Digital Nerve Block Anesthesia

E. J. Mayeaux, Jr, MD, DABFP, FAAFP
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Subject: Digital Nerve Block Anesthesia

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Introduction

Digital nerve block is commonly performed to provide anesthesia to an entire digit. Digital nerve block simultaneously anesthetizes the four digital nerves that traverse the sides of the digit. This technique provides longer duration of anesthesia than local infiltration and does not distort anatomic landmarks for digital surgery. 
Because multiple nerves are affected during the technique, this anesthesia would be more appropriately labeled “digital field block” rather than the commonly used “nerve block.” It has historically been called a “ring block” because of the circumferential infiltration of anesthetic. Administration of 1 to 3 mL of 2% lidocaine provides adequate anesthesia without use of a large volume. The great toe or thumb can also receive some additional superficial inervation proximally, and a slightly larger volume of solution may be needed for these digits. All digital blocks require some time for the anesthetic to take effect through the nerve sheath. 
Historically, physicians were instructed to insert the needle into the web space to perform digital block. The advantage of a web space injection is that the nerve can be injected at the site of bifurcation between adjoining digits. However, the blood vessels of the web space are larger than on the digit, and intravascular injection of anesthetic can more easily occur with the web space technique. 

Equipment

  • Syringes (3 or 5 mL), 2% lidocaine without epinephrine, and 25- or 27-gauge, 1.25-inch needles can be obtained from local surgical supply houses or pharmacies.

  • A suggested anesthesia tray that can be used for this procedure is listed in Appendix F.

Indications

  • Repair of digital lacerations

  • Nail procedures (e.g., ingrown nail surgery, nail bed biopsy, nail removal)

  • Incision and drainage of abscesses (e.g., felon surgery, paronychia surgery)

  • Anesthesia for fracture or dislocation manipulation of digital orthopedic injuries

  • Tumor or cyst removal or ablation (e.g., digital mucous cysts, giant cell tumors of sheaths, warts)

Contraindications

  • Use of epinephrine added to lidocaine, especially in patients with peripheral vascular disease.

  • Use of volumes >7 mL, especially in individuals with peripheral vascular disease, Raynaud disease or the phenomenon, digital vasculitis, or impaired circulation (e.g., diabetes, scleroderma).

The Procedure

Step 1

Cross section of the digit reveals the nerves traversing laterally on each side of the digit. One nerve travels on the plantar or palmar aspect, and one is more dorsal. 
  • PITFALL: The needle should be placed just below the dermis. Injecting the anesthetic into the dermis will not produce a satisfactory nerve block.

Step 2

Prep the area with alcohol. Insert the needle near the junction of the dorsal and lateral surfaces of the digit. Slide the needle along the lateral surface, injecting as the needle tip is withdrawn back to the insertion site. 

Step 3

Without pulling the needle tip out of the skin, redirect the needle tip along the dorsum of the digit and again administer the anesthetic as the needle is withdrawn. 

Step 4

Administer the anesthetic along the opposite sides of the digit in a similar manner. 
  • PITFALL: In large digits or digits that do not develop good anesthesia at the tip, insert the needle near the junction of the volar and lateral surfaces of the digit and inject additional lidocaine along the volar surface.

  • PITFALL: Do not attempt any assessment of anesthetic efficacy or the actual procedure until the block has had 5 minutes to work. Many novice and impatient physicians continue to add volume when a few more minutes of time would produce the desired effect, and the additional volume does not hasten the anesthesia.

Step 5

Smaller digits can be injected through a single insertion site. Enter the skin at the midline of the digit distal to where the toe joins the foot. Slide the needle down one lateral surface, injecting as the needle tip is withdrawn back to the insertion site. Without pulling the needle tip out of the skin, redirect the needle tip down the opposite side of the digit and administer the anesthetic as the needle is withdrawn. 

Step 6

An alternate technique of digital block inserts the needle laterally into the base (proximal portion) of the digit, about halfway between the proximal interphalangeal joint and metacarpal interphalangeal joint. 

Step 7

Insert the needle to the bone, and infuse anesthetic. Angle the needle volarly and dorsally. Repeat this technique on the opposite side. 

Complications

  • Increasing rates of vascular compromise can be observed with circumferential infiltration, especially if volumes >7 to 8 mL are administered to the smaller digits. Use of 3- or 5-mL syringes can help avoid the temptation to deliver larger volumes.

  • Impaired digital circulation can also occur if an individual suffers from vasospastic disease such as the Raynaud phenomenon or if the digit is markedly swollen before infiltration.

  • Despite evidence for the safety of the practice, it is still advisable to avoid the addition of epinephrine to lidocaine for use on the digits.

Pediatric Considerations

Children older than 6 years are dosed like adults except that the maximal dose is based on weight. Children 6 months to 3 years have the same volume of distribution and elimination half-life as in adults. Neonates have an increased volume of distribution, decreased hepatic clearance, and doubled terminal elimination half-life (3.2 hours). The recommended maximal dose for lidocaine in children younger than 6 years is 3 to 5 mg/kg, and 7 mg/kg when combined with epinephrine

Postprocedure Instructions

Have the patient report redness, itching, or shortness of breath, which may signal an allergic reaction to lidocaine

Coding Information and Supply Sources

No current procedural terminology (CPT) code exists for digital nerve block. The service is included in the reporting for the procedure for which it is performed (e.g., laceration repair, biopsy service). 

Bibliography

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