A lumbar puncture (also called a spinal tap) is a medical test that involves collecting a small sample of cerebrospinal fluid (CSF) for examination. This clear, colorless liquid helps "cushion" the brain and spinal cord, or central nervous system.
Words like "puncture" and "tap" seem intimidating, but the concept of a lumbar puncture (LP) is actually similar to a blood test. Doctors use the fluid sample to look for signs of possible infections or other illnesses.
While some notice a brief pinch and a slight burning sensation, most people don't consider a lumbar puncture to be painful. Still, any procedure that involves a needle is likely to cause some anxiety for a child, so it helps to understand how this test is performed. That way you can feel confident about what is happening and help put your child at ease.
About Lumbar Puncture
While its name might sound scary, a lumbar puncture is actually a common procedure that only takes about 30 minutes or less. A doctor carefully inserts a thin hollow needle between two of the bones of the lower spine (below the spinal cord) to withdraw the fluid sample for testing in a lab.
The lumbar area is a region of the spine (backbone), which is made up of 33 ring-shaped bones called vertebrae. One of the main functions of the spine is to protect the spinal cord, a bundle of nerve fibers that transmit messages to and from the brain.
The spinal cord extends from the lower part of the brain down to the upper lumbar area. A lumbar puncture is done in the lower lumbar area, below the point where the spinal cord ends. So, with an LP, the risk of harming the spinal cord is avoided.
Why Cerebrospinal Fluid Is So Important
The central nervous system is made up of the brain and spinal cord; it functions as the "command center" for the body. The spinal cord sends signals to and from the brain and the brain interprets them.
Cerebrospinal fluid continuously flows around the central nervous system while protecting it. Since it "bathes" the central nervous system, CSF can also pick up chemicals and impurities in the brain and spinal cord.
A fluid sample can provide a lot of important information about a person's health. Analyzing it for things like bacteria, white blood cell count, glucose levels, protein, or abnormal cells can help experts identify specific diseases in the central nervous system.
Why Does My Child Need a Lumbar Puncture?
Although a lumbar puncture tests for fairly serious diseases and conditions, it's also a tool to make sure a person doesn't have a certain disease or condition. So even if your child needs an LP, this doesn't necessarily mean he or she has a particular illness.
By performing a lumbar puncture and testing the CSF, experts can detect or rule out suspected diseases or conditions. The most common reason a lumbar puncture is done is to determine if a child has meningitis (inflammation and infection of the covering of the brain and spinal cord). Other conditions that can be detected include Guillain Barré syndrome, multiple sclerosis, cancer that has affected the nervous system, and bleeding in the brain.
LPs also can be used to add medicine, anesthesia, or dye (for specialized X-rays) directly into the cerebrospinal fluid. Occasionally, a lumbar puncture is performed to help relieve pressure in the brain caused by conditions that make the body produce too much CSF.
Preparing for a Lumbar Puncture
Once it's determined that your child needs a lumbar puncture, you'll have an opportunity to ask questions. When you feel comfortable with the information and your questions have been fully answered, you'll be asked to sign an informed consent form, stating that you understand the procedure and its risks and give your permission for the lumbar puncture.
Most spinal taps are done in the emergency department. The doctor performing the LP will know your child's medical history but might ask a few additional questions, such as whether your child is allergic to any medicines.
A pulse oximeter (or pulse-ox, which resembles a Band-Aid and is attached to a fingertip to measure the blood oxygen level) is used during most spinal taps.
Some parents choose to be in the room with their child during the LP while others are more comfortable stepping outside to a waiting area. You can ask the doctor if it is OK to be present.
During the Procedure
A lumbar puncture is a procedure, not a surgery. So someone getting an LP may be awake through the procedure and won't need stitches or extended recovery time. However, if a child seems to be anxious or agitated, a doctor will recommend a sedative (a type of medicine that helps the patient relax during the procedure). The sedative can be given by mouth, nose, or through an IV.
How the patient is positioned is the most important detail in getting ready for a lumbar puncture. It's important for the patient to be positioned with the back curved out so the spaces between the vertebrae are as wide as possible. This makes it easier for the doctor to insert the needle.
Older children may be asked to either sit on an exam table while leaning over with their head on a pillow or lie on their side. Infants and younger children are positioned on their sides with their knees under their chin. For these children, nurses or aides hold them securely in position.
When the patient is in the desired position, a doctor will use sterilizing soap to clean the area where the needle will go in.
Before the LP is performed, a small area of skin on the lower back is numbed by a type of liquid anesthesia (medicine that helps prevent pain). This is provided through a tiny needle. In many cases, before the injected anesthesia medication is given, a numbing cream is applied to the skin. The cream lessens the discomfort of the injection, although the liquid medicine may burn a little.
Once the preparations are complete and the injected anesthesia takes effect (usually within a few minutes), the actual lumbar puncture procedure can begin.
The Spinal Needle
The spinal needle is the most important tool of this procedure, and functions as the "tap." The needle is thin and the length varies with the size of the patient. It has a hollow core, and inside the hollow core is a "stylet," another type of thin needle that acts kind of like a plug. When the spinal needle is inserted into the lower lumbar area, the stylet is carefully removed, which allows the CSF to drip out into the collection tubes.
"Tapping" the Cerebrospinal Fluid
Making sure the patient is in the proper position, a doctor carefully inserts the spinal needle between two vertebrae. The needle is carefully passed through skin and ligaments, and then through a tough membrane called the dura mater. Doctors can tell that the needle is in the right place when they feel a “pop” which means the needle passed through the tough membrane. Once the needle reaches an area called the spinal canal, the stylet is slowly pulled out to allow the cerebrospinal fluid to flow.
Occasionally, a small tool called a manometer is hooked up to the end of the needle. A manometer is basically a gauge that measures pressure of the CSF. High fluid pressure can be an indicator of some serious conditions, like tumors or hydrocephalus (excessive buildup of fluid in the brain).
After the sample is collected (this usually takes about 5 minutes), the needle is withdrawn and a small bandage is placed on the site. Collected samples are sent to a lab for further analysis and testing.
If you were not in the room with your child during the test, you'll be able to come in after the samples have been collected. Depending on the doctor's recommendations, your child might have to lie down on his or her back for an hour or so after the procedure.
After the Procedure
Some results from a lumbar puncture are available within 30 to 60 minutes. However, to look for specific bacteria growing in the sample, a bacterial culture is sent to the lab and these results are usually available in 48 hours. If it's determined there might be an infection, the doctor will start antibiotic treatment while waiting for the results of the culture.
Lab technicians look for several things when examining the cerebrospinal fluid sample, including:
- General appearance: CSF is usually clear and colorless like water. Cloudy spinal fluid or any blood in the sample may indicate an infection or other problem.
- Cell count: This includes the number and type of white blood cells. Too many white cells indicate an infection.
- Protein: Large amounts of protein in the CSF can suggest an infection or other diseases.
- Glucose: In bacterial infections of the central nervous system, the glucose level of the CSF is sometimes low.
In addition, lab technicians will perform a Gram stain and culture on the sample. A Gram stain, which detects bacteria in a sample, involves adding a kind of dye to the collected cerebrospinal fluid. This "stained" sample is then examined under the microscope to look for bacteria. The sample is then cultured (put in special conditions to see if any germs grow from the CSF). This helps identify the specific type of infection.
Risks and Complications
A lumbar puncture is considered a safe procedure with minimal, if any, risks. Most of the time, there are no complications. In rare instances, complications can include:
- Headache: After a lumbar puncture, it's recommended that a patient lie down for a few hours and drink plenty of fluids, which can help stop the onset of a headache. Babies do not need to do this. However, if your child develops a headache, acetaminophen or another non-aspirin type of pain reliever usually helps. If a headache persists for more than 2 days, call your doctor.
- Infection: In rare cases, infection can occur if bacteria are introduced into the skin when the puncture is done. This is very rare because doctors always use sterile techniques to perform the test.
- Bleeding: If a small blood vessel under the skin is nicked during the spinal tap, there may be some bleeding.
When your child is having any kind of procedure, it's understandable to be a little uneasy. But it helps to know that lumbar punctures are brief, common procedures and complications are rare. If you have any questions or concerns about the lumbar puncture procedure, talk with your doctor.