Median Nerve Block

This page outlines the regional anaesthetic technique. For carpal tunnel syndrome see carpal tunnel injection.

Background

• Useful for lacerations across multiple fingers/palm instead of multiple digit blocks
• Useful for exploration of flexor tendons of digits 1-3
• Ultrasound guidance significantly increases the success rate of this block

The yellow area indicates the area of the hand innervated by the median nerve

Indications

• Trauma or need to perform painful procedure on area innervated by median nerve

Contraindications

• Infection overlying injection site
• Previous allergic reaction to local anaesthesic used
• Distortion of anatomic landmarks

Equipment Needed

• Topical anaesthesia (LET, EMLA)
• local anesthesia
  • Lidocaine 1% (lasts 30-60 minutes or longer if given with epinephrine, rapid onset)
  • Mepivacaine 3% (lasts 45-90 minutes, slower onset)
  • Bupivacaine 0.5% (lasts 2-4 hours, slowest in onset)
• 18G needle to draw up anaesthetic
• 25-30G needle to inject. Use of a larger gauge (21-23) makes it easier to see the needle on ultrasound
• 10 cc syringe
• Gauze pads
• ultrasound probe cover or tegaderm to cover probe surface

Procedure

Median nerve lies between palmaris longus and flexor carpi radialis.

• Time out, confirm correct patient and laterality
• Apply topical anesthesia if needed
• Draw up 5-10 mL of anesthetic into syringe
  • Beware of toxic dose of anaesthetic you're using.
• Before any nerve block, perform neurovascular exam (often includes 2 patient discrimination with paperclip)

Wrist Block

• Median nerve is within the carpal tunnel
• Between palmaris longus and flexor carpi radialis
• Insert needle perpendicular between tendons, 2-3 cm proximal to the distal crease of the wrist
• Aspirate; if no blood inject a few mL's of anaesthetic slowly
• Test sensation to pain distal to block

Elbow Block

Upper Extremity Nerves

• Cleanse the skin overlying the antecubital fossa with chosen antiseptic
• Create a sterile field using sterile drape
• In a sterile fashion, apply a small wheel of local anaesthetic to the area immediately proximal to the antecubital fossa
• Palpate the brachial artery to be aware of its path
  • The median nerve should be approximately 1 cm medial to the brachial artery at this point
• Insert the needle approximately 1-2 cm proximal to the flexor crease and advance with negative pressure applied to the syringe
• At 1-2 cm deep, aspirate prior to injection to rule out intravascular placement
• Inject 5-10 mL of local anaesthetic

Ultrasound Guided Block

Ultrasound-guided median nerve block

• Place a linear probe on the volar aspect of the mid-forearm
  • It may be easier to find the nerve by starting with the probe over the volar wrist and sliding proximally. The tendons will disappear as they become muscles but the nerve will remain as the only continuous round structure.
• The median nerve takes the appearance of a "chocolate chip cookie" in the axial orientation and lies between the flexor digitorum profundus and supeficialis
• Clean and prep the patient's arm under sterile conditions, and insert a 25 g needle in the long axis under ultrasound guidance next to the nerve
• Aspirate to prevent inadvertent intravascular injection
• Inject 5 mL of local anaesthetic so that it basks the nerve

Complications

• Bleeding
• Infection
• Pain
• Needle fracture
• Neurapraxia

External Links

• Emedicine: Median Wrist Block