Spinal Tap (Lumbar Puncture)
What Is a Spinal Tap/Lumbar Puncture?
A lumbar puncture, or 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.
Doctors use the fluid sample to look for signs of possible infections or other illnesses.
Why Are Spinal Taps Done?
The central nervous system is made up of the brain and spinal cord. It's the "command center" for the body. The spinal cord sends signals to and from the brain and the brain interprets them.
Cerebrospinal fluid constantly flows around the central nervous system while protecting it. Becausee 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. So a lumbar puncture can help doctors find or rule out many diseases or conditions.
Most often, a spinal tap is done is to see 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 affects the nervous system, and bleeding in the brain.
Spinal taps also can be used to add medicine, anesthesia, or dye (for specialized X-rays) directly into the cerebrospinal fluid. Occasionally, they're done to help relieve pressure in the brain when a condition causes the body to make too much CSF.
What Happens Before a Spinal Tap?
If your child needs a lumbar puncture, you'll have an opportunity to ask questions first. Then, you'll be asked to sign an informed consent form, stating that you understand the procedure and its risks and give your permission for it.
Most spinal taps are done in the emergency department. The doctor doing it will know your child's but might ask a few questions, such as whether your child is allergic to any medicines.
Some parents choose to be in the room with their child during the spinal tap, while others are more comfortable in a waiting area. You can ask the doctor if it is OK for you to stay.
What Happens During a Spinal Tap?
A spinal tap is a common procedure that takes about 30 minutes or less.
The spinal cord extends from the lower part of the brain down to the upper lumbar area. A spinal tap is done in the lower lumbar area, below the point where the spinal cord ends. So, the risk of harming the spinal cord is avoided.
A lumbar puncture is not a surgery. So someone getting one might be awake during it, and won't need stitches or extended recovery time. If a child seems anxious or agitated, the 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.
Patients should 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 position, a doctor will use sterilizing soap to clean the area where the needle will go in.
A small area on the lower back is numbed by a type of liquid anesthesia (medicine that helps prevent pain) given through a tiny needle. Often, a numbing cream is applied to the skin before this. The cream eases the discomfort of the injection, although the liquid medicine may burn a little.
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. 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, letting the CSF drip 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. When 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).
Collecting the CSF sample usually takes about 5 minutes. Then, the needle is withdrawn and a small bandage is placed on the site. Collected samples are sent to a lab for testing.
What Happens After a Spinal Tap?
If you were not in the room with your child during the test, you can 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.
Some results are available within 30 to 60 minutes. But to look for specific bacteria growing in the sample, a bacterial culture is sent to the lab. These results are usually available in 48 hours. If there might be an infection, the doctor will start antibiotic treatment while waiting for the culture results.
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.
Lab technicians also do a Gram stain and culture on the sample. A Gram stain detects bacteria in a sample. This involves adding a kind of dye to it, then checking it for bacteria. Then the sample is cultured (put in special conditions to see if any germs grow from the CSF). This helps identify the specific type of infection.
What Are the Risks of a Spinal Tap?
A spinal tap is a safe procedure with few, if any, risks. Rarely, complications can include:
- Headache: After a lumbar puncture, a patient should lie down for a few hours and drink plenty of fluids, which can help prevent a headache. Babies do not need to do this. If your child gets a headache, acetaminophen or another non-aspirin type of pain reliever usually helps. If a headache lasts for more than 2 days, call your doctor.
- Infection: In rare cases, infection can happen if bacteria get into the skin when the puncture is done. This is very rare because doctors always use sterile techniques to do 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 spinal taps are brief, common procedures and complications are rare. If you have any questions or concerns, talk with your doctor.