Femoral nerve block


  • FNB (3 in 1) block should be performed under ultrasound guidance [BestBets]
  • Used for #NOF, shaft of femur or fractures of the patella
  • Obtain IV access before performing this technique (risk of LA toxicity)


  • Something to clean the skin
  • 1% lignocaine in one syringe, with a 25G needle for skin infiltration
  • 0.5% Bupivacaine in another syringe(22G anaesthetic needle for the nerve block)

LA toxicity

  • The toxic dose for Lignocaine is 3 mgs per kilo or 20 mls of 1% Lignocaine for an adult
  • In a child = 1 ml of 1% plain Lignocaine for each year of the child's age
  • Before any regional anaesthesia ensure you are familiar with the signs / management of LA Toxicty


Photo femoral nerve block
  • Very gently, slightly abduct the femur on the affected side
  • Identify the femoral artery and keep one finger on it
  • The nerve lies lateral and deep to the artery (see diagram)
  • Clean the skin
  • Infiltrate the skin with lignocaine
  • Infiltrate around the nerve in a fan-like fashion with Bupivacaine
  • Aspirate frequently to avoid intravascular injection
  • If you puncture the femoral artery compress it for 5-10 minutes
  • If the bleeding stops continue with the block
  • Wait 10-20 minutes before manipulating the limb into a splint
  • Monitor the patient for local anaesthetic toxicity

Max dose of local anaesthetic Bupivacaine 2 mg/kg ( = 0.4 ml/kg of 0.5% bupivacaine )

You can use a mixture of lignocaine and Bupivacaine.  If mixture used then maximum dose should be 2mg/kg in total.


The RCEM have issued an alert re death after a fascia iliaca block. Please ensure you:

  • Site, side, dose and time of block
  • Frequency of post procedure observations. A minimum would be at 5, 10, 15, 30 mins post procedure

FNB in anticoagulated patients

  1. Femoral block technique probably safe [ESRA/ASRA statement 2018] especially when balancing risk/benefit for elderly patients with NOF
  2. Use small regional anaesthesia needles (22G) and ultrasound guidance
  3. Target the nerve rather than the iliacus plane/muscle
  4. Avoid vessel puncture (doh!)

Content by Dr Íomhar O' Sullivan. Last review Dr ÍOS 23/10/21.