Sunday, April 02, 2006


Opening day is tomorrow! Yippee! The ‘Stros won last night, 6-4, on a fabulous performance by Taylor Buckholz (7, 0, 5, 6, 0). I was a little worried he might succumb to nerves at Minute Maid (especially before a crowd of over 35,000) but he must have balls of brass. Anyone want to bet that Backe is sent down or waived by mid-May, and Buckholz moves up a spot (or two—the pressure’s on, Wandy!)?

Anyway, a while back I promised someone I would blog another post about an aspect of anesthesia. Actually, this is about a type of anesthesia—neuraxial anesthesia, i.e., spinal and epidural anesthesia. There are many applications for these techniques in anesthesia, not the least of which is labor and delivery. Spinal anesthesia is the technique of choice for cesarean delivery, providing the greatest margin of safety for both the mother and baby. Epidural anesthesia can also be used for cesarean, but is especially applicable to labor and vaginal delivery. Both techniques involve placing a needle into the back between the vertebrae, the idea of which is unpleasant for most people (doh!). The primary differences between the two techniques is the depth of needle placement, the types of medication used, and the fact that a small tube or catheter is left in place for epidural anesthesia. In this cross-section illustration, one can understand some differences. (The skin is to the right of the picture, so the needle will be penetrating the layers shown here from right to left.) With spinal anesthesia, simply put, a very small needle is placed between the bones, through the various layers, and through the dura mater (a tough fibrous covering over the spinal cord). The medication which is used is very concentrated and therefore a small volume, and because the needle goes through the dura, the medicine is placed more or less directly onto the spinal cord, although it is diluted by the cushioning fluid surrounding the spinal cord. With epidural anesthesia, a larger needle is used, and it is placed just short of the dura, into the epidural space (“epi” means “above” or “on top of,” so the needle goes above the dura). The needle has to be larger, because a tiny catheter is threaded through it into the epidural space, and left there while the needle is withdrawn. Because of the dura, the medicine pumped through the catheter doesn’t go directly onto the spinal cord, but instead bathes the nerve roots as they pierce the dura on their path to the body. A much higher volume of medicine is required, since it’s more indirectly applied. Also, since the catheter stays in place, the medicine can be continuously given over an extended period of time (such as labor), and more or less can be given to achieve the desired effect. (A spinal is a single-shot technique, no re-dosing without going through the entire process again.)

There are risks with both techniques, of course. With both techniques, your back will be sore for a day or two (just like your arm is sore after a vaccination). One of the risks with either technique is that it just might not work. Every person is different; the anatomy might just be slightly different, enough so that the anesthesia that results might be partial or ineffective. Another risk, since a needle is going into the back close to the spinal cord and/or nerve roots, is nerve damage. Another risk that bears mentioning is what is called a spinal headache. This is a very severe positional headache (only affects an upright person) that results from leakage of the cushioning fluid through the hole in the dura (also known as post-dural puncture headache). Because the needle used for spinal anesthesia is so small, the odds of a spinal headache after spinal anesthesia is actually quite small (counterintuitive, based on the names, huh?). The most likely time for a spinal headache is after epidural anesthesia, because sometimes the needle accidentally goes too deep (and the bigger needle makes a bigger hole, so more stuff leaks out). But not every person who experiences an inadvertent dural puncture will get a spinal headache. If a spinal headache occurs, it can usually be taken care with rehydration, caffeine, and if necessary, a procedure called a blood patch. (Blood from the patient is withdrawn from a vein and injected into the back where the hole is projected to be, which seals off the leak as it clots.)

All of these potential complications are very rare. The best way to help prevent them is to cooperate as much as possible with the person providing the anesthetic. While this sounds like a “duh” statement, it isn’t. The most important thing that a patient can do to facilitate placement of a spinal or epidural anesthetic is to be still. If you move while the needle is in your back, you greatly increase your odds of the needle going into a nerve or too deeply into your back. While this sounds like a simple thing, if your contractions are two minutes apart, it becomes a little more complicated. Also, the anesthesia provider will ask you to curl your back out toward them (think of a mad cat or a boiled shrimp). This position allows the bones in your back to spread out more, allowing better access to the space between them (think of an old-fashioned hand-held fan). Again, curling your back like that sounds simple—until you’re looking at trying to curl over a 40-week fetus. A little trickier.

Those are the most important points I wanted to mention. Considering that entire books have been written on these techniques, it’s obviously an incomplete discussion, but there it is.

I’m not sure how much I’ll be blogging in the weeks to come—I find it to be a fairly time-consuming pursuit, and I don’t really feel that I have much to offer, really, in coverage of the Astros or baseball in general. There are other great blogs out there that offer, if not the exact same "insights," then more consistent coverage, anyway, including live-blogging of games. I’ll keep up as best I can, as the team “inspires” me, but if nothing is here. . . um, sorry.


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