A lumbar puncture (LP), sometimes called a spinal tap, is a procedure in which a small amount of the fluid that surrounds the brain and spinal cord, called the cerebrospinal fluid (CSF), is removed and examined.
In infants and children, a lumbar puncture is typically done to look for meningitis, an infection of the meninges, which is the membrane covering the brain and spinal cord. There are other reasons to do lumbar punctures, too: They may be performed to remove fluid and relieve pressure with certain types of headaches, to look for other diseases in the central nervous system, or to place chemotherapy medications into the spinal fluid.
What Happens During a Lumbar Puncture?
There are steps to make sure that a child doesn't feel pain during the lumbar puncture. For a nonemergency LP, a nurse will rub a topical anesthesia cream on the skin of the back where the LP will be done about 30 minutes to 1 hour before. When the needle goes into the skin, the child won't feel sharp pain, only perhaps some pressure. After the skin is numbed, some doctors also inject liquid anesthesia such as lidocaine into the tissues right under the skin to prevent any further pain.
After the preparation has been completed, the child is positioned on an exam table so that the spaces between the vertebrae (bones of the spine) are as wide as possible. Infants and small kids lie on their sides curled up with their knees under their chin, like the letter C. (Sometimes nurses or aides have to hold kids in the position in order to get the best test results.) Teens may lie down or sit with their heads resting on a pillow placed on a table at waist level.
Next, the doctor places a small needle through the skin and then forward through the space between the vertebrae in the lower back until it enters the space that contains the spinal fluid. The spinal fluid drips out through the needle into tubes, is collected, and sent to a lab for analysis. The pressure in the brain (intracranial pressure) can also be measured as part of the test, which can provide important information in some situations. After the sample is collected (usually this takes several minutes), the needle is withdrawn and a bandage is placed on the site.
It is important to note that the needle does not enter the spinal cord or nerves because the test is done in the lower back, below the level to which the spinal cord extends.
Understanding the Results
Fluid collected from a lumbar puncture is immediately sent to the laboratory and analyzed for evidence of an infection. Some of the results are available within 30 to 60 minutes. However, bacterial culture is necessary to watch for an organism growing in the sample. Culture results are usually available in 48 hours. If the doctor determines that the child has an infection, he or she will start antibiotic treatment while waiting for the results of the culture and then make any necessary adjustments once the final results come in.
The lab technicians look for a number of things when examining the spinal fluid sample, including:
- General appearance: CSF is usually clear and colorless and looks like water. Cloudy spinal fluid may indicate infection because of increased cells and proteins suspended in the fluid.
- Cell count: This includes the number and type of white blood cells and the number of red blood cells present. CSF normally does not contain either of these types of cells. The presence of too many white cells indicates an infection.
- Protein: Large amounts of protein in the spinal fluid also suggest an infection or other disease.
- Glucose: In bacterial infections of the spinal fluid, the glucose level of the fluid is often low.
- Gram's stain and culture: CSF is also stained and examined under the microscope to look for bacteria. The staining technique used, called the Gram's stain, detects bacteria in the CSF. To confirm an infection, it is also cultured to see if any organisms grow from the fluid.
- CSF may also be processed for other tests for which results are not available immediately.
Complications From Spinal Taps
Most of the time, there are no complications with spinal taps. In the rare instances when they do occur, complications can include:
- Headache: This can occur because of continued leaking at the site where the fluid was taken. If this occurs, you may want to give your child acetaminophen or another non-aspirin type of pain reliever. If the headache persists for more than 2 days, call your child's doctor.
- Infection: In rare cases, it's possible to cause an infection 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.
Again, these complications are uncommon. If you have any other questions or concerns about your child following a spinal tap, contact your child's doctor.
Reviewed by: Kate Cronan, MD
Date reviewed: October 2005
Originally reviewed by: Frederick A. Meier, MD, and Neil Izenberg, MD
No comments:
Post a Comment