Overview of Lumbar Puncture
A lumbar puncture, sometimes called a “spinal tap,” is a routine procedure where a sample of cerebrospinal fluid (the clear liquid that surrounds your brain and spinal cord) is collected. This technique was first developed by Heinrich Quincke in the late 19th century.
This procedure is the best way to diagnose certain conditions such as meningitis, which is an inflammation of the protective membranes of the brain and spinal cord, and subarachnoid hemorrhage, a type of stroke. It can also help to diagnose certain neurological disorders, which are diseases of the brain, spinal cord, and nerves. In addition, the lumbar puncture can be used to measure the pressure inside the skull and to administer medications or substances for testing directly into the spinal fluid.
Anatomy and Physiology of Lumbar Puncture
Knowing the structure of the lower part of the spine (or lumbar spine) is important when a doctor does a lumbar puncture, which is a type of test. The doctor inserts a needle into your spine in this following order:
* Skin
* Fatty tissue under the skin
* A strong band of tissue that connects the bones of the spine (called the Supraspinous ligament)
* Another band of tissue that connects these bones (called the Interspinous ligament)
* A yellowish band of tissue (Ligamentum flavum)
* A space just outside the covering of the spine (Epidural space)
* A thick membrane that surrounds the spinal cord (Dura)
* A thin membrane around the spinal cord (Arachnoid)
* A space where there is a fluid that protects your brain and spinal cord (Subarachnoid space)
From the skin down to the epidural space, which is just outside the covering of the spine, is about 55 mm or 2/3 the length of the needle used. The Subarachnoid space, which is filled with a protective fluid called Cerebrospinal fluid (CSF) is where the sample is taken from. As the doctor moves the needle in, they usually feel a “pop” feeling. This typically happens as the needle moves through the Ligamentum flavum, the yellowish band of tissue.
Why do People Need Lumbar Puncture
A lumbar puncture, commonly known as a spinal tap, can be performed both to find answers about certain health conditions and to provide treatment. This procedure can help doctors diagnose a variety of illnesses. For instance, it might be used to identify infectious diseases that affect the brain, like encephalitis and meningitis. It can also help diagnose conditions related to inflammation, like multiple sclerosis or Guillain-Barre syndrome, which involve the nervous system. Doctors could also use a lumbar puncture to detect conditions related to cancer or metabolism, as well as subarachnoid hemorrhage, which is bleeding in the space between the brain and the surrounding membrane.
A lumbar puncture may also be used as part of some treatments – serving as a delivery method for specific drugs. This could involve administering pain relief medications, cancer treatment drugs, or antibiotics directly into the spinal fluid.
When a Person Should Avoid Lumbar Puncture
There are certain situations where a doctor might not perform a lumbar puncture, which is a procedure to collect fluid around your spine for testing. These could include:
If there’s a skin infection near where the needle would go in for the procedure, it could be unsafe to perform a lumbar puncture. It’s also unsafe if there’s a problem with the brain or spine, like a tumor, which increases the pressure in your head.
If there aren’t enough platelets in your blood, which help stop bleeding, a lumbar puncture may also be too risky. The platelet count should ideally be greater than 50,000 mm3, but a count less than 20,000 mm3 indicates a high bleeding risk.
If you’ve recently taken certain types of blood-thinning medications, like heparin, or if you have a blood disorder like hemophilia or von Willebrand’s disease that affects clotting, a lumbar puncture may not be safe. Finally, if there’s been recent damage to your spine, a lumbar puncture might not be the best choice.
In cases where there’s worry about an increase in pressure in your head, your doctor should do a head CT scan, which uses X-rays to create a detailed view of your brain, before deciding on a lumbar puncture. Symptoms that indicate increased pressure in your head may include changes in thinking or behavior, specific neurological issues like weakness or numbness in one area, a new seizure, and swelling in the optic nerve seen by a doctor during an eye exam. Other factors, like being over 60, having immune system problems, a history of cancer or certain types of brain diseases, or concerns about a brain tumor could also suggest high pressure in your head.
Equipment used for Lumbar Puncture
A Lumbar puncture kit, used to test the fluid around your spine and brain, can differ slightly based on who made it. However, every kit should have the following: a special kind of needle, called a spinal needle with a stylet, which is usually a 20 or 22 gauge needle – this is a thin, long needle designed for the procedure. There will also be four containers to collect the fluid from your spine, a sterile – or germ-free – drape to keep the area clean, a manometer which helps measure the pressure of the fluid, a three-way valve, and a local anesthetic to numb the area where the needle is inserted.
Additionally, the kit will have syringes with different size needles (typically 18-gauge to pick up the anesthetic and 25-gauge to inject into the skin), a disinfecting solution, sterile gloves, a mask with a face shield and a surgical cap for the medical professional to wear. All of these are used to ensure that the procedure is as clean and free of germs as possible.
There are different types of needles that can be used, but it’s generally suggested to use a Whitacre spinal needle over a Quincke spinal needle. The Whitacre needle, also known as a pencil-point needle, is seen as better because it causes fewer complications. Before this needle can be inserted, the skin needs to be punctured.
Who is needed to perform Lumbar Puncture?
A lumbar puncture, also known as a spinal tap, is usually done by one person, often a doctor. A nurse may be there too, helping the doctor. Both of them wear clean special gowns throughout the procedure to keep everything sterile, which means free from any germs. They take these precautions to make sure the procedure is safe and clean. This way, they prevent any potential infections that could complicate your health while the procedure is being performed.
Preparing for Lumbar Puncture
Before any medical procedure, proper preparation ensures safety and success. For example, before carrying out a procedure known as a lumbar puncture (a test where a needle is inserted into the lower part of the spine to collect fluid), a doctor has to check for anything that might make the procedure unsafe. This includes checking for any signs or risk factors for conditions such as high pressure in the skull, bleeding disorders, or low platelet levels (a type of blood cell that helps with clotting).
Doctors carry out lumbar punctures for various reasons and should always make sure it is necessary by reviewing the different reasons for the test. Importantly, patients should understand what the procedure involves as well as the risks and benefits. A doctor should explain these details, and get the patient’s consent before carrying out the operation.
During a lumbar puncture, a patient can either lie on their side or sit up. Generally, lying on the side is recommended because it allows for accurate pressure measurements and can also reduce the risk of a headache after the procedure. Patients are asked to curl up, similar to a “fetal” position, which involves bending the spine. The doctor may suggest to the patient to curve their back “like a cat”; this will make more room for the needle to be inserted into the spine. The best spot for inserting the needle is either between the fourth and fifth or between the third and fourth bones in the lower spine. This positioning can help avoid damage to the spinal cord.
The location for needle insertion may be harder to find in people who are obese, or those with a curved spine or a degenerative disc disease. Once the right spot has been found, a line—called the intercristal line or Tuffier line—that typically aligns with the fourth bone of the lower spine, is drawn between the top parts of the hip bone.
Lumbar puncture is a sterile procedure, meaning that doctors use clean instruments and protective clothing to avoid infection. The doctor will clean the skin around the area where the needle is to be inserted with a disinfecting agent and then cover it with sterile drapes. Bags will be prepared for collecting spinal fluid.
Before the procedure begins, a local anesthetic will be applied to numb the area where the needle will be inserted. It’s important to mark the spot for needle insertion before the local anesthetic is applied because the anesthetic can make identifying the spot difficult.
How is Lumbar Puncture performed
Before the needle enters the spine, the doctor will re-identify the key features of your body. The needle is inserted along a line in the middle of your body, following certain points on the bones in your lower back. The needle enters the skin at an angle of about 15 degrees and is aimed towards your belly button. This is done while a part of the needle called the stylet is still inside it and the part known as the bevel is positioned such that it is facing up if you are lying on your side. This direction is chosen because it separates, rather than cuts through, the fibers of your cauda equina, a strand of nerve roots at the end of your spinal cord that resembles a horse’s tail . These fibers are arranged lengthways along your spinal cord.
The needle slides into your spine smoothly, in one direction. There may be a little resistance, like a “pop,” when the needle is passing through a ligament in the spine called the ligamentum flavum. After this the needle keeps moving in little steps, removing the stylet each time to check for cerebrospinal fluid (CSF) flowing out. This is one sign that the needle has reached the right point in the spine. When bone is struck or if there is no return of CSF fluid flowing out, then the needle is pulled almost all the way out, though not completely out of the skin, before being corrected in its direction. Not doing so increases the risk of a traumatic lumbar puncture or a spinal tap that results in bleeding and blood mixing with the CSF. If this happens or if the needle gets blocked by too much blood, a new one will be used at a slightly different position.
In some cases, it is hard to get the CSF from the original needle entry point. In such situations, a different location may be tried. Sometimes ultrasound guidance is used to make the procedure more successful. Another technique called the paramedian approach could be used to reach the right spot in your spinal cord where the CSF is found. This is taken as an option if the usual method, called the median approach, does not work. Using the paramedian approach, instead of going straight downwards, the needle is inserted slightly to the side, then pushed medially (towards the center of the body) and upwards at an angle of 15 degrees until the CSF starts flowing out.
Once the needle enters the right area of the spinal cord where the CSF is found (known as the subarachnoid space), CSF will start to flow out. If the doctor wants to measure the pressure of the fluid, known as the opening pressure, this is done while you are lying on your side to get an accurate reading. A special meter, known as a manometer is attached to the needle with a flexible tube. The CSF will rise in the meter, and the doctor will note the height at which it stops rising. The normal level is between 6 cm and 25 cm of water column. Very minor variations might occur due to your breathing. After recording the opening pressure, the meter is unhooked, and the CSF will drain out from the needle hub into collection tubes. No suction is applied to extract the CSF because it flows out naturally. Often about 1 ml of CSF is collected for each vial to be studied in the lab.
Once CSF has been collected, the stylet is placed back into the needle, and the whole needle is then withdrawn. Gentle pressure is applied over the needle entry point with a sterile piece of gauze and the area is covered with a small bandage.
All sharps are then tossed into their special waste disposal containers.
Possible Complications of Lumbar Puncture
Let’s talk about the potential risks and complications that could happen after a procedure called a lumbar puncture. Knowing what could happen is really important and should be explained before the procedure. Sure, serious complications are pretty rare, but even then, we can lower the risk even further by being careful and using the right techniques.
Some complications can include headaches after the procedure, bleeding, infection, blood accumulating in the spinal area, and a condition where the brain gets squeezed (cerebral herniation). The most common thing that happens after a lumbar puncture is a headache. Medical studies have shown that if the medical needle has a pencil-like point and is thin, it’s less likely to cause a headache than a needle which has a cutting edge. Also, removing the spinal needle carefully can reduce the chances of having headaches after the procedure.
There’s also a risk of spinal hematoma, which is when blood collects in the spinal area. This happens more often in patients who have a trouble with their blood not clotting properly or are taking certain blood thinners. If this happens, the patient might feel acute back pain or notice new issues related to their nervous system. If doctors suspect this kind of complication, they can use a technique called an MRI (magnetic resonance imaging), which can give them a detailed picture of the brain and confirm the diagnosis.
What Else Should I Know About Lumbar Puncture?
A lumbar puncture, often referred to as a “spinal tap,” is a common procedure performed in emergency departments. This is a test doctors use to diagnose serious illnesses such as meningitis (an inflammation of the membranes covering the brain and spinal cord) and subarachnoid hemorrhage (bleeding in the space surrounding the brain). Understanding the detailed structure of the body parts involved, the possible risks, and the different ways to do this procedure is vital to performing a successful and safe lumbar puncture.
Speaking with the patient throughout the procedure can help to reduce their worry and increase the likelihood of a successful test on the first attempt. A lumbar puncture involves inserting a needle into the lower back to get a sample of spinal fluid, which is then tested in a lab. It’s important for patients to understand what’s happening, why it’s happening, and what the possible outcomes and risks are, so that they can provide informed consent and help the procedure run smoothly.
