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Welcome to our residency blog.

US Guided Femoral Nerve Block

US Guided Femoral Nerve Block

Case

76 year old F with a history of DM2, hypertension, dementia, COPD and osteoporosis presents to your emergency department after a ground level fall. The patient reports she was walking her dog and her dog chased after their neighbors cat. The patient was pulled to the ground and fell onto her right side. She thinks she may have landed on a small wall made of bricks. She noticed immediate pain in her right hip and lower back and was unable to ambulate on scene. Vital signs are within normal limits. Exam demonstrates ecchymosis over the right greater trochanter with active ROM of the right leg limited by pain in the hip. Sensation is intact and DP pulses are symmetric in the lower extremities. The remainder of your exam is normal. X-rays of the right hip and pelvis demonstrate a mildly displaced fracture through the proximal neck of the right femur. 

Background

Hip fractures are a common injury in the emergency department and are directly related to significant morbidity among the elderly patient population. Pain control can be difficult as this patient population is at an increased risk of delirium and drug interactions. Ultrasound-guided femoral nerve and fascia iliaca nerve blocks have been demonstrated to be safe and effective in managing pain related to hip fractures [Ritcey et al]. Nerve blocks help limit the overall amount of narcotic pain medication required in these patients.

While nerve blocks have been shown to be safe, patient selection should be done in consultation with surgical teams who will definitively manage the fracture. Compartment syndrome is a theoretical risk and should be considered prior to the procedure.

 
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Block Dermatome

The femoral nerve and fascia iliaca blocks have great coverage of the entire femur and proximal tibia. It also provides cutaneous anesthesia of most of the anterior thigh and medial leg to the foot. You can see why it’s a great option for femur fractures!


Equipment

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Take the time to gather everything you need before you start the procedure. No need to over think things, a checklist offloads the cognitive part so you can focus on the procedure. Here’s one to get you started, modify it based on your own practice and equipment availability.

 

Setup

Set up the ultrasound on the opposite side of the bed from you so you can look directly over your hands while doing the procedure. Scout your window using the linear probe, start at the inguinal crease. You’ll find the femoral nerve just proximal to the bifurcation of the femoral artery giving off the femoral artery profunda. Once you feel like you have the window you like, use the end of a syringe to make a skin impression to mark your spot.

Finally, using doppler, scan through the likely trajectory of your needle to look for any vessels that could be in your path.


In-plane view of the FNB/FIB. The needle (green) is traversing the fascia iliaca (purple). The femoral nerve (yellow) is a triangular structure just lateral to the femoral artery (red).

In-plane view of the FNB/FIB. The needle (green) is traversing the fascia iliaca (purple). The femoral nerve (yellow) is a triangular structure just lateral to the femoral artery (red).


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Local Anesthetic

You should get in the habit of calculating the max volume (via max dose in mg) every time you do a procedure. It won’t matter as much when you’re sewing up small lacs but with blocks, it’s essential! So practice when the stakes are lower so you’re ready when it matters.

Maximum allowable dose (mg/kg) x (weight in kg/10) x (1/concentration of local anesthetic) = mL anesthetic

When you draw up your anesthetic, think volume instead of concentration for best effect. It’s better to inject a larger volume of lower concentration anesthetic than a smaller volume of higher concentration. Once you calculate your max volume anesthetic, you can dilute that down to achieve higher volume.

Also, when you draw up the anesthetic into the syringe, leave 10-20mL of air in the syringe. This will act as a “pressure gauge” when you’re injecting. If the air column compresses more than 50% while injecting, the resistance is too high and you’re likely not in the right spot.

 

One LAST thing…

Local anesthetic toxicity can be life-threatening. Most reported cases have been from single injections. When doing blocks, know where intralipid exists in your department or hospital. Many places have “block carts” that are stocked with intralipid. Always have IV access when doing blocks and keep patients on monitors. Neurologic effects will often precede cardiovascular effects, though not necessarily true for bupivicaine. The dose for intralipid is 100mL bolus (1.5ml/kg lean body weight technically) and can be repeated 1-2x q3min for asystole. Otherwise follow with infusion: 0.25-0.5ml/kg/min for 60 minutes. You can consider using and 18g to draw intralipid from the bag into 30 or 60cc syringes to push rapidly.

Leave some air in the syringe for real-time resistance feedback.

Leave some air in the syringe for real-time resistance feedback.


Procedure

Alright, you got consent, marked your spot, gathered your equipment and prepped the patient.

For the block, you’ll be using a 20g, 3.5in Quincke needle in most cases. This is just the spinal needle used for LPs. Take the obturator out of the barrel of the needle and set it aside. Make a skin wheal with anesthetic.

When you’re first learning this procedure, a two person technique is sometimes easier. One person driving the ultrasound probe and the needle, the other injecting anesthetic. Either way, set up the ultrasound machine directly across the bed so you, your hands, the syringe, probe and ultrasound machine are in a straight line. This will maximize your success with the in-plane approach, which is the preferred approach as it allows for visualization of your needle tip at all times.

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This can be difficult and takes a lot of practice to develop the dexterity to do efficiently. One way to practice is to buy a couple packs of tofu and put uncooked spaghetti noodles under the tofu in the package. The noodles will look just like a nerve on ultrasound. Practice with a Quincke until you feel comfortable making micro-adjustments in real time to keep your needle tip in view!

Keep in mind that a steeper needle angle makes tracking the needle on ultrasound more difficult. If the structure is > 3cm deep to the skin, consider entering the skin 1-2cm from the probe to allow for a shallower needle angle. Enter the skin perpendicular to the skin, then drop your angle down appropriately. This makes it easier for the Quincke needle to enter the skin and limits the amount of skin and subcutaneous tissue sliding over muscle as you advance the needle.

Once you’re through the skin, stop advancing the needle and find the needle tip! Remember, everything needs to be directly in line to pick up the needle on ultrasound. Once you have the needle in view, advance the needle toward your target. Use tiny movements and always keep the needle in view. If your needle tip is out of view, you have to assume it’s in a vessel or nerve. Keep advancing in mm increments and think to yourself “advance the probe, advance the needle.” If you advance the needle before the probe, you’ll be advancing the needle blindly.

Once you feel you’re in the right spot, you can inject a small amount of anesthetic to hydrodissect the tissue planes. The femoral nerve should look like it’s being peeled away from the surrounding connective tissue. Another option when you’re first starting is to use saline to hydrodissect to save your anesthetic. When you can confidently observe the anesthetic in the optimal spot, inject in 5-10mL increments, then stop and aspirate to make sure your needle hasn’t gone into a vessel. Also keep an eye on tissue resistance and the “pressure gauge” you created in the syringe. If you’re getting resistance, withdraw half a mm and aspirate, inject a small amount and reassess the resistance. Once you’ve injected your full anesthetic amount, flush the line with a few mL of saline.

Monitoring

Give the patient specifics signs and symptoms of LAST to watch out for. Tell them to push the call button if they feel perioral numbness/tingling, palpitations, tinnitus etc. Keep them on monitors to watch for arrhythmias and other cardiovascular changes.

Pearls & Pitfalls

  • Femoral nerve blocks are safe, effective and opioid sparing

  • Set up the room and your equipment exactly how you want it

  • The U/S machine, your probe, the needle, your hands and chair all need to be perfectly aligned to maximize success

  • Calculate max anesthetic volume

  • Always keep your needle tip in view

  • “Advance the probe, advance the needle”

  • Know where to find intralipid and how to give it

  • Educate the patient on signs and symptoms of LAST

  • Practice micro-skills of in-plane U/S-guided procedures with tofu and spaghetti noodles


References

Ritcey, B., Pageau, P., Woo, M., & Perry, J. (2016). Regional Nerve Blocks For Hip and Femoral Neck Fractures in the Emergency Department: A Systematic Review. CJEM, 18(1), 37-47. doi:10.1017/cem.2015.75

NYSORA - Ultrasound-guided Femoral Nerve Block

ACEP Now - Ultrasound-guided Femoral Nerve Block

EM:RAP - Fascia Iliaca Compartment Block (Video)

Highland EM - Ultrasound-guided Femoral Nerve Block


A huge thank you to Dr. Alex Miller (alum 2019) for his contributions to this post and for promoting regional anesthesia among our residents.


Signed: Jordan Wackett, MD, MPH

Co-Signed: Jane Xiao, MD, MSE - OHSU Ultrasound Fellow




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