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Description
Lumbar puncture is performed by inserting the needle between the fourth and fifth lumbar vertebrae (L4-L5). This location is used because the spinal cord stops near L2, and a needle introduced below this level will miss the cord. In rare instances, such as a spinal fluid blockage in the middle of the back, a physician may perform a spinal tap in the cervical spine.
Precautions
In some circumstances, a lumbar puncture to withdraw a small amount of CSF for analysis may lead to serious complications. Lumbar punctures should be performed only with extreme caution and only if the benefits are thought to outweigh the risks. In people who have bleeding disorders, lumbar puncture can cause hemorrhage that can compress the spinal cord. If there is increased spinal column pressure, as may occur with a brain tumor and other conditions, removal of CSF can cause the brain to herniate, compressing the brain stem and other vital structures and leading to irreversible brain damage or death. Meningitis may be caused by bacteria introduced during the puncture. For this reason, aseptic technique must be followed strictly, and a lumbar puncture should never be performed at the site of a localized skin lesion.
Specimens should be handled with caution to avoid contamination with skin flora. They should be refrigerated if analysis cannot be performed immediately.
Aftercare
After the procedure, the site of the puncture is covered with a sterile bandage. The patient should remain lying for four to six hours after the lumbar puncture. Vital signs should be monitored every 15 minutes for four hours, then every 30 minutes for another four hours. The puncture site should be observed for signs of weeping or swelling for 24 hours. The neurological status of the patient should also be evaluated for such symptoms as numbness and/or tingling in the lower extremities.
Risks
The most common side effect after the removal of CSF is a headache. This occurs in up to 40 percent of children. It is caused by a decreased CSF pressure related to a small leak of CSF through the puncture site. These headaches usually are a dull pain, although some people report a throbbing sensation. A stiff neck and nausea may accompany the headache. Lumbar puncture headaches typically begin within two days after the procedure and persist from a few days to several weeks or months.
Normal results
The normal results include the following:
- gross appearance: normal CSF, clear and colorless
- CSF opening pressure: in children older than six to eight years, 90–180 mm H2O; in infants and younger children, 10–100 mm H2O
- specific gravity: 1.006–1.009
- glucose: 40–80 mg/dL
- total protein: 15–45 mg/dL
- LD: 1/10 of serum level
- lactate: less than 35 mg/dL
- leukocytes (white blood cells): 0–6/microL (adults and children); up to 19/microL in infants; up to 30/microL (newborns)
- differential: 60–80 percent lymphocytes; up to 30 percent monocytes and macrophages; other cells 2 percent or less. Monocytes and macrophages are somewhat higher in neonates, and make up as much as 80 percent or more, with only 20 percent or less being lymphocytes.
- Gram stain: negative
- culture: sterile
- syphilis serology: negative
- red blood cell count: normally, none unless the needle passes though a blood vessel on route to the CSF
Parental concerns
If the child is anxious or uncooperative, a short-acting sedative may be given. Patients receive a local anesthetic to minimize any pain in the lower back from inserting the needle.
When to call the doctor
If the child does not respond to the parents, if the puncture site continues to leak a watery fluid, or the puncture site appears red and swollen, or has other signs of infection, then the doctor should be notified.
KEY TERMS
Demyelination—Disruption or destruction of the myelin sheath, leaving a bare nerve. It results in a slowing or stopping of the impulses that travel along that nerve.
Encephalitis—Inflammation of the brain, usually caused by a virus. The inflammation may interfere with normal brain function and may cause seizures, sleepiness, confusion, personality changes, weakness in one or more parts of the body, and even coma.
Guillain-Barré syndrome—Progressive and usually reversible paralysis or weakness of multiple muscles usually starting in the lower extremities and often ascending to the muscles involved in respiration. The syndrome is due to inflammation and loss of the myelin covering of the nerve fibers, often associated with an acute infection. Also called acute idiopathic polyneuritis.
Meningitis—An infection or inflammation of the membranes that cover the brain and spinal cord. It is usually caused by bacteria or a virus.
Multiple sclerosis—A progressive, autoimmune disease of the central nervous system characterized by damage to the myelin sheath that covers nerves. The disease, which causes progressive paralysis, is marked by periods of exacerbation and remission.
Spinal canal—The opening that runs through the center of the spinal column. The spinal cord passes through the spinal canal. Also called the vertebral canal.
Subarachnoid—Referring to the space underneath the arachnoid membrane, the middle of the three membranes that sheath the spinal cord and brain.
Treponeme—A term used to refer to any member of the genus Treponema, which is an anaerobic bacteria consisting of cells, 3–8 micrometers in length, with acute, regular, or irregular spirals and no obvious protoplasmic structure.
Vertebrae—Singular, vertebra. The individual bones of the spinal column that are stacked on top of each other. There is a hole in the center of each bone, through which the spinal cord passes.
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Author Info: Mark A. Best, Thomson Gale, Gale, Detroit, Gale Encyclopedia of Children's Health, 2006 |
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