By Peter Croft, MD - 4th Jun 2018 - Course previews

Distinguishing nerves with ultrasound.

The first step to a success nerve block is to distinguish the nerves you need to anesthetize. Ultrasound makes this process much easier. Learn how to easily recognise soft tissue structures with ultrasound and distinguish nerves from surrounding structures.

 

Join our Ultrasound-Guided Nerve Block Masterclass

Master the use of ultrasound to guide your nerve block procedures with our Ultrasound-Guided Nerve Block Masterclass. You'll learn how to identify and anesthetize nerves in the neck, torso, and lower extremities with the help of ultrasound, and build an appropriate nerve block protocol within your hospital. 

 

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Video Transcript

[00:00:00] Before we dive deep into nerve blocks, it is critical that we amass a fundamental understanding of differentiating anatomical structures, with ultrasound. That is how certain structures such as bone, tendon, muscles, and nerves appear with ultrasound and how to distinguish them from one another. First and foremost—nerves, that is, of course, the topic of the course. Nerves appear honeycomb-like. The 

[00:00:30] fascicles inside them take on this honeycomb appearance. As you can see here in your screen, in the middle of your screen, a nerve bundle. Notice the small little fascicles within its core. Also, notice how bright it is compared to the surrounding tissue over here, over here, up here. This is called hyperechoic. It has echoes within it. Echo meaning white. When learning ultrasound 

[00:01:00] of any application or indication, whether its nerves or heart or lungs, the tendency is to be hesitant and deliberate with the movement of your probe. I advocate for just the opposite. Don't be bashful, move that probe briskly and watch as the structures underneath dynamically change. Tendons become muscles, nerves stay static in caliber, in size, vessels will compress if you put pressure on them, they will dive deeper 

[00:01:30] and more shallow. No better example of this can be seen than in the carpal tunnel. Here, recognize the circular structure superficially. Without moving the probe, it is unclear which of these circular objects is the tendon and which of them is a nerve. They are not black or anechoic, lacking of echoes. So, they are much less likely a vessel. Also, note the 

[00:02:00] hyperechoic or bright white line, just below these circular objects. The bright white line means that the ultrasound waves that are coming from your probe are being blocked. By definition, something that blocks ultrasound waves must be quite dense. In this case, notice the shadow and beyond the hyperechoic rim. This shadowing tells you that this is most 

[00:02:30] likely a bone or in this instance, in a carpal tunnel, the carpal bones. Here, watch as we slide that probe briskly up towards the elbow. Notice here how our tendons are becoming muscles. They are changing in size, changing in caliber. See if you can notice the one thing on the screen that stays static. 

[00:03:00] This is your median nerve. Notice it here. Watch it from the beginning. See if you can identify which circular object is the nerve at the outset. Perfect. Here's a still image of the median nerve in the proximal forearm. Notice that honeycomb-like appearance and that hyperechogenicity, bright white. 

[00:03:30] Notice the muscle tissues surrounding it as well as the hyperechoic fascial lines here. Notice the difference between hyperechoic fascia and that hyperechoic bone we saw. Remember the bone shadows, the fascia is not dense enough to block all the waves so some of the waves as you can see pass through. Lastly, I want you to draw your attention to the top left of your screen at the circular anechoic 

[00:04:00] object. Without putting pressure on the probe, I can't tell whether this is vein or artery, however, I know it is one or the other. So, to lead into distinguishing vascular structures, we need to use compression. Nerves cannot be compressed without any amount of force. Vessels, on the other hand, can be. Watch as I push down on the skin and the vein compresses. 

[00:04:30] Tubular anechoic vascular structure, easily compressed. This is a vein. In this image, you'll see examples of nerve, artery, and vein altogether. This association will become a theme in this course, nerves running with vessels. Neurovascular bundles are extremely common in the body. In the arms, in the chest, in the belly, and in the legs. At the top of 

[00:05:00] your screen, notice that circular hyperechoic honeycomb-like nerve. Just to the left and inferior to it, will be your vein. At this point, we can't tell the difference, right? We're not actively compressing it. We're not watching Doppler flow to see pulsatile nature. And then just below that is your artery. Watch as we confirm, who we suspect to be true, in the video. See, there 

[00:05:30] is the vein, easily compresses and the artery does not. You can also see that moving the probe just slightly gives you a better idea of this static circular hyperechoic nerve. This is the popliteal fossa. We will explore this in a later chapter. So to review, anechoic circular structures, whether they're 

[00:06:00] compressed or not compressed are either vein or artery. Echogenic structures, look for a shadow. If you see a shadow, that tells you it is likely bone. If there is no shadow, then that can be either muscle tissue, tendon tissue or nerve tissue. If we look at each of these individually, we want to notice how organized they are. Remember that muscle is not 

[00:06:30] as circular and organized as the other tissues. Remember, it changes. Recall the clip of the forearm, as we swept up towards the elbow and the tendons become nerves and became wider. Nerves, on the other hand, will be circular and organized, as will tendons, if you stay in place. So, that brings us into differentiating tendons and nerves. By simply moving your probe along the skin, you can see if 

[00:07:00] the nerves or tendons change. Static objects will be your nerves. Changing dynamic structures into muscles will confirm that you are looking at tendon. So, by being active with your probe, not being afraid to move around, especially at the beginning of your learning, you will start to see tissue differently. And by doing so, you will become very comfortable distinguishing nerves from their surrounding structures.