Chapter 36: Local and Regional Anesthesia

Before the availability of local anesthetics, local pain control for lacerations, fractures, and minor surgery was achieved by minimizing the pain response centrally, typically with opiates or alcohol. Procaine, which entered clinical use in 1904, was the only local anesthetic available for almost 40 years, but the short duration of action and high rate of allergic reactions limited its effectiveness. Lidocaine was introduced in 1943 and continues to be the local anesthetic most commonly used in the ED.^1,2 Additional local anesthetics are available for both topical and injectable use (Tables 36-1 and 36-2). Emergency physicians commonly use local and regional anesthetic techniques for potentially painful procedures performed in the ED.³ Regional anesthesia can also be used to control the pain of acute injuries and reduce the utilization of systemic analgesics.^4,5

PHARMACOLOGY

Local anesthetics are divided into two classes: esters and amides.^1,2 Both classes work by reversibly blocking sodium channels and inhibiting the propagation of nerve impulses.^1,2 Sodium channel blockade first affects the smaller nerve fibers, causing a reduction in pain and temperature sensation, followed by loss of touch, deep pressure sensation, and, finally, motor function. Esters are hydrolyzed by cholinesterase enzymes in plasma, whereas amides are metabolized by hepatic microsomal enzymes. Onset of action, duration of anesthesia, and potential for systemic toxicity are the three primary factors in selecting a local anesthetic.

The onset of action of a local anesthetic is dependent on the pK_a (the pH at which 50% of the drug is ionized and 50% of the drug is nonionized). If the ambient pH is higher than the pK_a of the agent, a greater percentage of the drug will be in the nonionized form, which diffuses more rapidly across lipid membranes, and the onset of action is shorter. Thus, drugs with a lower pK_a have a more rapid onset of action. The pH of available local anesthetic solutions is acidic, varying from 3.3 to 6.8, depending on the agent, additives, and buffers. The duration of action of the local anesthetics is a function of receptor affinity. Agents with a higher receptor affinity (e.g., bupivacaine, ropivacaine, levobupivacaine) have a longer duration of action than those with lower receptor affinity (e.g., lidocaine, prilocaine).⁶ Selecting agents with a longer duration of action provides superior results for long procedures or for those in which postprocedure analgesia is desired. Longer-acting agents also offer continued analgesia when providers are pulled away from the procedure. The downside of long-acting agents is the greater risk of systemic toxicity.⁷ Levobupivacaine⁸ and ropivacaine⁹ appear to have a lower risk of systemic toxicity than bupivacaine.

Systemic Toxicity of Local Anesthetics

The systemic toxicity of local anesthetics occurs with dose-related clinical progression of sodium channel blockade in nontarget tissues, primarily the brain and heart.^10,11 Toxicity can range from subtle neurologic symptoms to refractory seizures and, ultimately, cardiovascular collapse (Figure 36-1).^12,13,14 The risk of systemic toxicity can be reduced by adherence to dose limitation and techniques to minimize systemic absorption.^15,16,17,18 Seizures due to neurologic toxicity should be treated with benzodiazepines.¹⁹ Typical agents used to treat cardiac arrest (e.g., vasopressin) and tachyarrhythmias (e.g., β-blockers and calcium channel antagonists) should be avoided in the setting of local anesthetic systemic toxicity.¹⁹ IV 20% lipid emulsion is an effective treatment for systemic toxicity from local anesthetics, especially if due to bupivacaine with its high lipid solubility.^{19, 20, 21, 22, 23, 24, 25, 26, 27} Published reports have utilized different dosing protocols, but one consensus guideline recommends an initial dose of 20% lipid emulsion, 1.5 mL/kg infused over 1 minute with continuous infusion or repeat doses according to the clinical condition.¹⁹ The recommended maximum dose is about 10 mL/kg over the initial 30 minutes.¹⁹

Prilocaine and benzocaine can cause the oxidation of the ferric form of hemoglobin to the ferrous form, creating methemoglobin that becomes visible as cyanosis when methemoglobin concentration exceeds 1.5 grams/dL.

GENERAL PRINCIPLES OF LOCAL ANESTHETIC USE

When using any local anesthetic, calculate the volume and concentration of drug used, especially when treating smaller patients or tending to large wounds (Table 36-2). Aspiration before injection helps to avoid inadvertent deposit of local anesthetic in a vein or artery. When the use of a large quantity of local anesthetic seems unavoidable, procedural sedation or alternative regional blocking techniques and supplementation with systemic analgesics or anxiolytics should be considered (see chapter 37, Procedural Sedation).

The addition of epinephrine to the injected local anesthetic solution increases the duration of anesthesia, helps to control wound bleeding, and slows the systemic absorption.²⁸ The use of local anesthetic with epinephrine is safe for use in end-arterial fields (fingers, toes, etc.) in selected healthy patients,^{29, 30, 31, 32, 33, 34} but probably should be avoided in suspected digital vascular injury; patients with vascular disease, such as Raynaud's or Berger's disease; or other conditions in which end-arterial vascular supply is problematic. An alternative to epinephrine is clonidine (U.S. Food and Drug Administration unlabeled use), an α-adrenergic agonist, which can also be used in combination with a local anesthetic to prolong the duration of anesthesia.^35,36,37 A dose of 0.5 micrograms/kg of clonidine (maximal dose 150 micrograms) can be mixed with the anesthetic to prolong the duration of anesthesia by >50%. Do not exceed a maximal dose of 150 micrograms because sedation, hypotension, and bradycardia can result.^36,37

Adverse reactions to local anesthetics are most often local reactions to preservatives or the epinephrine in the solution, and true allergic reactions are extremely rare.^38,39 In patients with true allergies to local anesthetics, two nontraditional agents can be used for wound repair via local injection—diphenhydramine and benzyl alcohol (Table 36-2).^40,41,42

The addition of sodium bicarbonate to local anesthetics shortens the onset of action by raising tissue pH and reduces the pain of injection.^3,43,44,45 Lidocaine can be buffered by adding 1 mL of sodium bicarbonate 8.4% (1 mEq/mL) to 9 mL of 1% lidocaine. Bupivacaine can be buffered by adding 1 mL of sodium bicarbonate 8.4% (1 mEq/mL) to 29 mL of bupivacaine 0.25%. However, the addition of bicarbonate can cause precipitation of the anesthetic agent (most prominently bupivacaine) and accelerate the degradation of epinephrine in the solution, so bicarbonate should not be added to the anesthetic unless it can be used immediately. Additional means of reducing the pain of infiltration include the use of a 27- to 30-gauge needle, slow injection, warming the solution to body temperature, and injecting through the margins of a wound rather than through intact skin surrounding the wound.^{3,43, 44, 45, 46, 47, 48}

Local anesthetics can be administered topically, intradermally, subdermally, or infiltrated near peripheral nerves. When considering which approach best meets the patient's needs, many factors should be considered. In the setting of wound management, these include patient factors (age, anticipated pain tolerance, comorbidities), wound factors (location, depth, presence or absence of contamination, and/or neurovascular injury), and technical factors (time required, clinician experience). Clinical judgment combined with individual patient needs should dictate the best approach.

Topical anesthetics are used in three major situations: on intact skin before dermal instrumentation, applied to intact mucosa, and placed on open skin for pain control or before wound repair.^49,50,51 Topical anesthetics are probably as effective as local anesthetic infiltration for suturing of many dermal lacerations, although the comparison studies are of modest quality.⁵²

An alkaline (pH approximately 9) cream mixture of lidocaine and prilocaine [eutectic mixture of local anesthetics (EMLA^®)] was the first topical anesthetic formulated to penetrate intact skin. When applied for at least 60 minutes under a semiocclusive dressing before dermal instrumentation, this lidocaine/prilocaine mixture is as efficacious as the infiltration of local anesthetic and is ideal for venous catheter insertion and lumbar puncture. Liposome-encapsulated tetracaine, liposome-encapsulated lidocaine, and tetracaine gel have all been compared to the lidocaine/prilocaine mixture and found to be equally efficacious (Table 36-1).^{53,54,55,56,57}

The tetracaine, epinephrine, and cocaine mixture is a topical anesthetic used on open dermis. Due to the potential for CNS and cardiovascular toxicity, the cocaine component of this combination has been replaced with lidocaine. This mixture—lidocaine, epinephrine, and tetracaine—has a variety of formulations and is usually compounded by the hospital pharmacy in accordance with the concentration preferences of local clinicians. A common version is 4% lidocaine, 0.1% epinephrine, and 0.5% tetracaine prepared in 5-mL vials.

Intradermal injection produces a visible wheal, whereas subdermal injection does not. Intradermal injection produces more immediate pain upon injection due to stretching of the compact dermal structure, but can enhance the anesthetic effect by applying pressure to and numbing the cutaneous pain sensors. Intradermal injection raises the skin surface and is useful when shaving off a cutaneous lesion. Subdermal injections have a slower onset of action, are less painful, and are the most commonly used method of achieving local anesthesia in the ED and for office-based surgery.^3,58 Local anesthetics may be delivered directly into the subdermal space in most clean lacerations or as a field block for contaminated wounds.

In addition to modifying the injected solution, a variety of techniques are used to reduce the pain of needle puncture and local anesthetic injection^43,44,45,59: application of a topical anesthetic prior to injection,^60,61 warming the local anesthetic agent,^46,47,48 stretching the skin at the puncture site, vibrating the skin adjacent to the area,^62,63 talking during the process to distract the patient, inserting the needle through enlarged pores or hair follicles, inserting the needle with bevel up position,⁶⁴ or numbing the skin with an aerosol refrigerant.^{65,66,67,68,69}

Regional anesthesia is a technique that infiltrates local anesthetic agents adjacent to peripheral nerves ("nerve blocks") and is typically used for complicated lacerations, abscesses, fractures, and dislocations.^70,71,72 Providing adequate anesthesia quells patient anxiety, provides greater patient satisfaction, and increases the likelihood of an optimal result when treating complex injuries. With careful technique, serious complications from peripheral nerve blocks are uncommon.^73,74,75 Assess and document distal neurovascular status before application of a regional nerve block to prevent masking a primary traumatic neurovascular injury. Distal vascular function is assessed by noting skin color and temperature, measuring capillary refill time, and palpating pulses. Distal neurologic function is assessed by noting cutaneous sensation (pain, touch) and motor function (active movement, strength). For digital injuries, assess digital nerves by determining two-point discrimination on the volar pad before anesthetic injection. Normal two-point discrimination is <6 mm at the fingertips and is often <2 mm. Compare the injured digit with the contralateral normal digit.

Regional anesthesia for laceration repair eliminates wound distortion caused by large-volume subdermal injection. Regional anesthesia on the extremities provides superior pain control when compared with subdermal infiltration of anesthetic.⁷⁰ Topical anesthetic before peripheral nerve blocks can minimize the pain associated with the block.^{53,54,55,56,57,60,61}

When selecting a local anesthetic for regional anesthesia, consider the onset of clinical effects, duration of analgesia, and risk of toxicity.⁷⁰ Although lidocaine continues to be the most popular agent, bupivacaine, levobupivacaine, and ropivacaine offer a longer duration of action, with levobupivacaine and ropivacaine being significantly less cardiotoxic.^6,8,9 Peripheral nerve blocks require time to achieve optimal analgesia, approximately 10 to 20 minutes for lidocaine and 15 to 30 minutes for bupivacaine. Pain and temperature sensation are affected first, followed by loss of touch, deep pressure, and then motor function. Intraneural injection of anesthetic causes significant pain.⁷⁶ Thus, if excessive pain upon injection is noted, withdraw the needle a few millimeters, and after pain abates, resume the injection.

The regional nerve blocks commonly performed by emergency physicians are often done using the "landmark" technique to identify the site of local anesthetic injection.⁷⁰ The major disadvantage of the landmark approach is anatomic variation. Large volumes of anesthetic are typically administered, in case the needle tip is not close to the desired nerve. Two devices in common use help localize and direct the needle to maximize the rate of successful anesthesia: a peripheral nerve stimulator using electrically insulated needles and US guidance to localize the nerve.^{77,78,79,80,81} US guidance shortens the block performance time, reduces the number of needle passes, and enables blocks to be performed using lower anesthetic doses.^82,83,84 Training to use US-guided regional anesthesia in the ED typically involves a didactic session, supervised practice in ultrasonographic identification of the relevant structures, and procedural practice on simulation mannequin.^85,86 The use of US is recommended when performing more complex nerve blocks.

The performance of peripheral nerve blocks requires an element of hand–eye coordination that is difficult to display in words and photographs.

DIGITAL BLOCKS

Digital Nerve Block

Purpose A digital nerve block provides anesthesia to the entire digit and is an excellent block when tending to lacerations of the fingers or toes, drainage of paronychia, finger or toenail removal or repair, and reduction of fractured or dislocated fingers or toes.⁸⁷ Use of topical anesthesia before instrumentation can quell anxiety about the procedure and minimize pain. Assess distal capillary refill and two-point discrimination (normal <6 mm) on the volar pad before application of the block. For digital blocks, there is less pain with injection using lidocaine 1% with epinephrine compared to bupivacaine 0.5%, but the duration of anesthesia is only about half as long.⁸⁸

Patient Positioning and Anatomy The hand and wrist are placed in a prone (palm down) position. The common digital nerves are derived from the median and ulnar nerves. In the distal palm, the common digital nerve divides into paired palmar branches that travel on both sides of the flexor tendon sheath and innervate the lateral and palmar aspect of each digit. The dorsal digital nerves are smaller, derived from the radial and ulnar nerves, and travel on the dorsal lateral aspect of each finger to provide sensation to the back of the finger.

Technique Insert the needle on the dorsal surface of the proximal phalanx, advance toward the volar surface staying tangential to the phalanx, aspirate to ensure no inadvertent vascular puncture has occurred, deposit 1 mL of anesthetic solution, and inject an additional 1 mL while withdrawing the needle back to the skin surface (Figure 36-2). Reinsert the needle in the same location, but direct it across the dorsum of the digit to the other side, and inject a 1-mL band of anesthetic solution into the subcutaneous space across the dorsum of the digit. Repeat the initial injection process on the other side of the digit.

Transthecal or Flexor Tendon Sheath Digital Nerve Block

Purpose A transthecal or flexor tendon sheath digital nerve block provides anesthesia to the entire digit by utilizing the flexor tendon sheath to apply anesthetic to the digital nerves.⁸⁹ This procedure can be performed in addition or as an alternative to a digital nerve block. However, flexor tendon sheath block may not fully anesthetize the distal fingertip.

Patient Positioning and Anatomy The hand and wrist are placed in a supine (palm up) position. The flexor tendon sheath surrounds the flexor tendon on the palmar side of the digit.

Technique Identify the distal palmar crease on the palmar aspect of the hand. Have the patient flex the finger against resistance to improve visualization of the flexor tendon. Identify the distal palmar crease of the digit to be blocked, and insert the needle at a 45-degree angle to the palmar plane with the tip pointed distally (Figure 36-3). Advance the needle until a "pop" is felt, indicating penetration of the flexor tendon sheath. Inject 2 to 3 mL of anesthetic solution. If bone is struck before the "pop" is felt, withdraw the needle 2 to 3 mm and inject the solution.

A modification of the transthecal approach is to inject into the flexor tendon sheath at the base of the digit in the metacarpal crease^90,91 or into the midportion of the proximal phalanx.⁹²

HAND AND WRIST BLOCKS

The median, radial, and ulnar nerves supply the sensory innervation to the hand and can be used in part or in combination to provide anesthesia for lacerations, puncture wounds, or fracture/dislocation reductions (Figures 36-4 and 36-5).

Median Nerve Block

Purpose A median nerve block provides anesthesia to the thumb, index, long, and half of the ring finger distal to the proximal interphalangeal joint, but not the dorsum of the thumb (Figures 36-4 and 36-5).

Patient Positioning and Anatomy The hand and wrist are placed in a supine (palm up) position. The median nerve traverses between the flexor carpi radialis and the palmaris longus tendon at the proximal wrist crease. With the hand and wrist in a supine position, the flexor carpi radialis is lateral (radial direction) and the palmaris longus is medial (ulnar direction) to the nerve. When the patient makes a fist and flexes the wrist, the palmaris longus tendon is usually the more prominent of the two tendons (Figure 36-6, top left).

Technique Raise a wheal of anesthetic in the subcutaneous space between the palmaris longus and flexor carpi radialis at the level of the proximal palmar crease (Figure 36-6, right). Insert the needle until the "pop" of the deep fascia can be felt, and inject 3 to 5 mL of anesthetic. If bone is contacted before the "pop" is felt, withdraw the needle 2 to 3 mm and inject the solution. To increase the probability of a successful block, withdraw the needle back to the skin and reinsert, directing the needle 30 degrees medially and laterally, and inject an additional 1 to 2 mL of anesthetic solution. The palmar branch of the medial nerve is superficial and can be blocked by withdrawing the needle to the subcutaneous space and injecting 2 to 3 mL of anesthetic solution.

Radial Nerve Block

Purpose A radial nerve block provides anesthesia to the dorsal lateral half of the hand and dorsal aspect of the thumb.

Patient Positioning and Anatomy The hand and wrist start in a neutral position (thumb side up) and then rotate into a prone (palm down) position. The superficial branch of the radial nerve traverses above the styloid process of the radius and provides sensation to the dorsum of the thumb, index finger, and lateral half of the middle finger (Figures 36-4 and 36-5). Other branches of the radial nerve traverse over the anatomic snuff box. The anatomic snuff box is formed by the extensor tendons of the pollicis brevis and longus and the radial styloid.

Technique Raise a wheal of anesthetic in the subcutaneous space just proximal to the anatomic snuffbox. Inject 5 mL of anesthetic solution into the subcutaneous tissue overlying the radial styloid (Figure 36-6, right). Then, reinsert the needle and direct it through the subcutaneous space in a lateral (ulnar) direction, injecting a band of an additional 5 mL of anesthetic solution to ensure blockage of the smaller branches of the radial nerve (Figure 36-6, lower left). The distribution of the radial nerve is less predictable; therefore, a generous amount of anesthesia should be injected.

Ulnar Nerve Block

Purpose An ulnar nerve block provides anesthesia to the entire fifth digit, half of the fourth digit, and the medial aspect of the hand and wrist.

Patient Positioning and Anatomy The hand and wrist are placed in a supine (palm up) position. The ulnar nerve travels with the corresponding vein and nerve and can be located underneath (deep) to the flexor carpi ulnaris. To identify the flexor carpi ulnaris, have the patient make a fist and tense the wrist. The flexor carpi ulnaris is the most prominent tendon on the ulnar side at the wrist (Figure 36-7A).

Technique Raise a wheal of anesthetic in the subcutaneous space just proximal (1 to 2 cm) to the most distal wrist crease. Insert the needle under the flexor carpi ulnaris tendon to an additional 5 to 10 mm past the edge of the tendon (Figure 36-7C). Aspirate before injection to ensure that inadvertent arterial/venous puncture has not occurred, and inject 3 to 5 mL of anesthetic solution. To block the dorsal branches of the ulnar nerve, inject 2 to 3 mL of anesthetic solution in the subcutaneous space just above the tendon of the extensor carpi ulnaris (Figure 36-7B). US guidance can be useful when anatomic landmarks are not easy to discern.⁹³

FOOT AND ANKLE BLOCKS

The five nerves that provide sensation to the foot are four branches of the sciatic nerve (deep and superficial peroneal, tibial, and sural nerves) and one cutaneous branch of the femoral nerve (saphenous nerve; Figures 36-8, 36-9, 36-10 and 36-11). These are excellent blocks to use alone or in combination for lacerations, fracture reductions, and exploring wounds. The deep peroneal nerve and the posterior tibial nerves are deep nerves and can be more consistently found by anatomic landmarks. The superficial peroneal, sural, and saphenous nerves are superficial and located in the subcutaneous tissue encircling the ankle. Due to the anatomic variability of these three nerves, no single injection point can reliably provide adequate anesthesia, so these nerves are blocked by depositing the local anesthetic agent as a field block in the subcutaneous space in the area through which the nerve travels. The pertinent landmarks for performing all of the ankle blocks are the extensor hallucis longus, tibialis anterior tendon, Achilles tendon, and the medial and lateral malleolus (Figure 36-12).

When all five blocks are used for complete foot anesthesia, the deep nerves (deep peroneal and posterior tibial) should be anesthetized before the surface anatomy is distorted by the superficial field blocks of the other three. An additional tip is to prepare and clean the entire foot before starting so that the physician can change his or her body position and reposition the patient's foot as needed to avoid awkward reaches when accessing all five sites.

Deep Peroneal Nerve Block

Purpose A deep peroneal nerve block provides anesthesia to the web space between the first and second toe and a small area just proximal to the first and second toe on the plantar aspect of the foot.

Patient Positioning and Anatomy The foot is placed in a neutral position. At the level of the medial malleolus, the deep peroneal nerve can be found between the extensor hallucis longus and the tibialis anterior tendon. Extension of the big toe against resistance will help to identify the extensor hallucis longus. Dorsiflexion and inversion of the ankle will help to identify the tibialis anterior tendon.

Technique Raise a wheal of anesthesia in the subcutaneous space between the extensor hallucis longus and the tibialis anterior tendon at the level of the medial malleolus (Figure 36-12B). With the syringe perpendicular to the skin, insert the needle until the extensor retinaculum is penetrated or bone is struck. If bone is struck, withdraw the needle 2 mm. After aspirating to verify that no vascular structure has been entered, inject approximately 2 to 3 mL of anesthetic solution. To increase the chance of a successful block, withdraw the needle back to the skin and reinsert, direct the needle 30 degrees medially and laterally, and deposit an additional 2 mL of anesthetic solution on each side.

Posterior Tibial Nerve Block

Purpose A posterior tibial nerve block provides anesthesia to the plantar aspect of the foot. This is an excellent block when repairing a laceration on the bottom of the foot.

Patient Positioning and Anatomy The patient can be either supine with the foot rotated outward or prone with the foot rotated inward. The posterior tibial nerve, artery, and vein can be found just posterior to the medial malleolus. The nerve is deep to the fascia and superficial/posterior to the artery.

Technique Raise a wheal of anesthesia posterior to the medial malleolus. Palpate the posterior tibial artery and insert the needle just posterior to the artery until it is deep to the fascia or bone is struck (Figure 36-12A and C). If bone is struck, withdraw the needle 2 mm. Inject 2 to 3 mL of local anesthetic solution after aspirating to ensure that inadvertent arterial/venous puncture has not occurred. To increase the chance of a successful block, withdraw the needle back to the skin and reinsert, directing the needle 30 degrees medially and laterally, and deposit an additional 2 mL of anesthetic solution on each side. US guidance can be used to guide the needle and increase the completeness of a posterior tibial nerve block.⁹⁴

Superficial Peroneal Nerve Block

Purpose A superficial peroneal nerve block provides anesthesia to the dorsal lateral aspect of the foot.

Patient Positioning and Anatomy The patient is supine, and the foot is rotated inward. The superficial peroneal nerve traverses the lateral portion of the ankle in the subcutaneous space between the lateral malleolus and the tibialis anterior tendon.

Technique Prepare a sterile site between the superior border of the lateral malleolus and the tibialis anterior tendon. Dorsiflexion and inversion of the ankle will help to identify the tibialis anterior tendon. In the subcutaneous space, inject 5 mL of anesthetic, tracking from the tibialis anterior tendon to the superior portion of the lateral malleolus (Figure 36-12B). Creation of a subcutaneous wheal indicates proper anesthetic placement.

Sural Nerve Block

Purpose A sural nerve block provides anesthesia to the lateral aspect of the ankle with some extension of anesthesia to the plantar aspect of the foot.

Patient Positioning and Anatomy The patient can be either supine with the foot rotated inward or prone with the foot rotated outward. The sural nerve traverses the posterior lateral portion of the ankle in the subcutaneous space between the Achilles tendon and the lateral malleolus.

Technique Identify the space between the Achilles tendon and the superior border of the lateral malleolus. In the subcutaneous space, inject 5 to 6 mL of anesthetic solution in a band running from the superior portion of the lateral malleolus to the Achilles tendon (Figure 36-12A). Creation of a subcutaneous wheal indicates proper anesthetic placement. US guidance by injecting the local anesthetic around the lesser saphenous vein may facilitate a more complete and longer duration block.⁹⁵

Saphenous Nerve Block

Purpose A saphenous nerve block provides anesthesia to the medial aspect of the ankle.

Patient Positioning and Anatomy The foot is in a neutral position. The saphenous nerve traverses the anterior medial portion of the ankle in the subcutaneous space between the tibialis anterior tendon and the medial malleolus.

Technique Identify the space between the tibialis anterior tendon and the superior border of the medial malleolus. In the subcutaneous space, inject 5 to 6 mL of anesthetic solution from the tibialis anterior tendon to the superior portion of the medial malleolus (Figure 36-12C). Creation of a subcutaneous wheal indicates proper anesthetic placement.

FACIAL NERVE BLOCKS

Facial nerve blocks provide excellent analgesia and little to no distortion of the forehead, cheek, and chin (Figure 36-13).^70,96 Topical anesthetic applied to the mucosa should be used before the intraoral approach for infraorbital and mental nerve blocks. It is important to assess neurovascular status before application of the block to prevent masking a primary traumatic neurovascular injury.

Supraorbital and Supratrochlear Nerve Blocks

Purpose Supraorbital and supratrochlear nerve blocks provide anesthesia to the entire forehead up to the vertex of the scalp and down the bridge of the nose.

Patient Positioning and Anatomy The patient is either supine or sitting. The supraorbital nerve exits the supraorbital foramen, which is in line with the pupil and above the superior orbital rim. The supratrochlear nerve exits from under the superior orbital rim 5 to 10 mm medial to the supraorbital foramen. The supraorbital nerve supplies most of the forehead, whereas the supratrochlear nerve supplies the area along the bridge of the nose (Figure 36-13).

Technique Raise a wheal of anesthesia in the subcutaneous space just superior to the eyebrow and in line with the pupil. Deposit 2 to 3 mL of anesthetic solution in the subcutaneous space, and then direct the needle medially to raise a horizontal wheal reaching to the medial border of the eyebrow using an additional 5 mL of anesthetic solution (Figure 36-14).

Infraorbital Nerve Block

Purpose An infraorbital nerve block provides anesthesia to the lower lid, medial cheek, ipsilateral side of the nose, and the ipsilateral upper lip (Figure 36-13).

Patient Positioning and Anatomy The patient is either supine or sitting. The infraorbital nerve exits the infraorbital foramen 5 to 10 mm inferior to the midportion of the orbital rim and just cranial (superior) to the maxillary canine teeth (tooth #6 on the patient's right and #11 on the patient's left).

Technique After adequately providing topical anesthetic to the mucosa superior to the maxillary canine, dry the mucosa and retract the upper lip. The recommended technique involves placing the index finger and middle finger of the noninjecting hand on the inferior optic rim and everting the upper lip with the thumb. Insert the needle at the gingival reflection above the maxillary canine, direct the needle superiorly, advance approximately half the distance from the entry site to the orbital rim, and inject 3 to 5 mL of anesthetic solution (Figure 36-14). Depending on the patient's anatomy, it may be possible for the physician's index or middle finger to palpate the infraorbital foramen through the skin and direct the needle to this site.

Mental Nerve Block

Purpose A mental nerve block provides anesthesia to the labial mucosa, gingiva, and lower lip adjacent to the incisors and canines.

Patient Positioning and Anatomy The patient can be either supine or sitting. The inferior alveolar nerve gives rise to the mental nerve, which exits the mental foramen, located inferior to the mandibular canines and first premolars (teeth #21 and #22 on the patient's left, and #27 and #28 on the patient's right).

Technique After adequately providing topical anesthetic to the mucosa inferior to the canine and first premolars, dry the mucosa and evert the lower lip. Insert the needle at the gingival reflection at this site, direct the needle inferiorly, advance approximately 1 cm, and inject 3 to 5 mL of anesthetic solution (Figure 36-15). Depending on the patient's anatomy, it may be possible for the physician's finger to palpate the mental foramen through the skin and direct the needle to this site.

Auricular Block

Purpose An auricular block provides anesthesia to the entire ear.

Patient Positioning and Anatomy Patient can either be supine or sitting. The sensation to the ear is provided anteriorly by the auriculotemporal nerve and posteriorly by the greater auricular nerve and the mastoid branch of the lesser occipital nerve.

Technique Raise a wheal in the subcutaneous space inferior to the auricle. From this site, direct the needle in the subcutaneous space anterior and superior, and inject 2 to 3 mL of anesthetic while withdrawing the needle (Figure 36-16). From the original injection point, redirect the needle posteriorly and superiorly and deposit 2 to 3 mL in the subcutaneous space while withdrawing the needle. Repeat this process from the superior aspect of the ear, injecting 2 to 3 mL of local anesthetic in the subcutaneous space both anterior and posterior to the ear to complete the field block around the ear.

INTERCOSTAL NERVE BLOCK

Purpose

An intercostal nerve block provides analgesia to the intercostal nerve above and below the affected rib in a band-like fashion around the chest wall. These blocks provide an alternative to parenteral analgesia for controlling pain from rib fractures that make movement and normal respiration quite painful^97,98 and for placement of tube thoracostomy.⁹⁹ Although controlled trials comparing parenteral analgesia with intercostal nerve blocks are lacking, clinical observations suggest better pain control and increased lung function associated with intercostal blocks.¹⁰⁰ A good intercostal block will provide anesthesia duration between 8 and 18 hours.

Patient Positioning and Anatomy

Patient is sitting upright, with the ipsilateral arm raised at the shoulder and the wrist rested on top of the head. Within the subcostal groove of the rib, the intercostal nerve originates from the thoracic nerve and runs inferior to the artery and vein ("vein, artery, nerve"). Ribs 1 through 6 are difficult to block due to the position of the scapula and rhomboid muscles. With both anterior and posterior rib fractures, the optimal block site is at the "rib angle," approximately 6 cm lateral to the midline, or just lateral to the paraspinous muscles. Blocking posterior to the midaxillary line ensures analgesia to the lateral cutaneous and anterior branch of the intercostal nerve (Figure 36-17, right).

Technique

Palpate the inferior border of the rib to be blocked with the noninjecting hand, and retract the skin cephalad at a location about 6 cm from the midline. Raise a wheal in the subcutaneous space, and insert the needle bevel up with the syringe lower than the entry site. The optimal angle is approximately 10 to 15 degrees off the perpendicular with the needle tip angled cephalad (Figure 36-17, top). Continue inserting the needle until it contacts bone. The needle should be resting at the inferior border of the rib to be blocked. Release the skin being retracted with the noninjecting hand, walk the needle caudally until it drops off the inferior edge of the rib, and advance the needle approximately 3 mm. This is the subcostal groove. Aspirate before injection, and deposit 2 to 5 mL of anesthetic.

The patient should be monitored for 30 minutes after the procedure to watch for clinical signs of pneumothorax. A postprocedure chest x-ray is not routinely indicated unless clinical signs of pneumothorax, including coughing, shortness of breath, or hypoxia, occur. Pneumothorax occurs in 8% to 9% of patients, or at a rate of about 1.4% for each individual intercostal block.¹⁰¹

FEMORAL NERVE BLOCK

Purpose

Regional anesthesia in the femoral region can result in an isolated femoral nerve block or a larger block involving the femoral, obturator, and lateral femoral cutaneous nerves. These blocks provide good to excellent pain control for patients with proximal femur and hip fractures and are especially useful in the elderly.^{102,103,104,105} The "three-in-one" block uses the same injection location as a femoral nerve block but applies distal pressure to promote cephalad distribution of the anesthetic agent to block the obturator and lateral femoral cutaneous nerves.¹⁰⁶ It is important to assess distal neurovascular status before application of the block to prevent masking a primary traumatic neurovascular injury.

Patient Positioning and Anatomy

The patient is in a supine position. In obese patients, placement of a pillow underneath the hip and retraction of the lower abdominal pannus superiorly and laterally will help expose the area. At the inguinal ligament and the inguinal (femoral) crease, the femoral nerve is positioned lateral to and slightly deeper than the femoral artery (Figure 36-18). The femoral nerve block will provide anesthesia to the anterior thigh and medial leg. The "three-in-one" block anesthetizes regions innervated by the obturator and the lateral femoral cutaneous nerves in addition to the anterior thigh and medial leg.

Technique

A peripheral nerve stimulator or US guidance is recommended.^{77, 78, 79, 80, 81, 82, 83, 84,107,108} Ropivacaine is an excellent long-acting anesthetic with a relatively lower cardiac toxicity.^6,8,9

Locate the femoral artery on the affected side at the level of the inguinal crease. Palpate the femoral artery with the noninjecting hand, and raise a wheal of anesthetic in the subcutaneous space at the level of the inguinal crease and 1 cm lateral to the femoral artery. Insert the needle at this site and directed slightly cephalad (Figure 36-18). The femoral nerve is a relatively superficial nerve, typically 2 to 3 cm below the skin.

If a peripheral nerve stimulator is being used, needle position is confirmed by contraction of the quadriceps muscle and subsequent patellar movement. If the sartorius muscle contracts, the needle should be repositioned slightly lateral and deeper. The sartorius muscle may mimic the quadriceps contractions, but the patella will only move with quadriceps contractions. US guidance can also be used to accurately place the anesthetic agent for a femoral nerve block.¹⁰⁸

If a peripheral nerve stimulator is not being used, correct positioning of the needle is confirmed by the patient reporting paresthesia over the anterior thigh as the needle impacts the femoral nerve. Back the needle off slightly and inject approximately 20 mL of the anesthetic solution into the perineural space. If paresthesia over the anterior thigh cannot be elicited, the needle should be withdrawn to the skin, redirected 10 to 15 degrees laterally, and advanced as before. More lateral skin insertions may be required to locate the femoral nerve. Alternatively, a "blind" attempt can be made by injecting a larger quantity (30 to 40 mL) of anesthetic solution in and around the original site in an effort to spread the anesthetic through the region and reach the femoral nerve. Aspirate before each injection to avoid inadvertent arterial puncture, and do not inject if resistance is felt, as this indicates the possibility for intraneural injection.

To perform a "three-in-one" block, needle position should be confirmed by paresthesia or preferably by US.¹⁰⁷ Firm pressure distal to the injection site is then applied and held for 5 minutes as 20 to 30 mL of anesthetic solution is delivered. This distal pressure promotes cephalad distribution of the anesthetic solution.

An alternative to the femoral nerve block for pain control in patients with hip and femoral neck fractures is the fascia iliaca compartment block that has been recently studied in ED patients.^109,110

PURPOSE

Hematoma blocks are commonly performed for fracture reduction, utilizing the hematoma formation around the fracture to deliver anesthetic to the fracture site, most commonly for Colles' fractures.^111,112,113 This block has waned in use due to the rising popularity of procedural sedation and the misconception that hematoma blocks dramatically increase the risk of infection. The hematoma block remains a staple in the armamentarium of fracture analgesia, because it is simple, fast, and requires no special tools or personnel.

PATIENT POSITIONING

The patient is usually supine with the limb placed to access the fracture hematoma.

TECHNIQUE

Prepare a sterile block site over the bony fracture site and insert the needle directly into the hematoma (Figure 36-19). Positioning the needle in the hematoma can be difficult at times. Aspiration of blood aids in confirmation of needle position. Inject 5 to 15 mL of local anesthetic solution into the fracture site. When performing this block, ensure that the maximum dose of local anesthetic is not exceeded. This procedure should not be performed through a contaminated wound or an open fracture.

PURPOSE

The Bier block provides dense anesthesia in a limb for up to 60 minutes without the risks of general anesthesia. It is an excellent block for large complex lacerations, fracture reductions, and surgical procedures of <1 hour duration on the extremities¹¹⁴ and does not require fasting for safe performance.¹¹⁵ Although this block is relatively easy to perform, it does require a specialized pneumatic tourniquet and provides no postprocedure pain control. Because the local anesthetic solution is directly infused into the venous system, careful attention to technique is important to prevent systemic toxicity.¹¹⁶ It is important to assess neurovascular status in the involved limb before application of the block to prevent masking a primary traumatic neurovascular injury.

TECHNIQUE

Place two IV catheters, one small gauge in the affected extremity and the other in the unaffected extremity for fluid administration and sedation, if needed. Apply the specialized double-cuff pneumatic tourniquet to the affected upper arm or thigh. The standard blood pressure cuff is not an acceptable alternative. Provide adequate padding beneath the cuff, as this is often the site of maximal discomfort during the procedure.

Exsanguinate the affected extremity by either elevating it for 3 to 4 minutes or wrapping the extremity with a compression bandage from distal to proximal. The cuffs are then inflated in the following sequence: Inflate the distal cuff first, followed by inflating the proximal cuff and, finally, deflating the distal cuff. In the upper extremity, inflate the pneumatic tourniquet to 250 to 300 mm Hg (30 to 45 kPa) or 100 mm Hg (15 kPa) above the patient's systolic blood pressure. In the leg, cuff inflation pressures are 350 to 400 mm Hg (45 to 55 kPa). The compression bandage should be removed if used. The limb should be pale, and pulses should not be palpable.

Infuse the anesthetic via the small catheter of the affected limb. Most authors recommend diluting standard 1% lidocaine with equal parts normal saline to create a 0.5% (5 milligrams/mL) solution. The amount infused varies according to physician preference in the range of 1.5 to 3.0 milligrams/kg (3 to 6 mL of the 0.5% lidocaine solution for every 10 kg of body weight).¹¹⁴ Onset of anesthesia is usually within 5 minutes. If inadequate anesthesia occurs when using a minidose (1.5 milligrams/kg), infuse additional lidocaine up to 3 milligrams/kg. If adequate anesthesia is not obtained with the maximum dose of lidocaine, infuse additional normal saline to help circulate the anesthetic.

The patient may report a sensation of warmth or cold, and the skin will become mottled. The smaller nerve fibers are affected first, causing a reduction in pain and temperature sensation followed by loss of touch, deep pressure, and, finally, motor function. An ideal Bier block will provide complete anesthesia and muscle relaxation, but patients may retain varying degrees of intact touch, deep pressure sensation, and motor function. Remove the IV in the affected extremity once adequate analgesia is obtained. Many patients will describe pain or pressure at the tourniquet site, usually within 30 minutes or so. This is handled by reinflating the previously deflated distal cuff. After ensuring that the distal cuff is inflated to the proper level and will hold pressure, the proximal cuff is slowly deflated. Dexmedetomidine mixed with the local anesthetic can also be used to control the pain of tourniquet inflation and provide postprocedure analgesia.¹¹⁷

The cuff should not be released until a minimum of 30 minutes after the initial lidocaine infusion; premature release of the cuff increases the chance of systemic toxicity from the anesthetic. Upon completion of the procedure, the pneumatic tourniquet should be cycled by lowering the cuff pressure for 5 to 10 seconds and then reinflating it for 1 to 2 minutes. This cycling should be repeated three to five times to prevent any possible bolus of anesthetic into the central circulation. Additional analgesia is usually required after completion of the procedure because anesthesia rapidly dissipates after release of the tourniquet. The patient should be monitored for approximately 30 minutes to ensure that no adverse reaction to the anesthetic has occurred.¹¹⁴