Our last Capitol Ultrasound meeting was a huge success, with the Georgetown EM department graciously hosting the event in the simulation lab at Washington Hospital Center. As usual Michelle Saylor of Sonosite organized a great event, and with her colleague Don Rainville presented a fantastic hands-on session reviewing several commonly used ultrasound-guided nerve blocks. Below you’ll find a summary and photos of the 4 nerve blocks discussed: An interscalene approach to a brachial plexus block, a median nerve block, an ulnar nerve block, and a popliteal nerve block, as well as some additional resources for those interested in reading further about the subject. Join us at our next Capitol Ultrasound meeting for more exciting educational opportunities and great cases!
Interscalene approach to brachial plexus Block:
Transducer used: Liner, high frequency probe (13-6 MHz)
Region of anesthesia provided: Shoulder, upper arm, elbow
Indications: Shoulder and elbow dislocations, humerus fractures, large extremity lacerations
Technique: With patient lying supine or sitting, position the probe with marker towards patient’s left shoulder and in midline of neck.
Probe position for interscalene approach to brachial plexus block
Slide probe laterally until middle scalene muscle is visible, which appears as a small “fillet”:
Nerve bundles are seen in cross section between middle and anterior scalene muscles, and appear more hypoechoic than seen in other ultrasound images of nerves, which are typically brighter than surrounding structures.
Approach the nerve bundles with needle “in plane” with ultrasound beam, in longitudinal orientation. Typical amount of anesthesia injected varies by source but is often quoted in the range of 10-30 mL. Known complications of the procedure include intra-arterial injection with development of systemic toxicity, hematoma formation, neuropraxia, Horner’s syndrome from a large volume of anesthesia reaching the stellate ganglion , hoarse voice due to involvement of the recurrent laryngeal nerve, and ipsilateral diaphragmatic paralysis due to proximity of the phrenic nerve. Due to the possibility of these complications it is recommended that a larger volumes of anesthetic are avoided, that this block is avoided in those with chronic pulmonary pathology, and that bilateral inter-scalene blocks are never performed. Additionally, the more proximal the approach to the block, the higher likelihood of phrenic nerve involvement due to greater likelihood of C3-5 involvement.
Ulnar and Median nerve blocks:
Transducer used: Liner, high frequency probe (13-6 MHz)
Region of anesthesia provided: The Median nerve innervates the volar aspect of the palm and digits 2, 3, and half of 4, and the distal dorsal aspect of the same fingers. The ulnar nerve innervates the remaining half of the fourth digit and all of the fifth, as well as the hypothenar eminence .
Indications: large, avulsed finger and hand wounds, industrial injuries involving multiple digits
Technique: Using a high frequency transducer, both the median and ulnar nerves can be found above and below the elbow in cross section:
Probe position to find median nerve above elbow
Probe position to find ulnar nerve below elbow
Probe position to find median nerve below elbow
Probe position to find ulnar nerve above elbow
The median nerve appears as a hyperechoic bundle between the deep brachial vessels…
Median nerve lateral to deep brachial artery; probe position above elbow
The ulnar nerve appears as a hyperechoic bundle in cross section, scanned here above the elbow at the level of the triceps muscle
Red arrow points to ulnar nerve running through cubital fossa
Remember to thoroughly document a neurologic exam prior to performing any nerve block. Complications of these two blocks include hematoma formation, neuropraxia, and arterial puncture, but these blocks are fairly well-tolerated and low-risk.
Popliteal nerve block:
Transducer used: Liner, high frequency probe (13-6 MHz)
Region of anesthesia provided: The sciatic nerve becomes the popliteal nerve in the popliteal fossa, dividing into the tibial nerve posteriorly and the common peroneal nerve laterally as it traverses distally. The region of anesthesia provided is to the distal two thirds of the lower extremity, with the exception of the medial aspect of the leg. Cutaneous innervation of the medial leg below the knee is provided by the saphenous nerve:
With the patient supine, scan through the popliteal fossa in cross section:
Look for the popliteal nerve as the hyperechoic bundle of fibers lateral to the popliteal artery. Distribution of the anesthetic above the level of the bifurcation provides anesthesia to both the tibial and common peroneal divisions:
Red arrow points to thick bundle of popliteal nerve in fossa; lateral to popliteal artery
Complications include hematoma formation, neuropraxia, and arterial puncture, as described with the ulnar and median nerve blocks above. Additionally, a special consideration with the popliteal nerve block is the development of pressure necrosis of the heel in the setting of longer acting anesthetics such as Bupivicaine. Be aware that pressure ulcers can develop in less than 30 minutes, and care should be taken to elevate the lower extremity with stacked sheets or linens beneath the calf to remove pressure from the heel.
Additional resources from Mr. Rainville include a recommendation for the following text, “Ultrasound-Guided Regional Anesthesia and Pain Medicine”, by P. Bigeliesen, et al.
Also see an excellent collection of slides describing Ultrasound Guided Nerve Blocks by our own Dr. Liu of the GWU EM department. Hope to see you at our next meeting!
