In medicine, a lumbar puncture (or spinal tap) is a diagnostic
procedure that is done to collect a sample of cerebrospinal fluid (CSF)
for biochemical and microbiological analysis. Lumbar puncture may also
be done to inject medications into the cerebrospinal fluid. The most
common indication for a lumbar puncture is to collect cerebrospinal
fluid in a case of suspected meningitis.
A lumbar puncture must be done with aseptic technique by qualified
In performing a lumbar puncture (in an adult), first the patient is
usually placed in a left (or right) lateral position with his/her neck
bent in full flexion and knees bent in full flexion up to his/her
chest, approximating a fetal position as much as possible. It is also
possible to have the patient sit on a stool and bend his/her head and
shoulders forward. The area around the lower back should be prepared
using aseptic technique. Once the appropriate location is palpated, a
spinal needle is inserted, usually between the lumbar vertebrae L3/L4
or L4/L5 and pushed in until there is a "give" that indicates the
needle is past the dura mater. The stylet from the spinal needle is
then withdrawn and drops of cerebrospinal fluid are collected. The
opening and closing pressures of the cerebrospinal fluid may be taken
during this collection. The procedure is ended by withdrawing the
needle while placing pressure on the puncture site. The patient should
then lie on his/her back for at least six hours and be monitored for
any signs of neurological problems. The technique described is almost
identical to that used in spinal anesthesia, except that spinal
anesthesia is more often done with the patient in a sitting position.
Adverse side effects from a lumbar puncture range from introduced
infection to headache. Headache is the most common complication.
Serious complications of a lumbar puncture include damage to the
spinal cord or spinal nerve roots resulting in weakness or loss of
sensation, or even paraplegia.
The procedure is not recommended when epidural infection is present or
suspected, when topical infections or dermatological conditions pose a
risk of infection at the puncture site or in patients with severe
psychosis or neurosis with back pain. Elevated or reduced pressure in
the brain also poses risks during lumbar punctures. Withdrawal of
fluid when initial pressures are too low could result in spinal cord
compression or cerebral hernia.
Removal of cerebrospinal fluid resulting in reduced fluid pressure has
been shown to correlate with greater reduction of cerebral blood flow
among patients with Alzheimers disease.
Patient anxiety during the procedure can lead to increased CSF fluid
pressure, especially if the person holds their breath, tenses their
muscles or flexes their knees too tightly against their chest.
Diagnostic analysis of changes in fluid pressure during lumbar
puncture procedures requires both attention to the patient's condition
during the procedure and to their medical history.
- Increases in CSF pressure after withdrawal of fluid can indicate
congestive heart failure, cerebral edema, subarachnoid hemmorage, hypo
osmolalty resulting from hemodialysis, meningeal inflamation, purulant
meningitis or tuburculous meningitis.
- Decreases in CSF pressure can indicate complete subarachnoid blockage,
leakage of spinal fluid, severe dehydration, hyperosmolality, or
circulatory collapse. Significant changes in pressure during the
procedure can indicate tumors or spinal blockage resulting in a large
pool of CSF, or hydrocephalous associated with large volumes of CSF.
- The presence of white blood cells in cerebrospinal fluid is called
pleocytosis. Counts above 500 usually indicate a purulant infection.
Usually present as granulocytes, white cells can also indicate
reaction to repeated lumbar punctures, reaction to a needle
contaminated with detergent, reactions to prior injections of
medicines or dies, central nervous system hemorrhage, leukemia or a
- Several substances found in cerebrospinal fluid are available for
- Measurement of chloride levels can detect the presence of tuberculous
- Decreased glucose levels can indicate fungal, tuburculous or pyogenic
infections, lymphomas, leukemia spreading to the meninges,
meningoencepalatic mumps or hypoglycemia.
- Increased glucose levels in the fluid can indicate diabetes.
- Inreased levels of glutamine are often involved with hepatic
encephalopathies, Reye's syndrome, hepatic coma, cirrhosis and
- Increased levels of lactate can occur the presence of cancer of the
CNS, multiple sclerosis, low blood pressure, low serum phosphorus,
respiratory alkalosis, idiopathic seizures, traumatic brain injury,
cerebral ischemia, brain abscess, hydrocephalus, hypocapnia or
The enzyme lactate dehydrogenase can be measured to assess meningial
infections as being of bacterial origin, which are often associated
with high levels of the enzyme, or in the absence of unusual levels as
likely being of viral origin.
- Changes in protein content of cerebrospinal fluid can result from
pathogically increased permeability of the blood-cerebrospinal fluid
barrier, obstructions of CSF circulation, meningitis, syphilis, brain
abscesses, subarachnoid hemorrhage, polio, collagen disease or
Guillian-Barre syndrome, leakage of CSF, increases in intracranial
pressure or hyperthyroidism.
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