Epidural Anesthesia and Analgesia – Neuraxial Blocks

00:00 So, Epidural anesthesia. And this is a slide to give you some idea of the anatomy of the Spinal cord. And you will see as you look at the slide, on the lower portion of the slide is the Dorsal Spinous Process of the Vertebra. And just in turn, interior to that, going towards the large white object at the back, which is The Body of the Vertebra, you pass through a number of Ligaments and The Spinal Column itself.

00:32 Before you get to the spinal column, there's a thick ligament called the Ligamentum flavum.

00:38 And it is the space between the ligamentum flavum and the coverings of the spinal cord that is the Epidural Space. That's where we put Epidural Catheters, that's where we inject for Epidural Analgesia or Anesthesia. If we just pass the needle a tiny bit further, 2 or 3 millimeters at most, we actually enter the spinal cord space and that's what we do when we're doing Spinal Anesthetics.

01:08 So the catheter is inserted between the ligamentum flavum and the Dura of the spinal cord, which is really kind of a potential space, it's filled with fat and blood vessels. We can actually transport a catheter into that space and we inject local anesthetics usually quite dilute into the space, and that can produce good analgesia to the lower half of the body. The concentration of the local anesthetic determines the depth of the block, in other words the intensity of the block. And it can be adjusted to allow the patient to walk with the epidural in place or, if we need to take the patient to the operating room and operate, we can actually deepen the intensity of the block, increase the intensity of the block to do surgery. And this commonly happens in women who are in labor. We use very dilute solutions to prevent pain during labor. And then, if we do need to take them to the operating room and do a Cesarean section, we increase the intensity of the block, so they'll tolerate the actual surgical procedure. So the easiest way to put in an epidural is with the patient in the sitting position because it straightens the spine. And I'm going to refer to the patient as a woman because, in most cases, more commonly we use it in women than in men, simply because it's widely used in Obstetrical Anesthesia. We draw a line between the superior spines of the pelvis, and in theory that line goes through the dorsal spine, the dorsal spine as process of the Lumbar 4 vertebra. In fact, recent studies have shown that it varies anywhere up to one to two vertebra from that position.

03:02 But we usually still do this technique just to get a sense of where we're going and to feel the landmarks in the back. And the landmarks we're feeling for, are the dorsal spines of the lumbar vertebra and the spaces between the lumbar vertebra. You don't have to have the patient sitting to put in an epidural. And frequently, women in labor find it more comfortable to be on their side when the epidural is placed. So, one has to learn how to place the epidural with the patient in the lateral position, either left or right lateral, which means you have to learn how to kind of go backwards in some situations. Particularly if they're lying in the right lateral position facing away from you.

03:44 But amazingly it's quite possible to learn how to do this. It's unusual to put the patient's head up or down, but sometimes patients will request this, and it certainly is possible to put in an epidural with the patient in those positions. So this is the needle insertion for the lumbar space. And this is the kind of epidural we place for labor and for lower abdominal or a limb surgery. If you look very carefully at the diagram of the vertebra, you'll see that the dorsal spine, that portion of the vertebra that sticks out towards the back, is very short and straight in the lumbar region. So the needle is usually placed just under the dorsal spine, above the subsequent dorsal spine in the space and slid in through the ligaments towards the epidural space. The Thoracic insertion is quite different. And we use thoracic epidurals for management of pain postoperatively after thoracic surgery, and after upper abdominal surgery. You can see that the thoracic vertebra, the dorsal spine doesn't come straight out, it actually points inferiorly, it points towards the bottom. And to come in on the midline in this situation is quite difficult. You have to come in at an angle that's very steep, and it feels very unnatural when you're doing that. So most of us actually step away from the vertebra to approximately 1.5 - 2 centimeters lateral to the vertebra and come in on an angle from the side, but not near as steep an angle, much, much shallower angle and it's much easier to do that way.