The examiner should locate the desired nerve at a location sufficiently separate from vascular structures (if possible), but not so deep that it cannot be reached with a standard needle.

Procedure Details

Skin prep. The skin should be cleansed with alcohol or other cleansing agent (such as chlorhexidine).

Patient monitoring. We recommend placing the patient on continuous pulse oximeter monitoring to allow the operator to be aware of the patient’s heart rate and oxygen saturation at all times.

Local anesthetic. A skin wheal of local anesthetic (1% lidocaine with or without epinephrine) should be injected with a (30-gauge) tuberculin syringe.

Syringe preparation. While the local anesthetic is taking effect, fill a syringe with 10 cc of 1% lidocaine without epinephrine. Bupivacaine should not be used by novice providers in case of inadvertent vascular puncture. In our practice, we use a standard 25-gauge, 1.5-inch needle to perform the block, and our providers often use longer-acting anesthetics once they’ve become familiar with performing these procedures.

Ultrasound-guided injection. With the transducer held in a transverse orientation at the predetermined site, introduce the needle approximately 0.5 cm laterally to the base of the transducer. For blocking the median nerve, the needle can be introduced on either side of the probe, with the location of other neurovascular structures and examiner’s hand dominance guiding the decision. For the radial nerve, the needle should be introduced on the radial side of the probe (photo 4), while for the ulnar nerve the needle should be introduced on the ulnar side of the probe (photo 5). Note that this is a description of the in-plane technique. Although we also perform these blocks using an out-of-plane technique (similar to a short-axis approach to vascular access), we have found that novice users are more successful using an in-plane technique.

The needle should be visualized from the moment it passes under the ultrasound transducer (photo 6). If the needle is not identified, the operator should not advance the needle. The needle should be removed or the probe moved to allow clear visualization of the needle. The needle should be directed from the skin entry site to the most distal border (either superficial or deep) of the nerve (photo 7). The needle should not be allowed to penetrate the actual nerve structure at any point.

Prior to injecting any anesthetic agent, draw back on the syringe to confirm that the needle is not in a vascular structure. Gently inject 0.5-1 cc of anesthetic and observe a spread of anechoic (black) fluid around the superior border of the nerve (photo 8). If anechoic fluid is not seen exiting the needle tip, the operator should not deposit more anesthetic. The probe should be adjusted to confirm that the tip of the needle is clearly visualized before more anesthetic agent is deposited. The goal is to have the anechoic fluid surround the nerve completely. Withdraw the needle towards the skin and redirect it to the area where the fluid has not reached. Repeat the injection at this site (photo 9). When complete, the nerve should be circumferentially surrounded by a layer of anechoic fluid, resembling a donut (photo 10). With the transducer, trace the nerve both proximally and distally to confirm this “donut” appearance.