Biology 202
1999 Final Web Reports
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A Brain Drain

Alicia Zukas

Anthrax, arteriovenous malformation (cerebral), chronic inflammatory, polyneuropathy, dementia due to metabolic causes, encephalitis, epilepsy, febrile seizure (children), generalized tonic-clonic seizure, Guillain-Barre syndrome, hydrocephalus, inhalation anthrax, treatments involving leukemia and neuroblastoma, malignant diseases involving the brain or spinal cord, meningitis, multiple sclerosis, normal pressure hydrocephalus (NPH), pituitary tumor, polio, Reye's syndrome, subarachnoid brain hemorrhage, syphilis, tertiary, etc.

Seems like quite an extensive list, and yet the list goes on to include hundreds of dehabilitating diseases which can affect the central nervous system. One thing that all of these conditions have in common is the potential to be discovered with the evidence from a procedure know as the lumbar puncture (spinal tap or cisternal puncture).

Over spring break, I had the wonderful opportunity to intern with a neurologist. During this time, I viewed the lumbar puncture. As painful and invasive as I had imagined it, it was not. I learned that the lumbar puncture is actually a quite simple and absolutely amazing procedure, much less painful than an intravenous or drawing blood.

There is an exorbidant amount of information which can be obtained from the cerebrospinal fluid. Lumbar punctures are an outpatient procedure, usually performed by a neurologist, pediatrician, or family doctor and lasting only a few minutes. The goal of the tap is to collect and measure the pressure of the cerebro spinal fluid (CSF) which surrounds, cusions, and protects the brain and spinal cord. The CSF is a dense water-like fluid secreted by the brain and "flows through the skull and spine into the subarachnoid space, which is the area internal to the arachnoid membrane" (1). It also carries products from neurosecretions, glucose, proteins, and chemicals in the cells (2).

The procedure is quite simple with a prepackaged kit. (3) The patient usually lays down on her side away from the doctor in a fetal position with her knees to her chest. This is so the cranio-spinal axis is entirely parallel to the bed. If this method is not successful, the patient can also sit upright with her knees to her chest. The method is not usually recommended because of the extra risk of herniation and the CSF pressure cannot be accurately measured. The health care provider starts by finding the puncture area below the second lumbar, usually above or below the fifth lumbar vertebrae because of the larger interspace (1). This area is used because it is below the spinal cord; a sac of spaghetti-like nerves hanging down, much like a horse's tail.

The puncture area is draped and swabbed in a circular fashion, moving outwards with iodine until an area of about 20cm in diameter is covered. This is then repeated over with alcohol, because the iodine in the subarachnoid space can "cause irritative arachnoiditis (1)." (4)

The skin is then anestetized with 1% lidocaine by using a 20 gauge needle on a 5 cc syringe, and positioned as if performing the lumbar puncture. The anestetic syringe is drawn back slowly while injecting about 2cc lidocaine, which might have a burning sensation. The lumbar puncture needle is then inserted into this spot until a pop- the piercing of the membrane of the dura (5). The stylet in the needle is withdrawn to check for CSF flow, the venous plexus was hit if there is any blood returned and the procedure must be redone with a new needle.

I wondered, as I was viewing the procedure, why a syringe didn't just draw the CSF fluid. The pressure of the fluid in the body was enough to force out a sample, so the thin tube-like spinal needle is just placed between the lumbar for collection of the fluid. A syringe is also not used because of the possibility of drawing in and breaking the nerves. Instead, the spinal needle simply passes across the nerves, pushing them to the side, as CSF fluid is drawn.

Once the cerebrospinal fluid is reached, a manometer is attached to the needle to obtain CSF pressure, normal values being between 50 and 180 mm H2O. Usually the flow the about one drop per second, and three to fourth sterile tubes of 1-2 cc specimin are collected. The first is standardly sent for a glucose and protein count, the second for a Gram stain, and culture and sensitivity, the third for cell count and differential. A fourth tube can sometimes be collected for viral tissues or cultures, India ink preparation, Cryptococcus antigen, fungal cultures, VDRL (venereal disease research laboratory test) or cytology (1).

After the collection, the stylet is placed back, and the needle is withdrawn. A simple bandage is placed over the puncture area. The patient should stay in bed for a few more hours and drink liquids to replenish the lost fluid.

Normal pressures of the CSF are between 50 and 180 mm H20, and it normally appears clear and colorless. Increased intracranial pressure may result from trauma or infection. Decreased pressure may indicate "obstruction to the flow of CFS above the puncture site (spinal cord tumor), shock, fainting, or diabetic coma" (1). If the fluid appears cloudy, this could indicate "infection, high white blood cells in the CSF, high protein in the CSF, or microorganisms" (1). If the specimine is brown or orange, this could be high protein or old blood in the sample. CSF normal protein is 15 to 45 mg/100 mL (1). In high protein samples of CSF, this could indicate diabetes mellitus, polyneuritis, tumors, or trauma. Low protein samples shows rapid CSF production. Gamma globulin should be 3 to 12 % of the total protein (1). Increased gamma globulin is usually checked for any demyelinating disease, like multiple sclerosis, neurosyphilis, or Guillain-Barre syndrome.

The blood sugar is usually taken after a lumbar puncture and compared to the glucose level in the CSF. The CSF glucose level should be about 2/3 serum glucose level or 50 to 80 mg/ 100 mL. In high glucose, this is simply high blood sugar, systemic hyperglycemia. In low blood sugar, this is hypoglycemia, bacterial or fungal infection (like meningitis), mumps, or an old subarachnoid hemmorrhage.

The vials of CSF should not contain many white blood cell and no red blood cells. The existance of red blood cells is evidence of internal bleeding traumatic lumbar puncture. Increased white blood cell count shows an acute infection in the central nervous system, active meningitis, beginning of a chronic illness, tumor, abscess, brain infarction, or demyelinating disease.

The venereal disease research laboratory tests are used to screen for syphilis and measures the presence of reagin in serum (6). The cerebrospinal analyzed for fungus is done by complement fixation, "a specific laboratory technique to determine the presence of antibodies formed when an individual has been exposed to an antigen" (7).

"Other tests, like chloride tests, can be done to differentiate disorders that affect the nerves (such as poliomyelitis) from meningeal disorders (like meningitis or tuberculosis)" (1). Chloride should be 110 to 125 mEq per liter (milliequivalent per liter) (1).

When looked at under a microscope, there should be no evidence of bacteria; any bacteria indicates bacterial meningitis or other infections, such as childhood meningitis of the haemophilus influenza organism (8).

The lumbar puncture can also be used to inject dye into the spinal fluid for a myelogram or to inject therapeutic agents (1). They can also allow the injection of pain killers for pain relief.

There are, of course, a few cases in which a spinal tap should not take place. For example, if there was "a prior infection at the site of the puncture, problems with blood clotting, or increased pressure in the head" (1). If the patient has increased intracranial pressue, the puncture could result is death or damage to the spinal cord. Other risks of the lumbar puncture may include "hypersensitivity to the anesthetic, discomfort, headache afterwards, and bleeding into the spinal canal" (1). The post-lumbar puncture headache is the most common side effect, occuring in 15-30% of patients within 24 to 48 hours after dural puncture (9).

While there are alternative methods to collecting spinal fluid, they are not usually recommended. If the patient has a lumbar deformity or prior infection, there is the cisternal punture. This involves "the insertion of a needle below the occipital bone (back of the skull). It can be hazardous because the needle is inserted close to the brain stem" (1). A ventricular puncture is even more rare. This involved collecting the CSF from patients with impending brain herniation and is performed in the operating room. "A hole is drilled in the skull, and a needle is inserted directly into the lateral ventricle of the brain" (1).

Of course the lumbar puncture is not a brain drain. It is actually a virtually harmless procedure, every procedure with its precautions, but less painful then a bee sting. If its is done with a small gauge spinal needle, low CSF pressure and plenty of fluids, the post-lumbar headache can even be avoided. The lumbar puncture procedure is over a hundred years old, and is constanly being perfected and provided more evidence for neurological disorders.

WWW Sources

1)Healthcentral, An excellent comprehensive site for anything pertaining to health.

2)Ask the Mayo Phiysician, an informative question and answer bulletin board.

3)Picture of Lumbar Puncture Tray.

4)Image of Lumbar Puncture

5)Lumbar Puncture Procedures, For med students.

6)Ask the Mayo Physician, More responses from the bulletin board.

7)Healthanswers medical research library.

8)Health central, More information from healthcentral, with image.

9) Medical review., An informative site with lumbar puncture information.




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