resolution of superficial structures such as the femoral nerve. We recommend positioning the ultrasound screen on the opposite side of the patient bed from the side to be blocked (image 1). Expose the groin to identify the anterior superior iliac spine and inguinal crease. Prep widely with a sterilizing solution such as chlorhexidine, and place a sterile drape. The
Explore This IssueACEP News: Vol 30 – No 12 – December 2011
ultrasound probe should be cleaned in the standard manner and prepared with a sterile adhesive dressing across the probe contact surface (image 2).
Choice of Local Anesthetic
We recommend bupivacaine 0.25%-0.5%, or lidocaine 1%-2% drawn into a 20- to 30-mL syringe. All providers using nerve blocks should be familiar with the standard recommended dosages and clinical signs of toxicity, and have established protocols for treatment of local anesthetic toxicity that incorporate use of lipid infusions. For novice users, we recommend lidocaine rather than bupivacaine because of its higher safety profile in cases of inadvertent vascular injection. Using epinephrine-containing anesthetics can prolong the duration of the block and also provides an additional safety benefit: Sudden tachycardia, hypertension, and characteristic electrocardiographic T-wave morphology changes indicate accidental intravascular injection, alerting providers before large volumes of local anesthetics have been injected. A midcaliber needle such as 21 or 22 gauge provides adequate needle visualization without significant tissue trauma. Standard cutting needles can be used, and the length should be based on the depth of the nerve. We recommend a standard 20- or 22-gauge 3.5-inch spinal needle for most cases.
After ultrasound localization of the femoral nerve, raise a skin wheal with 3-5 mL of anesthetic at the anticipated point of needle entry. We suggest administering superficial anesthesia with a thin needle (25-30 gauge) after alcohol skin prep, prior to sterilizing the site and assembling the required material. This interval will allow for adequate local cutaneous anesthesia and reduce patient discomfort.
In the single-operator technique, the operator places the probe transversely across the femoral region of the upper thigh roughly parallel to the inguinal crease. The femoral vessels are then identified and centered on the screen. Gentle compression with the probe will collapse the femoral vein (medial) more easily than the artery (lateral). If desired, identification of the femoral vessels can be confirmed by using color Doppler imaging. With the femoral artery identified and centered on the screen, the operator should then follow the artery proximal to the inguinal ligament and distal to the takeoff of the profunda femoris artery. Proximal to this bifurcation, the femoral nerve will appear as a triangular or oval honeycomb structure 3-10 mm in diameter (image 3) covered anteriorly by the hyperechoic fascia iliaca.