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Introduction To Regional Anesthesia And Peripheral Nerve Blocks

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Authors

Victor Huang, MD, CAQ-SM
Assistant Professor
Department of Emergency Medicine
New York Presbyterian Queens, Weill Cornell Medical College

Summary

  • In the Emergency Department, peripheral nerve blocks offer several advantages over local infiltration of anesthetics, systemic analgesia and procedural sedation. 
  • The use of ultrasound guidance significantly improves the efficacy of peripheral nerve blocks and decreases the risk of intravascular and intraneural injection. 
  • Providers performing local anesthetic injections should always be aware of the risks of this procedure, especially LAST, and should have resuscitation equipment and intravenous lipid emulsion therapy available.

Introduction

  • Regional anesthesia is the use of local anesthetics to block peripheral nerves in order to reduce sensation in a particular area of the body. It is important for Emergency Medicine providers to be familiar with this modality of pain management to facilitate procedures and optimize patient comfort. 
  • Indications for Regional Anesthesia
    • Orthopedic procedures: fracture reduction, dislocation reduction, and tendon repair.
    • Wound care: adequate examination, hemostasis, irrigation, debridement, and laceration repair.
    • Dental procedures, tooth pain, occipital neuralgia, and facial lacerations.
  • Contraindications for Regional Anesthesia
    • Absolute contraindications: infection at the injection site, local anesthetic allergy [1] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048
    • Relative contraindications: pre-existing neuropathy and patients taking anticoagulants [2] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048
    • Discretion of consulting physicians who wish to maintain a thorough neurological examination of the affected area.
    • In patients that are at high risk for acute compartment syndrome (i.e. tibia fracture in adults, radius-ulna fracture in children), peripheral nerve blocks are strongly discouraged.
  • Benefits of Regional Anesthesia
    • Regional anesthesia is a safe and effective alternative to other pain management strategies including systemic analgesia, procedural sedation, and local infiltration for an array of painful conditions and procedures [3] Bhoi S, Chandra A, Galwankar S. Ultrasound-guided nerve blocks in the emergency department. J Emergencies, Trauma Shock. 2010;3(1):82-88. doi:10.4103/0974-2700.58655 [4]Canders CP, Morales DA, Sha SW. Ultrasound-guided Nerve Blocks in the Emergency Department. Relias Media. Published March 2018. Accessed August 2, 2020. … Continue reading

Complications

  • Risks of peripheral nerve blocks include vascular injury, intravascular injection, nerve injury, intraneural injection, infection and hematoma.
  • Local Anesthetic Systemic Toxicity (LAST)
    • LAST is a side effect of intravascular injection or injection exceeding maximum dose of a local anesthetic that results in a spectrum of issues due to sodium channel blockade [5]Canders CP, Morales DA, Sha SW. Ultrasound-guided Nerve Blocks in the Emergency Department. Relias Media. Published March 2018. Accessed August 2, 2020. … Continue reading [6] El-Boghdadly K, Pawa A, Chin KJ. Local anesthetic systemic toxicity: Current perspectives. Local Reg Anesth. 2018;11:35-44. doi:10.2147/LRA.S154512
    • Mild symptoms include nausea, tinnitus, perioral tingling, and metallic taste. Severe symptoms include seizures, bradycardia, dysrhythmias, respiratory depression and cardiac arrest [7]Canders CP, Morales DA, Sha SW. Ultrasound-guided Nerve Blocks in the Emergency Department. Relias Media. Published March 2018. Accessed August 2, 2020. … Continue reading [8] El-Boghdadly K, Pawa A, Chin KJ. Local anesthetic systemic toxicity: Current perspectives. Local Reg Anesth. 2018;11:35-44. doi:10.2147/LRA.S154512
    • Treatment of LAST: Stop the injection, IV Lipid Emulsion Therapy, management of seizures, cardiopulmonary support
      • Initial management includes stopping the injection of local anesthetic and stabilizing the patient’s airway, breathing, and circulation. 
      • Intravenous lipid emulsion therapy 20% should be administered in an initial bolus of 1.5 mL/kg and then followed by an infusion of 0.25 mL/kg/min [9] El-Boghdadly K, Pawa A, Chin KJ. Local anesthetic systemic toxicity: Current perspectives. Local Reg Anesth. 2018;11:35-44. doi:10.2147/LRA.S154512
      • Seizures should be treated with benzodiazepines. Standard ACLS algorithm should be utilized for cardiac arrest.
  • Neuropraxia
    • Nerve blocks may be associated with acute and/or chronic nerve injuries. This may occur with or without penetration of the epineurium and injury to the neurons within the sheath. This risk is lessened by the use of ultrasound guidance. [10] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 It is not possible for the emergency medicine physician to distinguish between a successful nerve block and nerve injury at the time of the procedure.
  • Hematoma
    • Bleeding may occur due the injury to capillary beds or blood vessels, if the patient is anticoagulated or on antiplatelet therapy, or if the patient has a coagulopathy. In some cases, the bleeding can be controlled with compression (i.e. fascia iliaca block, etc) while others are more challenging (i.e. supra- or infraclavicular block).
  • Infection
    • As with all procedures, there is a risk of infection. Using sterile precautions, this risk is considered low. Proceduralists should consider overlying or systemic infection when making the decision to proceed.

Techniques

  • Landmark vs Ultrasound Guidance
    • Landmark-based techniques utilize anatomical landmarks to guide the location of peripheral nerves, as well as fascial clicks and loss of resistance to guide blocks. These techniques are limited to peripheral nerves that have reliable landmarks to guide injection [11] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 It is important to aspirate before injecting local anesthetic to avoid intravascular injections, and to monitor the patient for sharp pain or paresthesia that may be indicative of intraneural injection.
Illustration of In-Plane vs Out-of-Plane technique.
    • Ultrasound guidance for peripheral nerve blocks has significantly improved the safety and efficacy of these procedures because the provider can directly visualize the nerve, the adjacent vascular structures, and the needle trajectory [12]Canders CP, Morales DA, Sha SW. Ultrasound-guided Nerve Blocks in the Emergency Department. Relias Media. Published March 2018. Accessed August 2, 2020. … Continue reading. In comparison to landmark-based blocks, ultrasound-guided blocks have a lower risk of intravascular injection and a higher success rate with more rapid control of pain and decreased amount of anesthetic required [13] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 [14]Canders CP, Morales DA, Sha SW. Ultrasound-guided Nerve Blocks in the Emergency Department. Relias Media. Published March 2018. Accessed August 2, 2020. … Continue reading
  • Ultrasound-Guided Technique
    • The vast majority of ultrasound-guided peripheral nerve blocks are best performed with an in-plane approach with the nerve visualized in short-axis. The transducer should be placed in the transverse plane, short-axis to the nerve in order to visualize a cross-sectional image of the nerve as well as the adjacent vascular structures that should be avoided [15] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 [16] Jacobson JA. Interventional Techniques. In: Fundamentals of Musculoskeletal Ultrasound. 3rd ed. Philadelphia,PA: Elsevier; 2018:407-442. [17] Brown JM, Yablon CM, Morag Y, Brandon CJ, Jacobson JA. US of the peripheral nerves of the upper extremity: A landmark approach. Radiographics. 2016;36(2):452-463. doi:10.1148/rg.2016150088
  • The in-plane approach allows the provider to continuously visualize the entire length of the needle throughout the procedure in order to guide the tip towards the nerve and avoid the vascular structures [18] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048

Equipment

  • US Probe: A high-frequency linear transducer, 10 MHz or greater, is the optimal probe to use because the majority of peripheral nerves are superficial [19] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 [20]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading. The curvilinear probe may be used for a variety of blocks in the lower extremity.
  • Optimize the image by placing the structure of interest in the center of the screen and adjusting the gain to visualize the neurovascular bundle and the surrounding structures [21] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048
linear probe
Linear transducer is preferred.
  • Local anesthetics are medications that block sodium channels and result in neuronal blockade of sensory/afferent nerves (analgesia) and motor/efferent nerves (paralysis).
  • The onset of action, duration of action, and maximum dosage of common local anesthetics can be found in Table 1.
  • Choice of Anesthetic Agent
    • Lidocaine: rapid onset of action and shorter duration of action. Best utilized for painful procedures in the Emergency Department.
table of local anesthetics
Characteristics of local anesthetics (click to enlarge).[22]Kouba, David J., et al. “Guidelines for the use of local anesthesia in office-based dermatologic surgery.” Journal of the American Academy of Dermatology 74.6 (2016): 1201-1219.
      • Epinephrine is a vasoconstrictor and a common additive to local anesthetics that prolongs the duration of anesthesia and helps control bleeding.
    • Bupivacaine: long duration of action of 2 – 6 hours, but has the highest incidence of LAST [23]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading
    • Ropivacaine: rapid onset with long duration of action of 2 – 8 hours with fewer cardiovascular and CNS effects than bupivacaine [24]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading While commonly used by anesthesia, this medication is not routinely available in the emergency department.
  • Materials
    • Sterile ultrasound probe cover and gel
    • Sterile gloves, sterile field 
    • Chlorhexidine or betadine to sterilize the site
    • Needles
      • 18 gauge needle to withdraw the medication from the vial
      • 22 – 27 gauge needle to inject
      • The length of the needle depends on the depth of the peripheral nerve that is being targeted. A 1.5-inch needle is most commonly used [25]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading [26]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading
    • Syringe
      • The size of the syringe depends on the amount of local anesthetic to be injected. A 5 – 10 cc syringe is most commonly used [27]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading
    • Local anesthetic
      • 2 – 5 cc of local anesthetic per nerve block [28] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 [29]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading
      • In some cases, you may wish to give a larger volume of fluid (i.e. fascia iliaca block) and may dilute your local anesthetic with sterile water or saline.
      • Local anesthetic + appropriate size syringe
        • 15-25mL of anesthetic is appropriate for most adults. 
        • For most emergency departments, lidocaine will be the best choice due to availability, operator comfort, and length of block. We recommend 20 mL of lidocaine 1% as a good reference point. For a 70kg adult, the max dose is approximately 28 mL. 
    • Extension tubing
    • Assistant (to help with injection)
    • Resuscitation equipment should be readily available (code cart, airway equipment, ACLS medications, lipid emulsion therapy) [30]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading

Nerve Ultrasound Principles

  • Nerves are made up of multiple fascicles which are each surrounded by perineurium. Bundles of these fascicles make up a single nerve, which is surrounded by epineurium. When visualized in cross-section, this creates a typical cable or “honeycomb” appearance on ultrasound, made up of hyperechoic epineurium surrounding a bundle of hyperechoic perineuria wrapping hypoechoic round areas. In longitudinal plane, the nerve appears as a long slim structure with multiple hyperechoic parallel lines representing perineurium. [31] Silvestri E, Martino F, Puntillo F. Ultrasound-guided peripheral nerve blocks. In: Silvestri E, Martino F, Puntillo F, eds. Ultrasound-Guided Peripheral Nerve Blocks. ; 2018. doi:10.2199/jjsca.28.103
  • Nerves are usually in between fascial planes, including often surrounded by fascial paraneurium. More effective anesthesia is achieved when local anesthetic is injected in between epineurium and paraneurium. This can be achieved by visualizing the needle approaching the nerve in a tangential approach to avoid direct intraneural penetration, then using a loss of resistance sensation to indicate entrance into the paraneurium. The optimal spread of local analgesia would then form a circumferential spread around the nerve between the paraneurium and epineurium. [32] Ghisi D, Delaunay L, Fanelli A. Use of ultrasound for lower extremity. Curr Opin Anaesthesiol. 2014;27(5):528-537. doi:10.1097/ACO.0000000000000119

General Procedure

  • Preparation
    • Obtain a brief history from the patient including drug allergies, medications, and past medical history, especially any complications from anesthesia during previous surgeries [33]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading.  Document a detailed neurovascular examination before performing the nerve block [34]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading 
    • Consent the patient for the procedure including the risks, benefits and alternatives. The patient should be aware that additional injections or pain management modalities may be needed if the block does not provide adequate anesthesia [35]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading.
  • Positioning the Patient and Ultrasound Machine
    • Positioning of the patient, provider and ultrasound machine should be optimized for image quality and the comfort of the patient and provider. Generally, the site of injection should be positioned in between the provider and the ultrasound machine so that the provider can visualize both physical anatomy and ultrasound anatomy in their line of sight. The probe marker should be positioned so that movement of the transducer relative to the structure of interest correlates with the same direction of movement on the screen.
  • Pre-Scan / Find Anatomical Landmarks
    • Landmark-based: identify the anatomical landmarks, locate pulsatile arteries that should be avoided, and mark the optimal site of injection. 
    • Ultrasound-guided: place the transducer in short-axis to the nerve and scan proximal and distal to confirm the anatomy. Identify the optimal location for the injection, ideally where the nerve is separate from the arteries and veins, which can be confirmed with color flow Doppler. Mark the site of injection. [36] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048
  • Sterilization
    • Prep the site with an antiseptic solution (i.e., Chlorhexidine) and allow it to fully dry to optimize its effect [37]Kelly JJ, Younga J. Regional Anesthesia of the Thorax and Extremities. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges’ Clinical Procedures in Emergency Medicine and Acute Care. … Continue reading
  • Ultrasound Visualization
    • Using a sterile probe cover, find the nerve and guide the needle in an in-plane fashion.
  • Needle Trajectory and Insertion
    • The needle should puncture skin and approach the nerve on the opposite side of the adjacent vascular structures [38] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048
  • Local Anesthetic Injection
    • When the needle tip is adjacent to the nerve, slowly inject the local anesthetic in order to surround the nerve with the hypoechoic fluid [39] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 [40]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading Aspirate before injecting to avoid intravascular injection. Be careful to either monitor the patient for pain and paresthesia, or visualize the needle tip with ultrasound to avoid injecting directly into the nerve sheath [41]Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading.
    • Watch for hydrodissection in the tissue plane of interest. Be aware that back pressure from the anesthetic may push your needle out of the tissue area of interest and require re-adjustment.
  • Post-Procedure
    • Assess the patient to determine the efficacy of the peripheral nerve block and perform a repeat neurovascular examination [42] Wroe P, Nagdev A. How to Perform Ultrasound-Guided Forearm Nerve Blocks to Provide Non-Drug Pain Relief for Acute Injuries. ACEP Now. Published October 2016. Accessed August 4, 2020. … Continue reading. After the procedure, warn the patient about the duration of anesthesia of the affected area and instruct them to protect it from heat or injury [43] Capek A, Frca M, Dolan J, Ffarcsi Edra P. Ultrasound-guided peripheral nerve blocks of the upper limb. Contin Educ Anaesth Crit Care Pain. 2014;15(3):160-165. doi:10.1093/bjaceaccp/mku048 Be certain to communicate to any consulting services and nursing staff regarding the nerve block including the duration of effects and possible complications.

Pearls & Pitfalls

  • Avoid performing nerve blocks if the patient has an infection at the site or allergy to the anesthetic
  • Double check the amount of local anesthetic to make sure it is below the maximum weight-based dose (see Table 1).
  • Preparation is key! Make sure you have positioned the patient to optimize the success of the nerve block and have all the necessary materials readily accessible.
  • Monitor the patient for adverse reactions to the injection like LAST, which is potentially life-threatening.

References[+]