Usage of the Nerve Stimulator – Other Limb Blocks and Intravenous Regional Anesthesia

by Brian Warriner, MD

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    00:06 So there are many Other Regional Blocks and virtually, every portion of a limb can be blocked using a regional technique. So, it's possible to do multiple blocks on the upper limb and multiple blocks on the lower limb. The way we used to do this, the way I was taught to do it, was to feel for an artery, the assumption being that the nerves to a certain area were closely in contact with that artery, pass the needle towards the artery until the patient complained of an electric shock going down their arm or down their leg. Obviously, not a pleasant experience.

    00:48 At which point we would inject. The problem was that it failed a lot of the time.

    00:54 And if you actually got too close to the nerve and pierced the nerve, causing that paresthesia, that electric shock feeling, you could actually damage the nerve. And because we weren't seeing where the needle tip was going, even though we were trying not to hit the artery that we were palpitating at the same time, it wasn't unusual to hit the artery and for hematoma to form in the area. So it really wasn't a very satisfactory technique. And many of us, essentially, stopped using regional blocks for upper limbs and lower limbs because of that problem. About 10 years ago, the use of the nerve stimulator to identify the nerve position was introduced.

    01:36 And this has actually made the whole technique more successful, but still not as perfect as I'm going to show in a moment. With a nerve stimulator you start with a low current, usually around 10 amps, mA and you advance it towards the nerve, and you watch the patient's muscles to see if there's a twitch that goes along with the nerve you're trying to block So what you'll see is this kind of thing. And, as you get close to the nerve, you turn down the current but you try to maintain the twitch, and you try to get as close to the nerve as you can, at the lowest possible current, around 1 mA is ideal, at which point you inject the local anesthetic.

    02:18 Again, the whole procedure is blind, other than the fact that you're putting a current in and you can see some movements in the limb. You can't actually see the position of the nerve. You can't see the position of any arteries that might be in the area. In the last 5 - 10 years, a technique developed by Vincent Chan in Toronto, has been widely accepted by anesthesiologists and this has really changed our mode of delivering regional anesthesia and has improved the outcomes dramatically. This is called ultrasound guided needle placement. And basically what it is, is using ultrasound to identify vessels and nerves, and then passing a needle through tissue, watching the needle with the ultrasound until you're very close to the nerve, and then injecting the local anesthetic at the nerve. And you can see all this using the ultrasound. But, as you'll see in the video we're going to show you, it's not as easy to see as you might think and it does require a significant amount of training and practice to become good at it. The good effect of this though has been that the success rate of regional analgesia and anesthesia has improved dramatically. And this has really improved care, particularly for patients having shoulder surgery, upper limb surgery, and lower limb surgery. A lot of the technique has led to excellent post-operative pain control, which we didn't previously have. Now we'll watch a video an ultrasound guided femoral nerve block. So this is an ultrasound guided femoral nerve block. And the large black object in the right upper corner, it's just disappearing now, is the femoral artery. And the way you know this is an artery is that, when the anesthetist compresses the tissue, the artery is not completely compressed. And this is a large artery, so you can actually see it pulsating. The anesthetist is now going to pass the needle from the skin, in a lateral fashion, down towards the artery. It's easy to see the shaft of the needle, but it's much more important to see the tip of the needle. And sometimes it's difficult to see the tip.

    04:36 That ultrasound opaque object that the needle tip is up against now is the femoral nerve. You do not want to enter that nerve. If you enter it, the patient will complain of severe pain or you'll notice when you try to inject local anesthetic that you can't. So back off from that if it occurs. But with ultrasound, once you learn how to identify the tip, you can go very, very close to the nerve. So you can see this tip, is right up against the nerve. And in just a moment we're going to actually be able to see the local anesthetic being injected there. You can see that little shadow that developed. And the local anesthetic surrounds the nerve or at least forms a pocket at the base of the nerve. And within a few seconds, the patient starts to lose sensation along the distribution of that nerve and the needle can be removed. Now, this portion here, the anesthetist is going anterior to the nerve, whereas the previous injection was posterior. They want to put a local anesthetic around the nerve, so they're going to inject anterior to the nerve as well. So regional anesthesia has improved dramatically with this technique that was introduced by Vincent Chan in Toronto.

    About the Lecture

    The lecture Usage of the Nerve Stimulator – Other Limb Blocks and Intravenous Regional Anesthesia by Brian Warriner, MD is from the course Anesthesia.

    Included Quiz Questions

    1. Localizing the nerve with the help of ultrasound guidance
    2. Localizing the nerve with the help of CT angiogram
    3. Localizing the nerve with the help of MRI
    4. Localizing the nerve by palpating the soft tissue
    5. Blindly injecting the anesthetic near the location of the nerve
    1. 1 mA
    2. 20 mA
    3. 3 mA
    4. 5 mA
    5. 15 mA
    1. Muscle twitch at < 0.5 mA
    2. Bleeding from an artery when the needle is inserted
    3. Current of 10 mA
    4. Locating an artery
    5. A tingling sensation in the limb
    1. Parasthesia
    2. Analgesia
    3. Anesthesia
    4. Allodynia
    5. Hyperalgesia

    Author of lecture Usage of the Nerve Stimulator – Other Limb Blocks and Intravenous Regional Anesthesia

     Brian Warriner, MD

    Brian Warriner, MD

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