We suggest a lateral to medial in-plane approach. After the femoral nerve and overlying fascia iliaca are identified, enter the skin with the needle bevel up about 1 cm lateral to the probe. The angle of entry will depend on the target depth of the fascia iliaca. More shallow angles of entry will improve needle visibility.
Explore This IssueACEP News: Vol 30 – No 12 – December 2011
Advance the needle slowly, maintaining the shaft and tip in view at all times. Target the hyperechoic fascia iliaca overlying the iliopsoas muscle 1-3 cm lateral to the femoral nerve. Once beneath the fascia iliaca, aspirate to confirm the needle tip has not entered a vessel and then slowly inject 3-5 mL of local anesthetic. With the needle tip in view, the spread of hypoechoic injectate should be visualized in real time with superficial movement of the fascia iliaca toward the skin surface (image 4). After confirming optimal needle tip location, proceed to inject a total of 10-20 mL of local anesthetic in 3- to 5-mL aliquots. If at any point the spread of local anesthetic is not visualized, intravascular injection should be suspected and the procedure halted. After injection, examine the patient for any signs of anesthetic toxicity such as perioral numbness, dizziness, or convulsions.
Remaining at least 1 cm lateral to the femoral nerve and vessels reduces the risk of vascular puncture or intraneural injection. When larger volumes (20-40 mL) of local anesthetic are used, there is typically sufficient fascial spread of the local anesthetic to block the lateral femoral cutanteous nerve, resulting in a “fascia iliaca block.” Retrograde spread of local anesthetic sufficient to block the obturator nerve in a so-called “3-in-1 block” is highly unpredictable, and additional maneuvers such as distal compression and Trendelenberg positioning have questionable efficacy.
Evaluating Block Efficacy
Successful blocks are associated with direct visualization of hypoechoic local anesthetic displacing the femoral nerve anteriorly, and subsequent tracking of anesthetic distally resulting in a donut-like pattern circumferentially surrounding the nerve. Depending upon the local anesthetic used, block onset should occur within 15-25 minutes and last 3-8 hours.
Ultrasound-guided femoral nerve block is an ideal procedure for the emergency physician to incorporate into clinical practice. Controlling pain from hip, midshaft femur, and patella fractures is often difficult, and classically taught techniques (progressively increasing doses of intravenous opioids) can lead to respiratory depression and changes in sensorium. Ultrasound-guided femoral nerve blocks enable targeted deposition of anesthetic and are a crucial part of a multimodal approach to pain management for the acutely injured patient.