An ultrasound-guided nerve block increases the likelihood of successful peripheral nerve blockade and reduces the risk of complications but requires equipment and trained personnel.
The use of point-of-care ultrasound in peripheral nerve blocks has improved the success and safety of procedures that were previously dependent on only anatomical landmarks (1). By using real-time visualization, clinicians can precisely identify the target nerve and adjacent structures, enabling a safer, more controlled, and more effective deposition of local anesthetic than traditional blind anatomic landmark-only techniques.
Ultrasound guidance can minimize the risk of inadvertent needle placement, nerve injury, and other complications (eg, hematoma formation, vascular puncture) while optimizing block efficacy and anesthetic spread. Ultrasound-guided nerve blocks are used in a variety of clinical settings to provide regional anesthesia for various surgical procedures, and it is also being used for pain control of acute injuries (2). Ultrasound-guided nerve blocks can be used in many locations throughout the peripheral nervous system, ranging from the intercostal nerves for chest wall pain to the femoral and sciatic nerves for lower-extremity procedures or injuries.
Indications to Ultrasound-Guided Nerve Blocks
Regional anesthesia for surgical procedures
Acute pain management
Contraindications to Ultrasound-Guided Nerve Blocks
Absolute contraindications
History of allergy to the anesthetic agent
Relative contraindications
Infection in the path of needle insertion: Use procedural sedation or a different means of anesthesia.
Coagulopathy*: When feasible, correct prior to procedure or use a different means of analgesia.
* Anticoagulant medications (eg, for atrial fibrillation) increase the risk of bleeding with nerve blocks, but this must be balanced against the increased risk of thrombosis (eg, stroke) if anticoagulation is reversed. Discuss any contemplated reversal, first with the clinician managing the patient's anticoagulation and then with the patient.
Complications to Ultrasound-Guided Nerve Blocks
Adverse reaction to the anesthetic (eg, allergic reaction to the anesthetic [rare] or to methylparaben [a preservative]; see Local anesthesia for laceration treatment)
Hematoma
Neuritis
Spread of infection, by passing the needle through an infected area
Equipment for Ultrasound-Guided Nerve Blocks
Gloves (sterile gloves are not required)
Personal protective equipment as indicated (eg, face mask, safety glasses or face shield, cap and gown)
Syringe (eg, 10 mL) and needle (eg, 25 or 27 gauge, 3.5 cm long) for anesthetic injection
Ultrasound machine with high-frequency (eg, 7.5 MHz or higher) linear array probe (transducer); probe cover (eg, transparent sterile dressing, single-use probe cover); sterile, water-based lubricant, single-use packet (preferred over multi-use bottle of ultrasound gel)
* Local anesthetics are discussed in Local anesthesia for laceration treatment.
Step-by-Step Description of Ultrasound-Guide Nerve Blocks
Set the ultrasound machine to 2-D mode or B mode. Adjust the screen settings and probe position if needed to attain an accurate left-right orientation. This almost always means orienting the side-mark on the probe to the operator's left side (corresponding to the left-sided marker dot/symbol on the ultrasound screen).
Wear gloves and use appropriate personal protective equipment.
Identify injection site of target nerve.
Cleanse the injection site with antiseptic solution.
Place a skin wheal (shallow intradermal injection) of anesthetic, if one is being used, at the injection site.
Cover the probe tip with a layer of gel, then cover the tip with a sterile transparent dressing tightly (to eliminate air bubbles underneath). Apply sterile lubricant to the covered tip.
Place the probe tip to identify the nerve in the transverse plane,
Adjust the gain on the console so that the blood vessels are hypoechoic (appear black on the ultrasound screen) and the surrounding tissues are gray. Nerves appear as an echogenic (white), honeycombed, triangular shape, often adjacent to an artery.
Adjust depth to visualize the nerve in the middle of ultrasound screen.
Slide the probe along the nerve to identify its course.
Insert the needle and slightly tilt/rotate the probe to view the needle on the ultrasound screen (an in-plane, longitudinal image).
Maintain the entire longitudinal needle image on the screen while advancing the needle until the tip lies close to the nerve.
Inject a small test dose of anesthetic (about 0.25 mL) to see whether it spreads around the nerve. If not, move the needle closer to the nerve and inject another test dose.
When the needle tip is properly positioned, inject 1 to 2 mL of anesthetic solution to further surround the nerve. If necessary, reposition the needle tip and inject more small amounts; however, the donut sign—nerve completely surrounded by anesthetic—is not required.
Warnings and Commons Errors for Ultrasound-Guide Nerve Blocks
Ultrasound may not visualize very small or deep nerves, increasing the risk of accidental puncture of nerves, surrounding tissues or blood vessels.
Needle artifacts and other image complexities (eg, acoustic shadowing) can lead to confusion and errors in nerve identification.
Tips and Tricks for Ultrasound-Guide Nerve Blocks
Ensure proper ergonomics for both you and the patient to maintain sterile technique and good visualization of the ultrasound image.
Use needle visualization techniques like "in-plane" (longitudinal) or "out-of-plane" (transverse) approaches to confirm needle-tip location throughout the procedure.
Use small "back and forth" motion of the needle to assist with needle-tip visualization.
Watch for signs of discomfort, such as severe pain or paresthesia, which may signify nerve puncture.
References
1. Bhoi S, Chandra A, Galwankar S: Ultrasound-guided nerve blocks in the emergency department. J Emerg Trauma Shock 3(1):82-88, 2010. doi: 10.4103/0974-2700.58655
2. Brown JR, Goldsmith AJ, Lapietra A, et al: Ultrasound-guided nerve blocks: Suggested procedural guidelines for emergency physicians. POCUS J 7(2):253-261, 2022. doi: 10.24908/pocus.v7i2.15233
