What is a median nerve block procedure?

A median nerve block is a procedure to anesthetize part of the palm and fingers by injecting an anesthetic solution to numb the median nerve of the forearm. The median nerve block is often performed along with an ulnar and radial nerve block to anesthetize the whole hand and the palm. The median nerve, along with the ulnar and radial nerve, provides sensation to the hand and fingers.

The median nerve provides sensation to the palm side (palmar/volar aspect) of the thumb, index and middle fingers, half of the ring finger and the palm area from the thumb to the middle of the ring finger. 

The median nerve also provides sensation to a part of the index, middle and half of the ring finger on the back of the hand. The median nerve is also responsible for the motor function of the forearm and the thumb. 

The median nerve block may be administered on the inside of the elbow, forearm or the wrist, but it is most often performed in the wrist, as the numbing effect may be more effective when administered via this approach.

Why is a median nerve block performed?

A median nerve block is performed to provide local anesthesia during surgical procedures involving the hand and fingers. The anesthetic blocks the transmission of pain signals to the brain.

A median nerve block may be performed solely or in combination with an ulnar and radial block:

  • To treat simultaneous injury to several fingers
  • For surgical repair of 
    • large abrasions or torn off tissue (avulsions),
    • fractures and dislocations,
    • complex lacerations,
    • nail infections and 
    • nail injuries
  • To lance and drain abscesses or cysts
  • During surgical procedures on the hand and fingers such as
    • Carpal tunnel release
    • Correction of Dupuytren’s contracture
    • Wrist keyhole surgery (arthroscopy, or laparoscopic joint surgery)
    • Finger joint replacement (arthroplasty)

Median nerve block is not performed in patients who have: 

  • Allergy to the local anesthetic
  • Anatomical distortion due to injury or from previous surgeries in the wrist
  • A surgical connection (fistula) between an artery and a vein for hemodialysis
  • Additional injuries in other parts of the arm that require a greater area of anesthesia
  • Infection or cellulitis in the injection site
  • Liver disease or failure

Benefits of median nerve block over other local anesthesia procedures include:

  • Immediate pain relief
  • Low requirement of anesthetic agent
  • Low risk of systemic toxicity

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How is a median nerve block performed?

A median nerve block is performed as an outpatient procedure and often in an emergency room. A hand surgeon usually performs a median nerve block for surgical procedures involving the hands.

The anesthetic agents commonly used for a median nerve block are lidocaine and bupivacaine depending on the length of time that anesthesia is required. The injection is administered between the two flexor tendons in the middle of the wrist.

Preparation

  • The patient lies flat with the hand appropriately positioned.
  • The doctor does a physical examination of the hand to assess its neurovascular function.
  • The injection site is sterilized with an antiseptic solution.

Procedure

The doctor

  • May use ultrasound guidance to position the needle.
  • Inserts the needle up to 2 cm into the skin at a perpendicular angle.
  • Aspirates the needle to ensure that it is not inside a blood vessel.
  • Injects 3-5 ml of the anesthetic solution.
  • Injects another tiny quantity of anesthetic in the tissues under the skin to form a small bump (wheal) while withdrawing the needle.
  • Massages the injection site gently to help the solution spread in the tissues.
  • Waits for up to 10 minutes for the nerve block to take effect.

Post-procedure

The doctor will instruct the patient on caring for the hand because anesthetized extremities are at a greater risk of injury, especially with long-lasting anesthetics.

How long does a median nerve block last?

The duration of the median nerve block’s effects depends on the kind and quantity of anesthetic agent used. 

Approximate duration of effects:

  • Lidocaine: Two to five hours
  • Bupivacaine: Five to 15 hours

The patient may experience tingling, discomfort or pain as the median nerve block wears off. Residual pain may be resolved with oral painkillers.

What are the risks and complications of a median nerve block?

Median nerve blocks are generally safe and effective for surgical procedures involving the hand. Potential complications include:

  • Infection at the injection site  
  • Pain at the injection site
  • Bleeding at the injection site
  • Hematoma
  • Nerve injury
  • Injury to blood vessel
  • Allergic reaction to the local anesthetic
  • Local anesthetic systemic toxicity
  • Unsuccessful nerve block

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Medically Reviewed on 5/29/2020
References
Medscape Medical Reference
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