When I tell patients they need a lumbar puncture, many of them have heard about it or already know about it somehow through experiences involving friends or family, but they usually think it is more of an event than it actually is. I don't want to minimize the procedure... but when I was a resident, I would often do at least one to a few each night I was on call. I would drop by, do the procedure in the Emergency Room or in the patient's room on the floor or ICU, be in and out in 10 minutes or less. Usually the nurses or younger resident on call would spend longer preparing the patient for the procedure than I did actually performing it.
An LP (Lumbar Puncture), also known as a spinal tap, is important in the diagnosis of infections and certain inflammatory disease such as multiple sclerosis, Guillain-Barre syndrome, vasculitis, certain types of headaches, certain malignant conditions...
CSF (cerebro-spinal fluid) is the fluid that surrounds your brain and spinal cord. It is also what we must take a further look at when we do our lumbar puncture.
People's number one concern is that I'm going to paralyze them, or could paralyze them potentially. The reality is that your spinal cord ends at least a hand's width ABOVE where I put the needle. Now, some nerves still come down on their way to your legs, but the most that will happen is that I could swipe one of those nerves and you will feel pain into one of your legs briefly. I say briefly because the nerve is floating in your cerebrospinal fluid and will therefore roll out of the way if my needle brushes it.
A spinal tap is performed in the space between the lumbar vertebrae which are there to protect your spinal cord from injury. It's a testament to how well they do their job, that it takes so much effort and preparation for me to fit a relatively skinny needle between their tight-fitting junctions. Usually the needle is inserted at the L3-L4 level, or more likely the L4-L5 level.
Your spinal column ends at the L1 level in adults
Preparation
The spinal needle used is disposable. It looks long, and is... but usually only a small part of it needs to actually go into the back. It is long because sometimes it, frankly, has to go through the muscle and fat of your back which can be thick.
Sedative medications can be used but are rarely needed because usually the local anesthetic is enough.
The bed should be flat, and the patient should be lying on his/her side. The patient's body needs to be perfectly perpendicular to the bed, in other words not twisted at all, which would twist the vertebrae slightly and make them harder to squeeze between. The patient should assume the fetal position with knees flexed to the chest as much as possible.
The low back is cleaned well with strong, surgical grade anti-bacterial medication, and then covered with a sterile drape to isolate the area.
Procedure
Local anesthetic is used numb the area well before the long needle is put in. The local anesthetic burns, I confess, but briefly and not that much actually.
The spinal needle then is positioned between the 2 vertebral spines at the L3-L4 or L4-L5 level and put into the skin with the bevel of the needle facing up.
Accurate placement of the needle is rewarded by a flow of fluid, which normally is clear and colorless.
As with any procedure, experience improves the success rate. One of the primary goals is to prevent the introduction of blood into the CSF sample.
A measurement of opening pressure should be made; the normal range is 80-180 mm H2O.
Following determination of CSF pressure, CSF samples should be taken.
You can see, this is the fluid once collected. I took these pictures last week with the patient's permission of course. As you can see, the fluid is clear and colorless in the two right tubes. The first tube has the slightest shade of pink from a capillary I passed on the way in. It's hard to avoid those sometimes since they supply every cell.
Okay, things to note here: That red stuff is NOT BLOOD. It is Betadine, the antiseptic that kills off the bacteria around the puncture site. It is actually brown. But, you can see here that even though the needle looks long (You can maybe tell in the tray below this picture), usually only a small part of it needs to go inside.
This Lumbar Puncture took me 8 minutes to do, and took me 15 minutes to properly prepare for.
And this is the Lumbar Puncture kit (already used in this picture). You can see the brown Betadine ready for me to use, some swabs, the opening pressure tubing on the left, the long needle stylus in the middle below with a pink end, and the numbing medication syringe at the very bottom, and of then the top view of 3 out of 4 of the tubes I collect your cerebrospinal fluid in. It comes completely sealed and sterile.
Collecting the fluid and some stuff we look for in the fluid:
If the fluid appears to be bloody, several specimens should be collected. If the blood clears in successive tubes then the blood, at least in part, was traumatic in origin.
When sufficient fluid is obtained, the needle is withdrawn and a dry sterile dressing applied to the puncture site. Prolonged compression of the site, or keeping you on your back for an extended period, has not been proved to reduce the incidence of spinal headache... but we do it anyway.
Separate specimens should be sent for microscopic study and for biochemical analysis as well as other specific tests (such as oligoclonal band testing) if required for such things as multiple sclerosis among other things. Normal CSF may contain as many as 5 white blood cells (WBCs)s per cubic millimeter.
A larger-than-usual number of WBCs suggests infection or inflammation or, neoplastic infiltration.
A traumatic tap will, of course, introduce both WBCs and RBCs into the CSF.
An approximation of 1 WBC per 700 to 1000 RBCs can be made, although a repeat tap may be preferable.
Other tests
Assuming the CSF has been collected under sterile conditions, microbiologic studies can be performed. Stains, cultures, and immunoglobulin titers can be obtained. The latter are of special importance in diseases in which peripheral manifestations fade while CNS symptoms persist (eg, syphilis, Lyme disease).
Assessment of CSF protein level, while nonspecific, can be a clue to otherwise unsuspected neurologic disease. The high protein levels in demyelinating polyneuropathies , or postinfectious states, can be informative. A traumatic tap can introduce protein into the CSF.
An approximation of 1 mg of protein per 750 RBCs may be used, although a repeat tap is preferable.
CSF glucose level normally approximates 60% of the peripheral blood glucose level at the time of the tap. A simultaneous measurement of blood glucose (especially if the CSF glucose level is likely to be low) is recommended. Low CSF glucose level usually is associated with bacterial infection (probably due to enzymatic inhibition rather that actual bacterial consumption of the glucose). It also is seen in tumor infiltration, and may be one of the hallmarks of cancerous invasion of the lining of the brain (meningeal carcinomatosis), even with negative cytologic findings.
Leptomeningeal malignancies: Multiple lumbar punture examinations may be required in this situation. At least 3 negative cytologic evaluations (ie, 3 separate samplings) are required to rule out leptomeningeal malignancy (eg, leptomeningeal carcinomatosis). You are looking for a few abnormally formed white blood cells in this condition, so you need a lot of fluid to find one.
Risks associated with a Lumbar Puncture
- Post–spinal tap headache
This headache is characterized by pulsatile head pain , with or without nausea, relieved by lying down and aggravated by standing and "Valsalva" maneuvers such as coughing and straining at stool. It is self-limited but may last up to a week (or rarely longer). The placement of an epidural blood patch using the patient's own venous blood often corrects this problem. However, the need for a blood patch is uncommon. The use of intravenous caffeine benzoate (500 mg infusion over 1 h) also has been found to treat post Lumbar-Puncture headaches effectively in double-blind, controlled trials. Or, more commonly, you can drink some caffeine or take 600mg capsules of caffeine which can help (BUT make sure your doctor recommends this first before your start "juicing" up on caffeine).
- Nerve root trauma
· This may cause temporary pain or tingling in the skin from which the nerve root is transmitting information (i.e. the "dermatome" of that particular nerve root).
- CNS infection (rare)*and we are often LOOKING for infection
- Bleeding (rare) and usually minimal when occurs
- Local pain from going through the back skin/fat/muscles.... in reality, this is usually more from the fear of complication and pain than actual trauma from a needle less than a millimeter in width
- Other complications of Lumbar-Puncture such as paralysis are incredibly rare if the procedure is done by an experienced physician
The ongoing headache you should know about:
-A post LP headache can last 4 to5 days. IF it's getting worse though, you may need a blood patch, in which a little blood is put into the area of lumbar puncture to clot the area. It happens, but thankfully I've either personally done, or sent patients for, hundreds of these and never had this complication. But, it's actually as easy to do as the initial LP, just in reverse.
-Usually, if the headache goes on too long, I recommend bed rest, Tylenol, and caffeine for a little longer than expected, even though almost everyone can go back to work within an hour after their LP.
