Spinal Fluid Examinations: What to Expect
I’ve been practicing as a neurologist and medical doctor since the early 1990s, and I’ve done thousands of spinal fluid examinations. I know the procedure sounds painful and high-risk, but trust me, it’s anything but.
Spinal fluid examinations, or lumbar punctures, as I sometimes call them (I avoid the phrase ‘spinal tap,’ as it isn’t accurate and terrifies some folks), are only a little more involved than your standard blood test.
To ease your nerves, I’m going to walk you through exactly what to expect during this routine procedure. But first, what is spinal fluid, and why might a neurologist like me request a spinal fluid examination?
What is spinal fluid?
Cerebrospinal fluid (CSF) is a biologically active tissue, produced in the center of the brain. Once secreted by specialized tissue called choroid plexus, CSF passes through channels and aqueducts in the brain and brainstem. It also surrounds these parts of the central nervous system which seem to float in the fluid. Right now, you have about 100 to 150 ml of spinal fluid in your spinal and skull cavities.
Despite what you might imagine, healthy spinal fluid isn’t pus-like or filled with blood. It’s clear and could easily be mistaken for water.
Lumbar punctures measure distinct aspects of spinal fluid, such as the pressure it’s under, infections, and other biomarkers. Just like a blood, you can perform many different tests on spinal fluid.
Demystifying the spinal examination procedure
The more you know, the less scary it seems, right? So, let’s unpack the procedure from start to finish.
Before your lumbar puncture
To make your spinal fluid examination as comfortable as possible, I recommend arriving at my clinic well-hydrated. Drink plenty of water beforehand, and I’ll have a much easier time drawing your spinal fluid.
During your lumbar puncture
I don’t use fluoroscopy – a real-time X-ray guidance tool – to perform lumbar punctures, as I don’t find it necessary most of the time. Instead, I ask you to lie on your side with your knees as close to your chest as possible. The nurse can help you get in position if needed.
I’ll put my hand on the top of your hip bone (the iliac crest) and feel for what’s called the L4-L5 interspace. At this point, you can feel reassured knowing that, with a properly performed lumbar puncture, there is no risk of piercing the spinal cord. It has already ended.
I’ll put on some clean gloves, and we’ll start chatting. I like talking to my patients, and I want everyone to feel relaxed.
Then, I’ll use an iodine-based solution called Betadine® to scrub your skin and remove any surface bacteria. This helps prevent infection. If you’re sensitive to iodine, that’s no worry. We can use an alcohol-based disinfectant.
I’ll surround the area with sterile drapes – essentially paper towels – by placing one on top of you and tucking one underneath you and into your pant waist. You won’t be exposed during the procedure.
Numbing the area
Now, I’m ready to numb you. I’ll put on my sterile gloves and use 1% lidocaine and a very thin, 30-gauge needle to numb a small area of skin. In all honesty, this is the most painful part of the whole procedure, and it’s little more than a tickle. From here, you won’t feel anything.
After the surface of the skin is numb, I’ll take a slightly bigger syringe and, with my hand on your back, I’ll gently inject the area where the spinal needle will go. You’ll feel some pressure, and if there is any discomfort, I can take the needle out, get a little more lidocaine, numb some more, then continue the procedure. But it really is no big deal because you’re already numbed.
I’ll wait a couple of minutes for the numbing medicine to kick in. We’ll chat, and I’ll lay out the spinal fluid collection tubes on my sterile tray. The nurse may also help you keep your knees up high.
Drawing the fluid
I’ll head back into that same area, this time using a spinal fluid needle. You might be surprised by how long it looks, but don’t let that scare you. Generally, it only goes halfway in, and you won’t feel a thing.
We’ll continue our friendly conversation – How was your weekend? How are your grandkids? How’s this weather?
I’ll insert the needle, using my experience to ensure I find the precise location. There’s no guesswork involved. Then, I’ll remove the center of the needle, and spinal fluid will begin to flow.
I might measure the pressure of the spinal fluid and collect several tubes for analysis. I only draw about 10 ml or so of fluid. Most people replenish the lost spinal fluid within a few hours, so it’s nothing to be concerned about.
And that’s really it. The procedure shouldn’t keep you up at night. It’s very routine, and I’ve performed thousands. I’ll keep you safe and comfortable throughout.
What to watch out for
Elevated spinal fluid pressure
Some people overproduce spinal fluid, and that causes elevated pressure. Normal spinal fluid pressure is anywhere between 22 and 25 cm of water. When I see over 26 cm, we need to lower the pressure by removing excess fluid and prescribing medicine to maintain a lower pressure.
Too much pressure can impact your optic nerves, which connect your eyes to your brain. Over time, this can cause vision loss.
Yellow or bloody spinal fluid
Sometimes, spinal fluid looks yellow. This is not something I see in my clinic because it indicates acute spinal meningitis – and that’s a medical emergency.
Other times, spinal fluid may contain a little or a lot of blood. One of two things has occurred:
- The patient had an arachnoid hemorrhage or a burst aneurysm. Again, this is a medical emergency and not something I see at my clinic.
- The patient experienced a traumatic tap, which means the needle has caused a little trauma on its way in. (Not surprising when a needle penetrates the skin and underlying tissues.) This is not dangerous. The number of cells in the fluid is relatively low, and this not a concern.
In safe and capable hands
It’s only natural to feel anxious about your spinal fluid examination, but please don’t let the procedure prevent you from reclaiming control of your health trajectory. I have decades of experience and can help you feel comfortable, relaxed, and at ease. Contact my clinic today to schedule an appointment.