Background

An ultrasound-guided ulnar nerve block can be performed to give surgical anesthesia or analgesia to the ulnar side of the hand and the little finger and the ring finger. It is most helpful in ulnar nerve distribution operations but can also use as an add-on to radial and median nerve blocks for complete hand anaesthesia, or as a supplementary to inadequately effective brachial plexus blocks. As a means of anesthesia, it is used in patients who cannot be given sedation for procedures such as fracture reductions and is also very useful in the management of acute pain in patients with burns among others. For repeated lacerations that would need suturing, regional anesthesia techniques help in reducing the total volume of local anesthetic while providing adequate surgical anesthesia to the areas. 

Indications

An ulnar nerve block can also be used as an alternative to the incomplete brachial plexus blocks especially with the interscalene technique. The study also revealed that the infraclavicular blocks supplemented with ulnar, median, and radial nerve blocks can produce faster onset of the blocks and increased block reliability. 

For surgical procedures of the ring or middle finger, that is the reason why a median nerve block is recommended since it supplies medial half of the ring finger, and the dorsal aspect of the terminal phalanges of the ring and middle fingers. An ulnar nerve block together with a median nerve block can be useful when making an arteriovenous fistula. 

This block is traditionally used where there are emergency services. Several investigations have shown the feasibility of performing ultrasound-guided radial, median, and ulnar nerve blocks within emergency departments.  

For chronic pain, it becomes challenging to address ulnar nerve neuropathy and poor outcome of transposition by ulnar nerve by using a peripheral nerve stimulator. A diagnostic ulnar nerve block is carried out prior to electrode implantation in most of the cases. 

Contraindications

Contraindications include patient’s refusal, infection in the area where the block is to be administered. However, some contraindications include failure or refusal to obtain vasoconstriction, and performing a nerve block is not advisable for procedures that may involve the use of a tourniquet for an extended period. For most patients presenting ulnar nerve neuropathy, the use of nerve blocks should be discouraged except for diagnostic purposes only. 

Outcomes

Ulnar nerve block is useful in managing hand and finger lacerations; less local anaesthesia is needed than with a brachial plexus block, and complications are rare. It is most effective when used for short surgeries that may take 2 to 3 hours in the emergency room or the operating theatre. Although issues can arise, these are less common than in traditional open surgeries as the rate of adverse events are less than 1 to 3 percent. The most frequently occurring kind is the anatomical variant in which the ulnar nerve has been partially divided. 

Equipment

For an ultrasound-guided ulnar nerve block, the following supplies are needed: 

Local anaesthetic: 3 to 5 mL of 0. 5% bupivacaine or ropivacaine for more prolonged blockade or 3-5 ml 2 % lidocaine or 1. 5% mepivacaine for short lasting blocks. 

Ultrasound scanner and high-frequency linear transducer with a frequency above 8 MHz 

Sterile ultrasound gel 

Bevel block needle- Short 

10 mL syringe 

Skin antiseptic solutions like povidone iodine solution or 2% chlorhexidine solution 

Patient preparation

Before proceeding, the clinician should seek the consent to be recorded from the patient. Ensure that the patient is positioned in a way the volar area of the affected arm is most exposed. This can be done with the forearm and hand placed on a flat surface or by bringing the arm to the right angle at the elbow while laying the forearm on the back with palms down on a stack of towels. The latter position facilitates the steadying of the arm on the towels while holding the ultrasound probe. Wash the area over the intended injection site with povidone iodine or 2% chlorhexidine. Place a sterile cover over the high frequency linear ultrasound probe and then make sure that a gel is applied to the surface of the cover. Squeeze the following local anaesthetic into a syringe of your preference. Make sure the patient is well observed, and intralipid 20% should be nearby in case the pt has systemic toxicity from the local anesthetic used. 

Patient position

Above or Below the Elbow Approach: 

Supine Position: The patient is in a supine position and one of the patient’s arms is raised with slight abduction at the shoulder and flexion at the elbow. By fixing the forearm in pronation or supination, additional support is available and could be done by using towels or a pillow. 

Seated Position: The position of the patient is sitting, and the arm is placed in slightly flexed position in order to have proper access for working on the medial aspect of the forearm. 

Patients forearm placed in the supine position 

Step 1-Place the ultrasound probe in the horizontal plane over the medial side of the forearm slightly proximal to the medial epicondyle. 

Step 2-Identify the ulnar nerve running as a white structure, resembling a honeycomb just beneath the flexor carpi ulnaris muscle. 

Step 3-Identify the ulnar nerve and trace it distally ending approximately 3 to 4 cm proximal to the cubital tunnel. 

Step 4-Pass the block needle in a lateral-medial fashion while always keeping the needle tip in view. 

Step 5-Stab the needle tip to a position just beneath the ulnar nerve. 

Step 6-It is advisable to perform negative aspiration as a way of confirming that the needle tip is not within a blood vessel if one is intended. 

Step 7-Every 1-2 mL of a local anaesthetic is injected, and the position of the needle tip may be changed. 

Step 8-In the case of the subcutaneous anaesthesia, repeat the process of aspiration and injection until distribution of the local anaesthesia is around the nerve is enough. 

Step 9-Do not administer intraneurally: infuse the drug intravenously rather than directly into the nerve. When the needle tip appears to be in the nerve or when the patient complains of intense pain during injection, one should not proceed and should withdraw the needle. 

Ulnar Nerve Block 

Approach considerations

The first and most critical clinical justification for the block significantly determines the level at which the procedure should be performed. If the block occurs distal from the branching points, the nerve will remain blocked only partially or not at all. There are several sites that can be used to anesthetise the ulnar nerve: axillary, mid humeral, above or below the elbow, and wrist. 

Laboratory tests

• Complete blood count 
• Renal function test 
• Kidney function test 
• Blood glucose test 
• Electrocardiogram 

Complications

• Hematoma 
• Infection 
• Neuropathy 

References

Ulnar Nerve Block Techniques – StatPearls – NCBI Bookshelf (nih.gov) 

References

Ulnar Nerve Block Techniques – StatPearls – NCBI Bookshelf (nih.gov)