Post-Spinal Anesthesia Side Effects
Spinal anesthesia has been used since the late-19th century to numb the lower half of the body for surgery. Cocaine was the first local anesthetic used in spinal anesthesia, but cocaine toxicity caused a lot of unwanted side effects and complications. Today, lidocaine, bupivicaine, and ropivicaine are among the most common agents used. The technique, medications, and needles have evolved over time, but there are still some post-spinal anesthesia side effects that can occur. Knowing that most of these are minor and temporary can provide peace of mind before and after your surgery.
Understanding how and why side effects of spinals occur is facilitated by understanding a little about the anatomy of the spinal area and how the technique is performed.
The spinal cord runs from the base of the brain down the middle of the back and ends in the area of the lower back, near the level of the hips. Cerebrospinal fluid (CSF) bathes the spinal cord.
A thick, fibrous membrane called the dura (yellow) covers the spinal cord and CSF- also called spinal fluid, for short. Spinal fluid may pool by gravity in the lower back inside this dura creating a sac of spinal fluid. This is sometimes called the "thecal sac" and thus, you may hear a spinal anesthetic referred to as an intrathecal anesthetic (anesthetic inside the thecal sac).
The space outside of the dura is called the epidural space. This is where epidural anesthetics are administered. The epidural space contains fat and blood vessels as well as the nerves passing through the space.
Outside of the epidural space are ligaments and other connective tissue.
The entire spinal canal is surrounded by the vertebrae that make up the backbone.
A spinal anesthetic is achieved using a thin, specialized needle to place numbing and other medications into the CSF, inside the dura. The needle is guided by "feel" between bones of the back and through the various layers of ligaments and spaces until the subdural (beneath the dura) space is reached. Drops of CSF in the hub of the needle confirm to the anesthesiologist that the needle is indeed, in the right space. The medicine is then carefully injected, and the needle removed. This medicine then numbs the nerves of the spinal cord, making it impossible to feel or move the lower half of your body.
Some post-spinal anesthesia side effects result from the technique and needle used, and some side effects of spinals are related to the medication injected.
The technique is shown in the video.
A Note about Side Effects and Complications
Side Effect vs. Complication
A side effect is an unwanted, but not unusual, effect of an intervention that accompanies the desired effect. These are usually mild and self-limited and have no long-lasting sequelae.
A complication is an event that unexpectedly occurs, as a result of an intervention. Complications cause harm, either temporarily or permanently. Most of the time, complications can be avoided, but sometimes they are unavoidable to achieve the desired effect.
Common Side Effects of Spinal Anesthesia
- Itching - Itching most often results from narcotic pain medication that is added to the numbing medicine in the spinal. The narcotic provides long-lasting (12-24 hours or more) pain relief after the numbing medicine wears off in the post-op period.
- Back Pain - Although the needle used to place the spinal is not very big, it still can make your back feel bruised at the injection site. In addition, ligament strain is not unusual. The muscles in the low-back region are completely relaxed, making stretching or straining of other structures such as ligaments more likely.
- Prolonged Numbness or Weakness - The duration of numbness with spinal anesthesia varies depending on which numbing medication is used, but should be gone within 6-8 hours in almost all cases. Occasionally, numbness can last longer. This can be a side effect or complication depending on how long it lasts and how much it impairs function.
- Urinary Retention – Some of the last nerve fibers to recover from spinal anesthesia are the ones that coordinate emptying your bladder. Urinary retention can be quite uncomfortable and can even lead to changes in heart rate and blood pressure. It may be necessary to have a catheter inserted to drain the urine if retention lasts a long time. Urinary retention is one of the more common complaints after spinal anesthesia. It is also one of the reasons we don't often do spinals on patients who are going home after their surgery.
- Nausea and Vomiting – In the first minutes after receiving a spinal anesthetic, the effects on your body occur rapidly. With the onset of the spinal, you will notice a warmness, numbness or even tingling spreading up your body. As the numbness rises, your blood vessels dilate and also, nerves of the autonomic (involuntary) nervous system are affected. These changes (and some others) cause your blood pressure to decrease. Nausea can be the first sign of this side effect. Usually, this is easily treated with IV fluids and medication; so let your anesthesiologist know if you feel queasy shortly after being given a spinal. Nausea can persist after the spinal, as well. This can be from lingering changes in blood pressure or can be related to any narcotic pain medicine that was injected.
- Headache – Some might place this into the category of complication since it has become a more rare occurrence and can be quite debilitating in the short term. It is mentioned here as a side effect, as it seems to be a fairly well known possibility and seems worth discussing. A spinal headache occurs less than 1% of the time after a spinal anesthetic and is a result of CSF leaking out of the subdural space. When the level of CSF around the brain gets low, a headache results. During a spinal anesthetic, as the dura is entered with the needle, some CSF can leak out. Our modern smaller, needles spread apart the fibers of the dura more than cut them, so the CSF leak is minimized, and so is the incidence of headache.
- Shortness of Breath – First, this is really a subjective feeling, not usually backed up by objective monitoring. When the spinal is placed for abdominal surgery, the level of numbness often needs to be quite high up into the mid-chest region to block all the involved nerves. As a necessary side effect, the spinal numbs the sensory nerves of the chest wall. We aren’t aware of it, but the feedback from these nerves let our brains know we are breathing deeply and adequately. When they are numb, especially in combination with the other factors, such as flat positioning on the operating bed, the patient may feel as if she isn’t breathing well, even when she is.
Spinal Anesthetics for Cesarean Section
Spinal anesthetics are used very often for Cesarean sections. The side effect I hear about most in these cases is shortness of breath.
During Cesarean delivery, the mom is laid flat on the bed, tilted to the left side a bit. The arms are extended out perpendicular to the body. Often the neck feels "crowded" by large breasts and a fully pregnant belly in this position. In other words, everything is pushed upwards.
It would be difficult under the best of circumstances for a full-term pregnant woman to feel like she can breathe well in this position. With the addition of a numb chest wall, it's easy to see why this feeling is so common and often can induce panic if the woman isn't reassured that the monitors show she is actually breathing well. If they still aren't convinced, I show them the fog in the oxygen mask as they breathe. This usually works well until the OB begins to push on the upper abdomen to deliver the baby. Luckily, this actual obstruction to deep breathing ends quickly and when mom hears the beautiful sound of her baby crying for the first time, she forgets all those unpleasant sensations!