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Caleb P. Canders, MD, Department of Emergency Medicine, University of California, Los Angeles
David A. Morales, MD, Department of Emergency Medicine, University of California, Los Angeles
Sophie W. Sha, University of California, Los Angeles
Andrew Kitchen, MD, Department of Emergency Medicine, Carolinas Medical Center, Charlotte, NC
Michael A. Gibbs, MD, FACEP, FAAEM, Professor and Chair, Department of Emergency Medicine, Carolinas Medical Center, Charlotte, NC
Pain management is an important but often challenging task for emergency providers. Oral and intravenous analgesics have inherent risks, which may limit their use in certain populations, such as the elderly. Nonsteroidal inflammatory drugs, for example, can cause kidney injury and gastrointestinal bleeding and are associated with high rates of hypersensitivity reactions.1,2 Opiates can cause sedation, apnea, and hypotension.3,4 In addition, the use of opiates in the emergency department (ED) has been linked to subsequent misuse, addiction, and overdose.5-7 As a result of concerns regarding the safety profiles and addiction potential of analgesics, patients often receive suboptimal pain management in the ED.8,9
Ultrasound-guided nerve blocks offer effective and safe alternatives to systemic analgesics to manage pain in the ED. Studies have shown that with minimal training, emergency providers can perform nerve blocks successfully in both pediatric and adult patients in the prehospital and ED settings.10-18 Ultrasound-guided nerve blocks also can be performed quickly and require only basic equipment that is already available in most EDs. Most importantly, the administration of a nerve blocks for some injuries (e.g., hip fractures) is associated with improved analgesia, decreased intravenous narcotic use, and improved morbidity and mortality when compared to use of intravenous analgesics alone.19,20
This article reviews the literature supporting the use of ultrasound-guided nerve blocks in the ED and describes how to perform some of the most basic nerve blocks, including forearm (median, radial, and ulnar nerves), femoral, and posterior tibial nerve blocks. Additional ultrasound-guided nerve blocks that have been performed in the ED and described in the literature will not be reviewed here. It is assumed that the reader has a basic understanding of ultrasound, although some emergency providers may require additional ultrasound training prior to performing a nerve block independently. By increasing the awareness of and performance of ultrasound-guided nerve blocks in the ED, either alone or in conjunction with other pain management modalities, it may be possible to decrease the use of opiates and other systemic analgesics for pain control.
The use of ultrasound when performing nerve blocks allows the emergency provider to visualize the nerve and its adjacent vascular structures, thereby targeting the injection of the anesthetic and avoiding adjacent blood vessels. Compared to “blind,” landmark-based techniques, ultrasound-guided nerve blocks have been shown to have higher rates of successful sensory block, decreased amounts of anesthetic required to achieve effect, less damage to vascular structures, and faster pain control.12,21-25 The use of ultrasound also helps emergency providers to perform nerve blocks in areas without adequate anatomic landmarks, such as an ulnar nerve block in the mid-forearm.26
Ultrasound-guided nerve blocks are safe and effective in most patients, including children.11,17,18 In addition, given that they require minimal supplies, ultrasound-guided nerve blocks can be performed in a variety of settings, including combat and disaster settings.13-16 One important contraindication to nerve blocks is an allergy to local anesthetic. In addition, nerve blocks should be performed only on awake and alert patients. (See Table 1.) Patients should understand the risks and benefits of the nerve block, provide consent, and be able to report any pain or paresthesia during the nerve block, which suggests the nerve has been punctured and the needle should be redirected. Depending on the injury, some patients also may be predisposed to compartment syndrome and, therefore, should be able to report unpredicted changes in sensory function. Finally, some blocks are technically challenging and require that the patient remain still and follow instructions.
Prior to starting any nerve block, adjust the height of the bed and position the patient and ultrasound machine to facilitate the procedure. (See Table 2 and Figure 1.) Identify the nerve on ultrasound at the anticipated site of injection and then follow the nerve both proximally and distally. On ultrasound, nerves typically appear as hypoechoic (dark) fascicles surrounded by hyperechoic (bright) connective tissue, also described as a “honeycomb” appearance. (See Figure 2.) For most nerve blocks, we recommend placing a local skin wheal of a rapid-onset anesthetic (e.g., lidocaine) using a 25- to 30-gauge needle over the anticipated point of entry for the block. The skin wheal usually is placed just adjacent to the ultrasound probe, and sterile technique should be used.
Most peripheral nerve blocks are performed using an in-plane technique to ensure visualization of the entire needle, including its tip, throughout the procedure. In the in-plane technique, the provider holds the ultrasound probe in his/her nondominant hand, resting the palm on the patient’s skin for stability. A skin wheal of local anesthetic is placed just medial or lateral to the probe, usually on the opposite side of any vascular structures to avoid accidental puncture during the procedure. Using his or her dominant hand, the provider advances the needle through the skin wheal and toward the nerve. (See Figure 3.) The angle of entry will depend on the depth of the nerve. To avoid injury to neurovascular structures, the needle should not be advanced unless the tip is visualized, which is best achieved when the bevel faces up toward the transducer.27
The out-of-plane technique is reserved for nerve blocks that are restricted by the patient’s anatomy, such as the posterior tibial nerve located behind the medial malleolus. This technique may be more familiar to emergency providers, as it is the technique used most commonly for ultrasound-guided central line placement. In the out-of-plane technique, the provider holds the ultrasound probe with his/her nondominant hand, resting the palm on the patient’s skin for stability. A skin wheal of local anesthetic is placed just adjacent to the probe at its midline. Using his or her dominant hand, the provider advances the needle through the skin wheal and toward the nerve. In this technique, only the tip of the needle is visualized during the procedure.
Regardless of the technique used to visualize the needle during the procedure, the nerve block needle tip should always remain at least 1 cm from the nerve to avoid accidental puncture. Inadvertent injection of the nerve can lead to temporary or permanent sensory or motor deficits.28,29 Anesthetic, which appears hypoechoic (dark) on ultrasound, typically is injected above and below the nerve using “v-shaped” redirections. Redirecting the needle and injecting small aliquots of anesthetic around the nerve to obtain full circumferential spread is ideal although not required for successful sensory block. Many blocks are successful if at least half of the nerve is surrounded by anesthetic. The amount of anesthetic injected depends on the type and concentration of anesthetic used and the nerve being targeted.
Nerve blocks can be performed with one or two providers. If only one provider is available, the provider typically holds the ultrasound probe in the nondominant hand and the syringe with a blunt needle in the dominant hand. (See Figure 3.) The use of a control syringe, which allows the provider to inject and aspirate with one hand, simplifies the one-person technique.
The two-person technique generally is easier and allows the performing provider to hold the needle in the dominant hand, allowing greater dexterity during the procedure. The needle is connected via sterile tubing to a syringe, which the assisting provider controls. (See Figure 4.)
Nerve blocks usually are performed with a blunt needle to decrease the risk of intraneural and intravascular injection.28,29 Sharp needles generally are not used, although they may be safe when performing blocks on small, peripheral nerves (e.g., forearm nerves). Several types of blunt needles can be used for nerve blocks including the “blunt tip” 20- to 22-gauge block needles (ideal for superficial nerves), Quincke tip spinal needles (20- to 22-gauge), and Tuohy epidural needles (useful for deeper blocks, such as femoral nerve blocks). It is advised to use the shortest needle possible to reach the targeted nerve to avoid injury to deeper structures. A caveat to using a blunt needle is that penetrating the skin is more difficult with these needles, so it often is necessary to start perpendicular to the skin and then flatten out the needle.
The type and amount of anesthetic used to perform nerve blocks depends on the nerve being targeted and the reason for performing the nerve block. A rapid-onset, short-acting anesthetic, such as lidocaine, is adequate to facilitate quick procedures, such as suturing or reductions. Long-acting anesthetics, such as bupivacaine and ropivacaine, are preferred to manage pain associated with fractures, including hip fractures. Of note, mepivacaine and bupivacaine may cross the placenta and are contraindicated in pregnancy (Category C).30,31 See Table 3 for onset time, duration, and doses of commonly used anesthetics.
All ultrasound-guided nerve blocks require proper documentation in the medical record. This includes the clinical examinations prior to and after the nerve blocks, sterile preparation, the type and amount of anesthetic used, the time of injection (to monitor longer blocks), and any complications.
Local anesthetic systemic toxicity (LAST) occurs when a local anesthetic is injected intravascularly, leading to a dose-dependent blockade of sodium channel receptors in the cardiovascular and central nervous systems.32 Patients with mild symptoms may report oral tingling, nausea, tinnitus, or metallic taste. Patients with severe symptoms may develop seizures, bradycardia, arrhythmias, respiratory depression, and cardiac arrest. Patients with severe LAST should be treated with a 1.5 mL/kg bolus of lipid emulsion therapy, followed by a continuous infusion at 0.25 mL/kg per minute.32,33 Patients with persistent cardiovascular collapse can be given repeat boluses of lipid emulsion therapy. Seizures associated with LAST are treated with benzodiazepines.32
Hand and forearm injuries are common complaints seen in the ED. Three major nerves, the median, ulnar, and radial nerves, innervate the hand and forearm distal to the elbow. Forearm nerve blocks can be performed to manage pain associated with lacerations, burns, fractures, dislocations, and other acute injuries.10 Forearm nerve blocks do not provide anesthesia to the volar forearm or wrist and, therefore, are not indicated for most wrist fractures. Forearm nerve blocks can be performed in isolation or in combination, depending on the distribution of pain. (See Figure 5.) Studies have shown that emergency providers can learn to perform ultrasound-guided forearm nerve blocks after minimal training and as few as five supervised scans.10 Each forearm nerve blocks takes approximately 5-10 minutes to perform, and patients who receive forearm nerve blocks usually report high satisfaction with the procedure and rarely require additional analgesia.10 Similarly, forearm nerve blocks are easy to perform and have high rates of success and patient satisfaction in children.11 As a result, some EDs have incorporated ultrasound-guided nerve blocks into pain management protocols for certain forearm injuries.34,35
The median nerve lies between the flexor carpi radialis and palmaris longus tendons at the wrist. It supplies sensory innervation to the thumb, index finger, third finger, lateral aspect of the ring finger, and palm. It provides motor innervation to the thenar muscles and first and second lumbricals. Unlike the ulnar and radial nerves, the median nerve usually is not associated with a vascular structure.
Branches of the radial nerve pass over the styloid process of the radius and the anatomic snuffbox at the wrist. The radial nerve provides sensory innervation to the lateral half of the dorsum of the hand and the dorsal thumb. It provides motor innervation to the extensor muscles in the dorsal forearm. The radial nerve travels medial to the radial artery and vein.
The ulnar nerve travels deep to the flexor carpi ulnaris at the wrist. It provides sensory innervation to the fifth finger, medial aspect of the ring finger, and the medial hand. It provides motor innervation to the hypothenar and interossei muscles, adductor pollicis, deep head of the flexor pollicis brevis, and the medial two lumbrical muscles. Of note, dorsal and palmar cutaneous branches of the ulnar nerve arise 5-10 cm proximal to the wrist. As a result, ulnar nerve blocks are most successful when performed in the mid-forearm area.26,36
Ultrasound-guided forearm nerve blocks rarely have immediate or long-term complications.10 As with all nerve blocks, there are risks of introducing a skin or soft tissue infection, vascular puncture/hematoma, intraneuronal injection, and LAST.
Ultrasound-guided femoral nerve blocks are performed by emergency providers to provide analgesia for intra- and extracapsular hip fractures.37-39 Femoral nerve blocks do not provide analgesia to the lower leg or foot. Uncontrolled pain in patients with hip fractures is associated with increased delirium, poor functional recovery, and increased mortality.40-42 As a result, femoral nerve blocks are an important adjunct to pain control in patients with hip fractures and a procedure that is endorsed by the American Academy of Orthopaedic Surgeons.43 In addition, ultrasound-guided femoral nerve blocks can be performed successfully after minimal training, require little time to complete, have few complications, and usually are successful after a single attempt.38,39,44 Femoral nerve blocks also are safe and effective for controlling pain in pediatric patients with femur fractures and may reduce the need for intravenous analgesics in these patients.20,45,46 Despite this, there is evidence that the use of femoral nerve blocks is underutilized in children.47
The femoral nerve arises from the lumbar plexus (L2-4) and passes below the inguinal ligament, lying 1-2 cm lateral to the femoral artery at the inguinal crease. Inferior to the inguinal ligament, the femoral nerve bifurcates into anterior and posterior branches. The anterior branch provides sensation to the anterior, medial, and lateral thigh and hip, and motor function to the sartorious and pectineus muscles. (See Figure 9.) The posterior branch provides sensation to the knee and medial aspect of the lower leg and motor function to the quadriceps muscle.
Ultrasound-guided femoral nerve blocks rarely have immediate or long-term complications.10 Failure to penetrate the fascia iliaca is a common pitfall and may lead to inadequate pain relief. As with all nerve blocks, there are risks of introducing a skin or soft tissue infection, vascular puncture/hematoma, intraneuronal injection, and LAST. Puncture of the femoral nerve during the procedure can cause a painful, transient spasm of the quadriceps muscle (“patellar kick”). Following the procedure, the patient may have an increased risk of falls due to the weak and insensate limb.48
Ultrasound-guided posterior tibial nerve blocks provide pain relief to patients with calcaneal fractures and injuries to the plantar foot (e.g., lacerations, foreign bodies). These areas often are difficult to anesthetize with local infiltration.49,50 Posterior tibial nerve blocks alone do not provide adequate analgesia for ankle fractures; however, they can be supplemented with other regional blocks for this purpose. Compared to landmark-based techniques, the use of ultrasound-guidance when performing a posterior tibial nerve block has been shown to increase block success rate, decrease the use of adjunct analgesics, and decrease the risk of nerve injury.51-53 Given the superficial location of the nerve, posterior tibial nerve blocks are relatively straightforward to perform and are considered a “beginner-level” block by anesthesiologists.51 One potential contraindication to this type of block is compartment syndrome of the foot, which occurs in 10% patients with calcaneal fractures, because of its effect on the clinical examination.54,55 Therefore, discussion should occur with an orthopedist or podiatrist prior to performing the block.
The sciatic nerve bifurcates into the posterior tibial and common personal nerves at the popliteal fossa. The posterior tibial nerve travels with the posterior tibial artery in a neurovascular bundle between the superficial and deep compartments of the lower leg. At the ankle, this bundle passes posterior to the medial malleolus. Distal to the ankle, the posterior tibial nerve splits into the medial and lateral plantar nerves. The posterior tibial nerve is a mixed motor and sensory nerve. It provides motor innervation to the flexor muscles of the ankle and foot and sensory innervation to parts of the heel and the majority of the sole of the foot. (See Figure 11.) It does not innervate the lateral heel or extreme medial or lateral aspects of the proximal foot, which are innervated by the sural, saphenous, and sural nerves, respectively.
Ultrasound-guided posterior tibial nerve blocks rarely have immediate or long-term complications. As with all nerve blocks, there are risks of introducing a skin or soft tissue infection, vascular puncture/hematoma, intraneuronal injection, and LAST.
Other ultrasound-guided nerve blocks that have been performed by emergency providers and described in the literature include:
Pain management is an essential aspect of emergency care. However, in many circumstances, systemic analgesics are contraindicated or inadequate at controlling pain. Ultrasound-guided nerve blocks offer safe, effective, and easy-to-perform alternatives to pain control that are within the scope of practice of emergency providers. While some hospitals already have instituted pain management protocols that include ultrasound-guided nerve blocks for specific injuries, such as hip fractures and hand blast injuries, some providers may be hesitant to perform blocks because they are unfamiliar with ultrasound or have misconceptions about the efficacy of blocks.34,35 This article provides step-wise instructions on how to perform common ultrasound-guided nerve blocks, including forearm, femoral, and posterior nerve blocks, which have been shown to be easy to learn, quick to perform, and successful at managing pain, and, therefore, should be adopted into routine clinical use in the ED.
Financial Disclosure: Dr. Farel (CME question reviewer) owns stock in Johnson & Johnson. Dr. Schneider (editor), Dr. Stapczynski (editor), Ms. Light (nurse planner), Dr. Canders (author), Dr. Morales (author), Ms. Sha (author), Dr. Kitchen (peer teviewer), Dr. Gibbs (peer reviewer), Ms. Mark (executive editor), Ms. Coplin (executive editor), and Ms. Hatcher (editorial group manager) report no financial relationships with companies related to the field of study covered by this CME activity.