WI> Excuse me? There is *no* credible evidence that LP causes herniation in a
WI> patient with raised ICP? Are you serious?

Quite.  I actually reviewed the issue, going back to 19th century
articles by Cushing and Dandy, when I published some data a few
years ago about 44 consecutive lumbar punctures in patients with
intracranial mass lesions at our hospital (there were no
complications, and many patients improved).  I included in the
reference list about a half-dozen large series with similar results
(including one series from the Neurological Institute, New York,
with over 400 LPs, including many patients with posterior fossa
masses).

The experimental data is sparse but highly relevant.  The studies
have used either live primates or fresh human cadavers.  Catheters
were placed in the lateral ventricles, cisterna magna, and lumbar
subarachnoid space, with pressure transducers at all sites.
Pantopaque was instilled to follow shifts (if any) of neural tissue.
Artificial CSF was infused into the lateral ventricle to raise the
ICP to 800 mm water.  CSF was then withdrawn from the lumbar
subarachnoid space under *suction* (sort of a mega-LP).  What was
found: no tissue shifts or pressure gradients could be induced.  The
lumbar pressure, not surprisingly, fell to zero immediately.  The
cisternal pressure went from 800 to 0 within 1 second, followed by
the ventricular pressure 1 second later.  None of this should be
surprising to anyone with knowledge of CSF hydrodynamics (or common
sense): fluid flux, like electricity, takes the path of least
resistance, and CSF flows a lot easier than brain tissue.

WI> The phenomenon is known as 'coning', and if you bother to
WI> search the Registrar's database in most places, you will find that there
WI> are deaths caused by compression of the medulla through the foramen magnum

There are also deaths coincident with CT scanning.  We have had many
patients herniate on the CT table or shortly thereafter.  Nobody
blames the CT scan, rather, a patient who is seriously
neurologically ill and deteriorating will likely continue to
deteriorate unrelated to any procedures done.  Anyone who takes care
of critically ill patients, including myself, has had patients who
crashed after LP.  To blame the LP, you need a plausible mechanism
for LP-induced herniation, and there isn't any.

I have one exception to the LP-causes-no-harm rule:  if a patient is
*already* herniating (which is defined hydrodynamically as an
existing pressure gradient between two CSF spaces, which is produced
by a plug of CNS tissue occluding the tentorial hiatus or foramen
magnum), a lumbar tap can cause worsening of the herniation.  In
this circumstance, CSF cannot rapidly flow to equalize pressures,
and tissue "flows" instead.  (This is why an LP or myelogram can
cause worsening in a patient with a spinal mass and complete block.)
Fortunately, the neurologic examination can detect pre-existing
herniation at the tentorium or foramen magnum.  With herniation at
the tentorium, there is pupillary nonreactivity, alteration of the
vestibulo-ocular reflex, Cheyne-Stokes respiration, and stupor or
coma.  With herniation at the foramen magnum, there is quadriplegia.
I recommend that LP be avoided in these settings unless absolutely
necessary.
---

[all else deleted]

I had heard about this article but haven't had time to look it up.
What's the full citation?  This problem shows up on the wards whenever
we suspect memingitis.  I never liked the idea of waiting for the CT
before an LP, especially when it takes an hour at time just to get
the CT started.  I have at time suggested we do the LP first as an old
ID specialist recommended, but have been shot down with dirty looks.
This work is an important reference for internal medicine.

Steve Holland

Many people have died of bacterial meningitis waiting to get
a CT so they could get their LP so they could get treated.

--
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Gordon Banks  N3JXP      | "To the intelligent, life is infinitely mysterious.

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 uabdpo.dpo.uab.edu!gila005 (Stephen Holland) writes:

It is certainly not standard of care to wait for a CT to do an LP
in suspected meningitis.  The usual rule is that if the patient
does not have focal neurological findings and if the fundi look okay,
you proceed immediately to LP.  If you are so concerned about increased
ICP that the LP has to be delayed for a CT, then antibiotics have
to be started prior to the CT (recognizing that this will likely
cause cultures to be negative).

I have seen one patient herniate soon after an LP for meningitis
(where the OP was sky high), but as Jim Zisfein pointed out, it
is hard to know whether this is a post hoc fallacy.
--
David Rind

I'm glad this is now being said.  A number of physicians here are
still of the mind to get a CT first.

Steve Holland

Not in the UK they haven't. If you get to hospital with suspected
meningitis you get one, regardless. There certainly are consultants who try to
get a CT, and if it can be done in 30 minutes or less then OK, but
otherwise we go ahead anyway.

Earlier point about LP and coning: my original point (thanks BTW for the
clarification, Jim) was about patients with severely raised ICP (and I should
have included that word severely! Too used to posting to afu with no rigor...)
I've seen it happen in the Transkei: a chap with persistent headache,
perfectly conscious and coherent, no pupillary dyskinesia, normal respiration,
but with severe papilloedema was given an LP. Within 30 seconds of the needle
being inserted, and samples taken, he was unconcious and Cheyne-Stoking. He
died a couple of minutes later. PM revealed coning. No haemorrhage, or any
other acute cause. He had a large central meningioma. Oh yes, there were no
chronic changes in the medulla, consistent with long-term compression. Draw
your own conclusions...

The point is that while LP is perfectly safe in the vast majority of cases,
there are circumstances where it's inappropriate and very dangerous. Of
course, if the dipstick concerned had acted on the papilloedema (and at least
used a pressure manometer...) it wouldn't have happened.

Later,

The Wisp.

:  uabdpo.dpo.uab.edu!gila005 (Stephen Holland) writes:
: >we suspect memingitis.  I never liked the idea of waiting for the CT
: >before an LP, especially when it takes an hour at time just to get
: >the CT started.  I have at time suggested we do the LP first as an old
: >ID specialist recommended, but have been shot down with dirty looks.
:
: It is certainly not standard of care to wait for a CT to do an LP
: in suspected meningitis.  The usual rule is that if the patient
: does not have focal neurological findings and if the fundi look okay,
: you proceed immediately to LP.  If you are so concerned about increased
: ICP that the LP has to be delayed for a CT, then antibiotics have
: to be started prior to the CT (recognizing that this will likely
: cause cultures to be negative).

Alas, I was specifically taught that one should not perform an LP without a
prior CT, even in a patient without focal neurological findings, because of the
malpractice risk. However, I never delayed beginning antibiotics if I suspected
meningitis; the loss of information from the CSF bacterial culture is small
compared to the risk of damage from unchecked infection. Furthermore, the
{*filter*} cultures will often grow the offending organism, rendering the loss moot.

Brandon Brylawski

:  uabdpo.dpo.uab.edu!gila005 (Stephen Holland) writes:
: >we suspect memingitis.  I never liked the idea of waiting for the CT
: >before an LP, especially when it takes an hour at time just to get
: >the CT started.  I have at time suggested we do the LP first as an old
: >ID specialist recommended, but have been shot down with dirty looks.
:
: It is certainly not standard of care to wait for a CT to do an LP
: in suspected meningitis.  The usual rule is that if the patient
: does not have focal neurological findings and if the fundi look okay,
: you proceed immediately to LP.  If you are so concerned about increased
: ICP that the LP has to be delayed for a CT, then antibiotics have
: to be started prior to the CT (recognizing that this will likely
: cause cultures to be negative).

Alas, I was specifically taught that one should not perform an LP without a
prior CT, even in a patient without focal neurological findings, because of the
malpractice risk. However, I never delayed beginning antibiotics if I suspected
meningitis; the loss of information from the CSF bacterial culture is small
compared to the risk of damage from unchecked infection. Furthermore, the
{*filter*} cultures will often grow the offending organism, rendering the loss moot.

Brandon Brylawski

Thought this might be of interest. Jackie

1. Archer BD.
     Computed tomography before lumbar puncture in acute meningitis: a review
     of the risks and benefits.
   Canadian Medical Association Journal, 1993 Mar 15, 148(6):961-5.
     (UI:  93193033)
     Pub type:  Journal Article; Review; Review Literature.

Abstract: OBJECTIVE: To determine the indications, if any, for routine computed
    tomography (CT) of the brain before lumbar puncture in the management of
    acute meningitis. DATA SOURCES: Original research papers, reviews and
    editorials published in English from 1965 to 1991 were retrieved from
    MEDLINE. The bibliographies of these articles and of numerous standard
    texts were examined for pertinent references. A survey of local
    neurologists was conducted, and legal opinion was sought from the Canadian
    Medical Protective Association. DATA EXTRACTION: There were no studies
    directly assessing the risks of lumbar puncture in meningitis; however, all
    sources were culled for other pertinent information. RESULTS: No cases
    could be found of patients with acute meningitis deteriorating as a result
    of lumbar puncture. The neurologic consensus refuted the need for CT in
    typical acute meningitis. All sources stressed speedy lumbar puncture and
    the early institution of appropriate antibiotic therapy to minimize the
    severity of the illness and the risk of death. CONCLUSIONS: (a) There is no
    evidence to recommend CT of the brain before lumbar puncture in acute
    meningitis unless the patient shows atypical features, (b) for patients
    with papilledema the risks associated with lumbar puncture are 10 to 20
    times lower than the risks associated with acute bacterial meningitis
    alone, (c) CT may be necessary if there is no prompt response to therapy
    for meningitis or if complications are suspected, (d) the inability to
    visualize the optic fundi because of cataracts or senile miosis is not an
    indication for CT and (e) there are no Canadian legal precedents suggesting
    liability if physicians fail to perform CT in cases of meningitis.

I hope this isn't being widely taught.  There's no good reason I know of
for routine CT's in this situation, and the Radiology Suite is not
necessarily a good place for a patient with an acute life-threatening
infection even if antibiotics have been started.  I also suspect that
there are patients where the diagnosis is unclear in whom LP would
be delayed while waiting for a CT and in whom antibiotics would also
be held because the diagnosis of meningitis was felt to be fairly
low on the differential (just the sort of patients in whom early
diagnosis might result in excellent outcomes).

Are other physicians routinely obtaining CT's?  Perhaps the practice
in Massachusetts is different from that in other parts of the
country.
--
David Rind

Malpractice consists of:
1. Duty of care
2. Breach of standard of care
3. Causal connection to 4. Damage

If a patients has *no* features of increased ICP on history and physical,
then the standard of care is *not* breached by performing an LP first.
Rather, the standard of care *is* breached by delaying LP and antibiotics.

It's never a bad idea to cover one's glutei, but it's sad that you consider
that to be your primary rationale for sending the patient off to the CT
scanner without diagnosing and treating them.

Joel

I don't get one before tapping unless the patient doesn't look sick
or has papilledema or focal signs which may indicate impending herniation.
Those with focal signs will also need immediate treatment, before scanning.
If there is a CT in the ER, I may even get one on sick patients,
but if not, you are right, the patient needs treatment first and
stabilize before getting an image.  Depends also on how sure you
are they have meningitis and not something else, like subarachnoid bleed
--
----------------------------------------------------------------------------
Gordon Banks  N3JXP      | "To the intelligent, life is infinitely mysterious.

----------------------------------------------------------------------------

Unfortunately, this is a real risk.  These patients are often very sick
and if you tap them without a CT and they die, a lawyer could very
well convince the jury that you killed them by tapping them.  If the
family had refused autopsy and the coroner hadn't insisted on one, you
could be up the creek trying to prove they didn't herniate.
Just another instance of our legal system causing people to get
worse care and more expensive care.

--
----------------------------------------------------------------------------
Gordon Banks  N3JXP      | "To the intelligent, life is infinitely mysterious.

----------------------------------------------------------------------------

Too bad they didn't check for US precedents.  THe Canadian legal system
is much more sane than ours, at least their civil law system is.

--
----------------------------------------------------------------------------
Gordon Banks  N3JXP      | "To the intelligent, life is infinitely mysterious.

----------------------------------------------------------------------------

The standard of care may be local.  If all physicians in a city
routinely obtain CT's before performing LP's, then that standard
of care may be breached by not performing the CT as I understand
it.
--
David Rind