Bacterial meningitis has a mortality rate of > 90 percent if untreated and
accounts for nearly 2000 deaths per year in the United States. The goal is to recognize
meningitis and begin empirical treatment promptly. In classic and fulminant cases, about
25 percent, there is little diagnostic challenge; the patient presents with rapid onset of
fever, headache, stiff neck, photophobia, and altered mental status. Seizures occur in 25
percent. It is often not possible to distinguish the various etiologies of meningitis by
clinical or CSF analysis. Mortality is approximately 25 percent in adults. Long term
complications include cognitive defects, epilepsy, hydrocephalus, and hearing loss
occurring in about 25 percent of survivors.
Bacterial meningitis begins with the entry of organisms in to the subarachnoid
space. Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis
dominate as the cause in adults. Their ability to invade through the nasopharynx, survive
blood borne dissemination, and trigger inflammatory processes in the CSF that contribute
to the subsequent pathophysiology is in part related to their being encapsulated. Neural
structures are inflamed leading to cephalgia while swelling of the meninges, accumulation
of CSF, cerebral vessel swelling and brain swelling leads to increased CSF pressure and
Military barracks and college dormitories are typical environments where cases due
to N. meningitidis occur. Conditions that alter immune status such as surgical
splenectomy, steroid therapy or HIV disease should be sought. Recent exposure to
antibiotics may influence the clinical course and CSF interpretation. Neurologic
examination should seek out focality that may be present in 25 percent of cases as well as
for papilledema. Brudzinski sign (flexion of hips with passive neck flexion) and
Kernigs sign (contraction of hamstrings with knee extension with hip flexed) occur
in 80 percent. An exam of the skin for purpura, petechiae, maculopapular rash, and signs
of microembolization should be sought.
Immediate lumbar puncture (LP) is the only way to confirm the diagnosis and
identify the organism. It is unnecessary and inexcusable to delay the LP for any other
procedure such as an imaging study. The spinal fluid in bacterial meningitis is milky
colored, and has thousands of polymorphonuclear leukocytes (PMNs). The CSF protein will be
several hundred to more than a thousand mg/100ml (normal <4.0), and the CSF glucose
below 50 (normal ~100). In very early bacterial meningitis there may only be a few hundred
PMN, and moderately elevated protein, but the glucose will be depressed. With a
presumptive diagnosis of bacterial meningitis, awaiting the results of gram stain,
ceftriaxone 1 gram IV can be administered for coverage of the most common organisms. If
the patient has seizures, these should be treated with phenytoin, 15 mg/kg over the first
2 hours, and then 300-500 mg/day depending on the patient's size and blood concentrations,
if available. Timely consultation is very important. Once stabilized, arrangements should
be made for transfer of the patient for further definitive care.
When the patient has clinical signs of meningitis, but the spinal fluid has fewer than
500 WBC, predominantly lymphocytes, protein below 200, and normal CSF glucose, the gram
stain will seldom show any bacteria. This is usually called aseptic meningitis, because of
the absence of bacteria. Cultures still need to be taken in the event the patient has
compromised reaction or the infection is still early. Antibiotics should usually not be
initiated unless there is other evidence to suggest a bacterial infection.
When suspecting aseptic meningitis, depending upon the setting, skin tests for TB, a
chest x-ray, a reagin test for
syphilis, fungal cultures, and India ink preparations
should be done. Viruses are the most common cause of this picture in military age groups.
Viral meningitis, usually caused by enteric viruses, tends to occur in local epidemics
in the late summer and runs a course lasting about 10 days to 2 weeks. Treatment consists
of supportive care, analgesics, hydration, and enteric isolation. Preventive medicine
technicians should look for spread of illness and pay particular attention to latrines,
food service, and berthing areas.
Partially Treated Meningitis
Unfortunately, this is all too common a scenario: a patient has been recently
treated with an antibiotic or sulfa drug for some minor condition and now returns for
medical care because of systemic symptoms to include a headache, nausea, vomiting,
photophobia, and stiff neck. The spinal fluid shows a few hundred lymphocytes, moderate
elevation of protein, a negative gram stain, and negative cultures. Does the patient
simply have viral meningitis, or does he or she have bacterial meningitis obscured but not
adequately treated with antibiotics? If there is a major medical treatment facility
nearby, this patient must be transferred for evaluation and treatment. If there is
currently an epidemic of typical viral meningitis at the command or in the community, it
is reasonable to discontinue the patients antibiotics, examine the patient every day
and repeat their LP in 1 or 2 days for signs of infection. If the patient cannot be
quickly referred to a treatment facility and if there is not a local outbreak of viral
meningitis to account for the patients illness, the GMO must contact an infectious
disease specialist for consultation and start the patient on high doses of
penicillin for 2 weeks.
The Lumbar Puncture
Spinal fluid is the only source to identify the organisms in meningitis, so a lumbar
puncture must be done for the diagnosis. Spinal fluid is also necessary for some viral
studies, chemical studies in some degenerative diseases, cytologic studies in lymphoma and
leukemia, diagnosis of Guillain-Barre syndrome, adjunctive data in the diagnosis of
multiple sclerosis, and therapeutic relief of pressure in benign intracranial
hypertension, and some forms of hydrocephalus.
The sterile tray and collection tubes should be ready and the manometer and stopcock
assembled before the patient is touched. Assemble all equipment out of the view of the
patient. Standard aseptic technique requires the use of surgical gloves, mask and safety
glasses, sterile scrub of the patient's back and a suitable drape with an aperture about
15 to 20 cm in diameter for the procedure. The patient should lie on his or her left side
for a right-handed operator, on the right side for a left-handed operator. A firm surface
is important to avoid sagging of the spine, which may make it more difficult to reach the
subarachnoid space. With the patient's neck and knees bent to flex the lumbar spine, the
operator should palpate the interspace between the fourth and fifth lumbar vertebrae, and
hold the tips of his or her left index and middle finger on either side of the interspace.
The patient's back should be perfectly vertical.
Many operators use a local anesthetic such as lidocaine to numb the skin before placing
the needle. Others, however, including this author, find that the use of anesthetic on the
skin does not spare the total amount of discomfort for the patient, but it does prolong
the procedure. With the needle absolutely parallel to the floor, and the bevel facing up,
the needle is gripped at the hub and the tip of the needle is firmly inserted into the
interspinal space between L4 and L5, and directed toward the patient's chin. Proceeding
deliberately but not timidly, the needle should be advanced at least 3 cm before slowing.
When the needle perforates the meningeal sac, there is a detectable soft pop. At this
point the trochar is removed and fluid will dribble out of the needle.
The pressure should not be recorded until the patient stretches back out and relaxes.
Increased abdominal pressure from the flexed posture and groaning will give a misleading
elevated pressure. The normal pressure is less than 200 mm. If the patient appears
agitated or is sobbing, the pressure should not be recorded until the patient is as
relaxed as possible in the situation. After the pressure is recorded, the manometer can be
put aside, a closing pressure provides no useful information.
The first tube of fluid is the least contaminated and it is from this tube that gram
stain and cultures should come. The last tube should have the fewest red cells from the
insertion of the needle, so it should be the one used for cell counts and cytology if
desired. CSF protein and glucose should be measured from a middle tube. It is seldom
necessary to take more than 6-10 cc.
If the needle strikes bone within the first few centimeters, it should first be directed
more toward the head, and if that fails then very slightly more caudad. Once the pop is
encountered if no fluid comes out of the needle, it should be very slowly retracted with
trochar out while rotating it gently. As it is pulled away from the anterior rim of the
space, fluid will emerge.
If fluid cannot be obtained despite these measures, the operator should go the next
interspinal space, L3-L4.
The Difficult LP: Recommendations
If after three attempts, you cannot reach the subarachnoid space, it is best to stop
and ask another colleague to try. The most skillful at this task in most clinics or
hospitals are the anesthetists and anesthesiologists, then the neurologists and
neurosurgeons. Here are a few tricks to try if it is difficult to reach the spinal fluid.
Aseptic technique still is required while following these steps.
Perform the procedure with the patient sitting and hunched forward at the shoulders.
The landmarks are more easily seen in this position, and it is easier to direct the
needle at the midline. Once the needle is inserted, leave it in place and lay the patient
again in a lateral position to measure the pressure.
Use an 18-gauge needle. Most kits now come equipped with a standard 20-gauge needle. The
larger needle is firmer and allows fluid to egress more easily.
Consider sedation with a short acting benzodiazepine such as midazolam to relax the
patient and ease muscle guarding.
Measure the pressure after the patient has settled down - and do not forget to record
it! If the puncture was done in the sitting position, and you cannot lay the person back
on his/her side, then record the pressure from the level of the base of the skull.
Use the first tube for cultures. It will be the least contaminated.
If there is blood in the sample, spin one of the tubes in a centrifuge. If the blood is
caused by your efforts, the supernatant fluid will be clear. If the supernatant fluid is
blood-tinged, that indicates hemolysis, suggesting the cells have been in the fluid for at
least 30 minutes.
Check the cell count (preferably review the slides yourself along with the lab tech).
Check the protein and glucose.
Freeze some fluid immediately, in the event you later determine a need for an additional
Reviewed by CDR Siefert, MC, USN, Emergency Medicine Department, Naval Medical
Center San Diego, San Diego, CA. (1999).