body removal, wound exploration, or extensive laceration repair. Wrist blockade is reliable but slow, as it requires extended time to block all three nerves at the wrist.12
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Intermetacarpal Nerve Block
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The principal nerves supplying the finger are the palmar digital nerves, which originate from the deep volar branches of the ulnar and median nerves in the region of the wrist. These nerves follow the artery along the lateral aspects of the bone and supply sensation to the volar skin, the interphalangeal joints, the distal finger, and the fingertip of all five digits.
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Two dorsal and two palmar nerves supply each finger. These nerves run along the phalanxes in the 2, 4, 8, and 10 o'clock positions.26 These nerves also supply the dorsal, distal aspect of the finger, including the fingertip and nail bed. The dorsal digital nerves originate from the radial and ulnar nerves that wrap around the dorsum of the hand. They supply the nail bed of the thumb and small finger and the dorsal aspect of all five digits up to the distal interphalangeal joints. The palmar and dorsal nerves need to be blocked in the case of the thumb and fifth finger.
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Place the patient sitting upright or supine with their hand pronated on a bedside examination table.
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Locate the web spaces and the metacarpal heads on each side of the finger to be blocked.
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Needle Insertion and Direction
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Insert a 25 gauge needle into the dorsal aspect of the web space on one side of the digit to be anesthetized (Figure 126-24A). Advance the needle approximately 0.5 cm. Inject 1 mL of local anesthetic solution. Repeat the procedure on the other side of the digit to be blocked. When blocking the second and fifth digits, a half-ring block is required on the ulnar aspect of the fifth digit and radial aspect of the second digit. When blocking the thumb, infiltrate the dorsum and sides in a half-ring manner.
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An alternative is the metacarpal head block. This technique can be used to anesthetize any of the fingers. Insert a 25 gauge needle perpendicular to the dorsum of the hand and adjacent to the metacarpal head on one side of the finger to be blocked (Figure 126-24B). Advance the needle 0.5 cm and inject 1 mL of local anesthetic solution. Repeat the procedure on the other side of the finger to be blocked. Some physicians prefer to perform this block on the volar aspect of the hand (Figure 126-24C). This technique is extremely painful and should be avoided.
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This block produces less swelling than does the ring block. Subsequently, there is less risk of vascular compromise. This is a less painful technique than the ring block.
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Digital Nerve Block (Ring Block) of the Finger
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The anatomy and innervation of the digital nerves are described in the previous section.
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Place the patient sitting upright or supine with their hand pronated on a bedside examination table.
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Locate the dorsum of the proximal phalanx to be anesthetized.
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Needle Insertion and Direction
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Insert a 25 gauge needle on the dorsal surface of the base of the proximal phalanx (Figure 126-24D(1)). Inject 1 mL of local anesthetic solution along the dorsal surface of the finger. Remove the needle and reinsert it downward, perpendicular to the phalanx and to a depth just past the base of the phalanx (Figure 126-24D(2)). Inject 1.0 to 1.5 mL of local anesthetic along the lateral aspect of the finger. Withdraw the needle, reinsert it on the other side of the finger to be blocked, and inject 1.0 to 1.5 mL of local anesthetic solution (Figure 126-24D(3)).
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An alternative is the half-ring block (Figure 126-24E). It is a variant of the ring block (Figure 126-24D). Inject 1.0 to 1.5 mL of local anesthetic solution on one side of the base of the proximal phalanx to be anesthetized. Repeat this procedure on the other side of the finger. The injection of local anesthetic on one side of the finger is termed the half-ring block. It takes two half-ring blocks to anesthetize a finger.
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The indications for a digital block include repair of finger lacerations and amputations, reductions of fractures and dislocations, incision and drainage of infections, removal of fingernails, and relief of pain from burns. Do not inject more than 5 mL of local anesthetic solution into a digit. Using local anesthetic agents that contain epinephrine is not recommended because the finger contains end arteries and may experience ischemia from the vasoconstrictive effects of epinephrine.