Background:
In obstetrics an epidural is usually placed for labor and delivery. It is placed for pain control. Typically the epidural is placed during active labor, however an epidural can be placed prior to active labor if the patient is committed to labor. In some cases an epidural may be placed not for labor and delivery but for use during a cesarean section (c/s). The reason is that an epidural can be used for a prolonged c/s.
An epidural differs from a spinal due to the anatomic placement and the resultant effects. An epidural needs a larger volume of local anesthetic to be as effective as a spinal anesthetic. An epidural is typically administered via a catheter which allows the anesthesiologist to titrate the anesthetic slowly, which isn't the case typically in a spinal anesthetic, and also allows for a continuous infusion of local anesthetics which is comforting during a labor.
The diagram above will serve to conceptualize the anatomy of the epidural procedure. To the left on the illustration is the skin. To place an epidural a needle transverses the skin, next the interspinous ligament (between the spinous processes which are the knobby projections in the middle of your back), then the ligamentum flavum, and finally the epidural space. We do not want to enter the dura, because for an epidural we are using a much larger needle than what we typically use for a spinal procedure, so that means if you puncture the dura with an epidural needle the chances of a spinal headache after the procedure are very high.
The Procedure:
Above is a typical epidural kit. When you request an epidural you obstetrician will page for the anesthesiologist or nurse anesthetist. The anesthesiologist will interview you and do a history and physical. Basically we are ensuring you are an appropriate candidate to receive an epidural. Our main concerns are to rule out an bleeding abnormalities, neurological or cardiac issues. We also want to make sure the delivery is running smoothly, although the obstetrician will alert us prior to us seeing you if there are any issues. We will look to see if there is any pertinent blood work drawn and we will also ask about the pregnancy. Verifying that there are no issues during your pregnancy or with past pregnancies or with past epidurals. The main risks associated with epidural placement are causing a post epidural by inadvertently going through the dura as described above. We also inspect the back to ensure no skin infections in the area that we will be placing the epidural. We typically place the epidural in the lumbar area. Typically below the L2 area, although this isn't as stringent as with a spinal since we will not be going intrathecally (below the dura, and potentially injuring the spinal cord). Risks of dosing the epidurally are typically hypotension, or lowering of the blood pressure and causing fetal decelerations. I dose my epidurals slowly and make sure that my patients have received adequate fluid boluses. This has been highly effective for me. Other less common risks include seizure, paralysis, and death. These risks are a lot less common.
After we obtain consent, we prepare to place the epidural. We sterilize your back with a prep solution. After doing this we wash our hands and don sterile gloves and draw up the local anesthetic. I find the spot that I will be placing the epidural and put local anesthetic in that area.
I allow the local time to take effect. In the picture above is a blue hubbed needle, this is the needle I use to infiltrate the skin with local anesthetic. Next I use the needle that is in the picture that has the silver and black demarcation. This is what is termed a Tuohy needle. This is the needle that will be used to place the epidural catheter. I slowly advance the Tuohy needle through the skin, the interspinous ligament, the ligamentum flavum (there is a characteristic popping sensation).
Once I am in the interspinous ligament area, I pull the plastic stylet that is in the middle of the Tuohy needle and place the syringe in the picture above onto the back of my Tuohy needle. This is my loss of resistance syringe, it is filled with sterile saline. The loss of resistance syringe allows me to judge when I am in the epidural space, once I pass through the ligamentum flavum, there is a potential space prior to reaching the dura. This potential space causes a loss of resistance, this is felt and the anesthesiologists thumb sits on the plunger of the loss of resistance syringe. Once the loss of resistance is reached, beyond the ligamentum flavum, the plunger gives way and the anesthesiologist injects the sterile saline into the epidural space. This injection of saline into the epidural space is itself useful as it decreases the likelihood of placing your epidural catheter into an epidural vein. This procedure is all done on feel and landmarks. So, final knowledge of correct placement of the epidural only occurs once the patient begins to feel appropriately comfortable.
In the picture above to the left is the sterile saline that is used for the loss of resistance syringe. The vial in the middle is the local anesthetic that is used at the beginning of the procedure. And the vial to the right is the test dose. I will get to that in a short while. Once I have loss of resistance, I next begin to thread the epidural catheter into the epidural space. The epidural catheter is a long flexible tube that is about the thickness of a strand of spaghetti. Once the catheter is in, you may experience a shooting pain down one or both of your legs, this is typically transitory. I next dose the catheter with the test dose, the reddish vial on the right. This test dose helps confirm the epidural catheter is not in an epidural vein or in the spinal space. The anesthesiologist will typically ask if you feel any funny taste to your mouth or ringing to your ears after the test dose, this would mean the catheter is in a vein, and would need to be repositioned. The neurologic side effects are from the lidocaine in the test dose going into a vein. There is also epinephrine in the test dose and is a second signal that the catheter is malpositioned. If the patients heart rate goes up after the test dose, this means the catheter is in a vein. The lidocaine is a test to see if the catheter is in the spinal space, if after the test dose the patient becomes extremely comfortable or can't move their legs, then that means the catheter is probably intrathecal (in the spinal space).
Post epidural care:
Once the epidural is in and the test dose is done, the next thing I do is check the baseline blood pressure and start to slowly bolus the epidural catheter with Bupivacaine, a local anesthetic. I will be frequently monitoring the patient and the blood pressure to ensure each is stable. Hypotension can occur and if it does it will happen usually within the first half hour after dosing an epidural. Once I have bolused the catheter and ensured the patient is stable I begin a continuous infusion of bupivacaine and sufentanil into the epidural catheter from an external epidural pump.
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