Learn how to perform an ultrasound-guided transversus abdominis plane (TAP) block with this video from our Ultrasound-Guided Nerve Block Masterclass. You'll cover the distribution of this nerve block and how to use it to assist with procedures that involve the abdominal wall.
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[00:00:00] The anatomy behind the tap block or the transverse abdominis plane block can best be understood from a dermatomal perspective. Look at the above illustration. Note the zones innervated by roots T10 through L1. These are the nerve roots and the distribution that you can expect from a successful tap block. A good way to remember this
[00:00:30] is that the belly button, but 10, is covered by dermatome T10. As you see from this schematic, the nerves spread along the muscle layers and here, the fascia layers like finger-like projections. This is why this block relies more on a diffusion of anesthetic along this fascial plane and not simply an isolated nerve hydrodissection. Agent choice or anesthetic choice will be guided for how long you want the block to last.
[00:01:00] For instance, for a short ER or emergency department procedure lidocaine is sufficient. It lasts 1 to 3 hours and should be plenty for your procedure. For a longer duration block such as you would do in an operating room or postoperatively, choose ropivacaine or bupivacaine, as these agents last longer and will provide you with better anesthesia. This is also a bit different than most nerve blocks, in that you're hoping for diffusion of the agent along the fascial plane.
[00:01:30] That is why it is a higher volume block. Use 20 to 30 cc of your agent instead of 5 to 10 cc or mL. Your ultimate goal is to have local anesthetic spread between the transversus abdominis muscle and the internal oblique muscle. The most fervent experts at this block state that you can only use 20 cc and that would be sufficient. Needless to say, you need much more than you would typically
[00:02:00] need for an isolated nerve block. I will usually use 20 to 25 cc or mL of anesthetic. Here's a nice depiction of what nerve distribution you will receive from this plane block. Much like herpes zoster, this plane block follows a dermatomal pattern. Remember, this will only be a unilateral distribution. You are doing this on one side of the abdomen. You can only expect your anesthesia to spread it to about the level of the umbilicus
[00:02:30] on each side. Injection of local anesthetic, within the tap, can result in unilateral analgesia to the skin, muscles, and the parietal peritoneum of the anterior abdominal wall. Notice here how it only affects one side and not the other, depending on what side you perform your block. The exact caudal to cephalad spread of anesthesia depends on the block and it is variable. It's important that after
[00:03:00] you do this block to use a slight needle or a blunt tip object to check what level of dermatomal spread you achieved by your block. Here's the probe position you can expect to place on your patient. This is actually better viewed in real-time. Notice this is the right side of the abdomen. Your operator is holding the probe comfortably on the right flank. The umbilicus can be imagined to be approximately
[00:03:30] here, in the center of your screen. The corresponding ultrasound image obtained can be seen here. Immediately notice the fascial planes bright, white, and linear. Here's a muscle belly, here's a fascial plane, here's a muscle belly. Here, watch as the probe slides medially towards the umbilicus. You'll see as we now have three distinctive muscle bellies.
[00:04:00] Let's identify them. You see here one fascial plane muscle belly. Another fascial plane muscle belly. Lastly, this fascial plane. Keep your eyes focused on this fascial plane. You see here the last remaining muscle is your transversus abdominis muscle. This is also fascial in appearance. What do you think that might be? Think about the anterior abdomen and
[00:04:30] looking somewhat deep into it. You're right, this is the peritoneum. Below the peritoneum, you'll find intestines and critical structures that you absolutely want to avoid. Here we are zoomed in. Notice again the three muscles that we just identified, 1, 2, 3. External oblique, internal oblique, and then what we're looking for, the transversus
[00:05:00] abdominis muscle. The peritoneal space is just deep to that. Zoomed in a bit further, we see the three muscle bellies. You can imagine the peritoneal space is deep to this. Thankfully, we're looking at this fascial plane. We don't need to go further in that. The only spot that our needle needs to go is just beyond this fascial plane. If we get underneath this fascial plane, we can expect to have
[00:05:30] an adequate, successful tap block. I recommend doing this block in plane following your needle throughout its entire course. The reason for this is manifold. One, I always feel better when I can see the needle in the view, for the entirety of the procedure. And two, the peritoneum is very close by. You need to make sure you do not go deep enough to touch this peritoneum or God forbid pierce through the peritoneum into the critical structures we discussed momentarily. So, why would I perform
[00:06:00] a tap block? As I eluded to you before, this is a terrific block for abdominal surgeries. Surgeries such as hernia repairs that are located in the lower abdominal wall. Furthermore, there is great evidence coming out showing that it's effective for c-sections, especially postoperatively. Lastly, in the ambulatory setting, abdominal wall abscesses are prevalent. These are procedures that you want to do quickly and you would use a different
[00:06:30] anesthetic than you would if you were doing longer pain control such as surgical or postoperatively. So, with abdominal wall abscesses, I typically use lidocaine. This is a great indication for the tap block. Remember, go slow. The abdomen is sensitive much like the palms and the soles of our feet. The abdomen is full of nerve fibers. Go slow, be patient, and take your time.