The ulnar nerve runs adjacent to the ulnar artery in the ulnar (medial) direction. Position the linear ultrasound at the wrist over the ulnar artery. Scan proximally until the nerve separates from the artery in the ulnar direction in the mid- to proximal forearm (see Figure 5). For a more comfortable position to perform an in-plane ultrasound-guided ulnar nerve block, consider having the patient abduct the arm and flex the elbow to 90 degrees, with the elbow resting on the stand.8
Performing the Block
Before your block, perform and document an appropriate neurovascular exam. After prepping the skin with antiseptic solution, use a local anesthetic to make a skin wheal at your chosen injection site. With a sterile transducer cover, insert your needle using an in-plane approach for continuous direct needle visualization. For the median nerve block, enter from whichever side is most comfortable/natural (see Figure 3). For the radial nerve block, enter the skin from the radial (lateral) aspect of the probe (see Figure 4). For the ulnar nerve block, enter from the ulnar (medial) aspect of the probe (see Figure 5).
Once the needle tip is visualized to be adjacent to the nerve, slowly inject 2 to 5 mL of anesthetic into the fascial plane containing the nerve. You should see hypoechoic fluid gradually surrounding the nerve. Be careful not to insert your needle or inject anesthetic into the nerve sheath itself. Also, be careful to avoid vascular structures while inserting and removing your needle. While we recommend that novice providers use an in-plane approach for all regional nerve blocks, the median presents an opportunity to practice employing an out-of-plane approach since it doesn’t lie as close to major vascular structures as the radial and ulnar nerves.
After the Block
After performing the forearm nerve block, mark the affected extremity with the date, time, and type of block performed. Communicate with the nurse(s), other providers, and any relevant consultants that a block was performed. Of note, if consultants are to be involved in the acute care of your patient’s injury, a clear discussion regarding regional anesthesia should occur prior to performing your block. Lastly, reassess your patient to ensure adequate analgesia and assess the efficacy of your block. Be sure to reassess and document repeat neurovascular examinations.