Some cases require ultrasound-guided femoral nerve anesthesia. Complex fractures of the pediatric femur are excruciatingly painful and the wait prior to surgery can be agonizing for everyone involved.
Your hospital system recently opened a freestanding ED in a growing area outside the city. You left home early this morning as you were uncertain regarding the driving conditions following the winter’s first storm that has caused numerous school cancellations.
A few minutes prior to your arrival, an 8-year-old girl arrived via EMS following an accident that occurred while she was sledding with her parents and brother. The outgoing physician on duty—both surprised and delighted that you are early—comments that the patient is experiencing considerable pain in response to an obvious femur fracture (Figure 1 above). She was transported to your facility instead of the main hospital in response to her parents’ request as her considerable fracture pain had not been controlled by protocol doses of morphine. Subsequent to your colleague administering an additional dose of morphine, the patient began vomiting and became hypoxic, necessitating the provision of a small amount of supplemental oxygen.
Your competent and conscientious colleague reports that primary and secondary surveys are otherwise unremarkable but adds that she is uncomfortable providing additional narcotic doses in view of the potential for worsening respiratory depression.
Fortunately, both you and your colleague recently attended a workshop on the provision of ultrasound-guided regional anesthesia. Although not the way either of you envisioned your first case, you both believe you can and should perform a femoral nerve block to attenuate your patient’s pain. You believe this will facilitate what may otherwise be a prolonged and difficult transport to the main hospital trauma center where operative stabilization can occur. Fortunately, one of the facility’s nurses has experience with regional anesthesia and procedural sedation. The parents report no allergies and are very eager for you to intervene on behalf of their daughter.
Because travel to the main hospital could take several hours, you decide on the use of a longer-acting local anesthetic that was recommended during your workshop: Ropivicaine. The accepting orthopedic surgeon at main hospital has reviewed the PACS images, requests that you attempt to reduce the friction, and suggests you can proceed with a femoral nerve block if comfortable.
While your colleague discusses the potential benefits and risks of regional anesthesia with the parents, you prepare for the recommended two-person procedure utilizing a block needle attached to a 20 cc syringe via extension tubing. You will use ultrasound to guide the block needle to the target nerve, while your colleague will handle the syringe containing the ropivicaine.
You visualize the femoral triangle in transverse plane and appreciate the usual lateral-to-medial nerve-artery-vein progression (Figure 2 below). You estimate your needle trajectory in the long axis and inject a small amount of lidocaine anesthetic in the skin at your projected needle entry point.
Figure 2. Transverse ultrasound image of the femoral triangle [lateral]
Holding a high-frequency linear probe in one hand and the block needle in the other hand, you proceed from lateral to medial and begin to see the needle shaft in the soft tissue lateral to the probe. Proceeding further, you direct the needle toward the posterior (deep) aspect of the femoral nerve, which has a characteristic stellate shape and honeycomb appearance.
Unfortunately, as you proceed, you see the needle shaft but can not identify the needle tip. Your colleague reminds you that visualizing the needle tip is essential and that the appropriate descriptive terminology suggests you are “partial plane” relative to the probe. She encourages you that seeing some of the needle shaft means you are close to full in-plane visualization.
Stepping back a bit, you look at your needle and probe and attempt to realign them while your knowing colleague observes the screen. Fortunately, with only a small reorientation of the probe, you and she identify the full extent of the block needle including the needle tip, which is only slightly lateral to the posterior aspect of the femoral nerve. Proceeding slightly further, you see the needle tip approximating the epineurium. You ask your colleague to pull back on the plunger of the attached 20 ml syringe. No blood is aspirated, providing a degree of reassurance that the needle tip is not within a blood vessel. Your colleague slowly administers six milliliters of ropivicaine and you both observe as the femoral nerve becomes more visible in contrast to the hypoechoic appearance of injected local anesthetic.
Emboldened by your success, you withdraw and redirect as you now approach the anterior aspect of the target nerve at about 12 o’clock. Your colleague again attempts aspiration (negative) prior to slow instillation of another six mls. The infusing hypoechoic ropivicaine is clearly visible as it contrasts with the more echogenic target nerve (Figure 3 below). Convinced that you have fully surrounded the nerve, you look at your colleague who signals affirmation, and subsequently remove the needle. Only then do you remember to ask your nurse to observe the cardiac monitor for signs of QRS widening, heart block or arrhythmia. Fortunately you colleague had directed her to do this while you were setting up the equipment.
Figure 3: Femoral Nerve Block [lateral]. The block needle is anterior to the nerve with surrounding hypoechoic local anesthetic.
In approximately 15 minutes, your patient comments on how her leg feels much better. You subsequently apply a Hare traction splint to effect elongation of the fractured femur, after which fracture alignment appears much improved. Although the ambulance ride to the main hospital requires almost two hours due to the inclement weather and road conditions, it is very well-tolerated by the child who undergoes surgical stabilization later in the afternoon.
Pearls & Pitfalls in Ultrasound-Guided Femoral Nerve Anesthesia
- Ultrasound Guided Regional Anesthesia is a profoundly benevolent application of bedside ultrasound. Parents of children experiencing successful femoral nerve blockade in our emergency department have expressed immense appreciation for the customary six to eight hours of pain relief provided their children; often sufficient to make for a restful night prior to operative reduction the following morning.
- Preparation is important. Pre-procedural sonographic visualization of the neurovascular bundle contained below the fascia iliaca facilitates subsequent accurate deposition of local anesthetic (Figure 4 below). Most children benefit from pre-procedure local anesthetic at the site of planned block needle insertion.
- Characteristics of the local anesthetic should be considered in the clinical context. Nerve blockade intended to enable brief procedures may utilize shorter-acting anesthetics such as lidocaine, while medications such as bupiviciane and ropivicaine provide much greater duration of action. Communication with orthopedic colleagues is essential, particularly at the inception of a nerve-block program.
- Ropivicaine is a long-acting amide local anesthetic agent that is well tolerated in children. It is structurally related to bupivacaine, but is a pure S(-) enantiomer. Ropivicaine has reduced lipid solubility and — in combination with its stereo-selective properties — is less likely to cause cardio- and neurotoxicity. A recommended dose for femoral nerve anesthesia is 0.5 to 1 ml/kg of the 0.5% solution; equal to 2.5 to 5 mg/kg body weight. Our upper limit for dose volume in adult-sized pediatric patients is 40 milliliters of the 0.5% solution.
- Attention to ergonomics is very helpful. We prefer a two-person technique using a block needle attached to a 20 to 40 ml syringe via intravenous tubing (Figure 5 below). This allows the sonographer-emergency physician to maintain focus on the ultrasound screen and achieve co-linearity between the transducer and the full extent of the block needle shaft and needle tip. Positioning the ultrasound monitor in alignment with the needle path facilitates continuity of sonographer visual focus.
- Optimal technique utilizes transverse axis visualization of the femoral nerve with in-plane observation of the block needle as it proceeds in a lateral to medial direction. (Figure 3). Flush the tubing and block needle immediately prior to the procedure. Begin by aiming the local anesthetic deep/posterior to the target femoral nerve. The initial flush—as well as deposition of the initial administration of local anesthetic as posterior as possible—diminishes the possibility of an inadvertent air bubble obscuring relevant anatomy or the block needle. Instill the local anesthetic posterior and anterior to the target nerve; aspirating prior to instillation for additional reassurance that the needle tip is not within a vessel. The local anesthetic will appear hypoechoic as it surrounds and highlights the target nerve.
- Over-zealous administration of the local anesthetic within the nerve is not necessary and may cause nerve damage. Deposition of local anesthetic adjacent to the epineurium is adequate for satisfactory anesthesia.
Figure 4: Femoral Nerve Block. The arrowheads designate the block needle. Image courtesy of Beth Spurlin, MD, Ph.D, University of Louisville Pediatric Emergency Medicine.
Figure 5: Two Operator Nerve Block Procedure