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<jerry>
IXth International Spinal Monitoring Symposium, Rome 2004
Jerry Larson's Impression of the IXth International Spinal Monitoring Symposium,
Rome 2004.
Sorry I couldn't get to it sooner, but I want to share some impressions of the
meeting. It's a very advanced, elite meeting that usually takes place every
three years; most of the previoius meetings have been either in Japan or the
US, but the last one before this was in Buenos Aires. I've never been before.
It's the kind of meeting that you need to go to if you're on the forefront of
development, or if you want to know what's going on up there at the leading
edge.
There's a rumor that the next one is going to be in Amsterdam, which sounds
pretty good. However, that's only a rumor (which I may have even started myself
;-). I don't even know if that's really decided. If this meeting was a sample,
it's a medium-sized meeting, say 100 people, about like the Beth Israel neurophysiology
meetings (which, by the way, there is one coming up in November).
A lot of the usual suspects were there-- Deletis, Vahe Amassian, Francesco Sala,
Yann Pereon, D B MacDonald, Chuck Yingling, Journee and um, not sure of the
name, Kalkland or something like that from the Netherlands, Tamaki from Japan.
I must be starting to catch on; I understood fully half of what Vahe Amassian
had to say! First time I heard him a few years ago I didn't understand a ruddy
thing.
For a long time in the 90's, I always felt that spine cases were very boring;
I counted myself lucky that I got to do a variety of different kinds of craniotomies
and ENT procedures, so I wasn't stuck in a boring spine case every day. One
of the main reasons that spine cases were so boring and unsatisfying in those
days was that the monitoring itself was boring-- boring and not fully adequate
either, consisting almost entirely of sensory evoked potentials, which are a
good way to monitor the dorsal columns, and a reasonable way to monitor for
a global mechanical injury to the spine, but no good either for vascular injuries
to the ventral cord, or for nerve roots. Pedicle screw testing relieved the
boredom, and improved the efficacy of monitoring, to a degree, and the use of
spontaneous and stimulated EMG helped some too when surgeons and anesthesiologists
could be convinced to go along with it, but there was a period of time lasting
several years when I was clear that we need to be doing transcranal MEP, but
I was in no position to do it. Also, a lot of times it was a struggle just to
get enough support from anesthesia to do SSEP.
Finally in the last couple years we've crossed a threshold such that people
in the real world, everyday monitoring professionals, are routinely doing TCeMEP,
and the anesthesia profession is starting to come around; the anesthetic requirements
for myogenic MEP also allow for any kind of SSEP and EMG you want to do, and
with the three modalities (SSEP, EMG including evoked EMG, and MEP) we have
good comprehensive coverage of the cord and nerve roots. We can do MEP with
FDA-approved, commercially available stimulators, and soon there will be a code
to bill for MEP. (I realize there are still many institutions that haven't caught
up yet). So spinal monitoring is a lot more satisfying now, but-- is that it,
or is there anything new and exciting in prospect?
Well, after this meeting, I'm clear that the answer is overwhelmingly yes. You
ain't seen nothin' yet. There are a variety of advanced techniques under development;
different techniques and different interpretive criteria may be called for in
different kinds of cases. There are prospects of being able to say much more
precisely and accurately what's going on intraoperatively and post-operatively,
leading to more genuinely effective interventions and prognostic information.
It's also true that IONM can provide information about the human nervous system
that can't be obtained any other way: you can't do these experiments on people
any other way, and animal models can't always tell you what you want to know
because the human nervous system is unique. It may not just be about the corticospinal
tract before long; we may have much more information about what you really need
in order to ambulate (or in order to use your hands), about mechanisms of spinal
injury, prognosis, rehab, intensive care.
I'll just give some examples of things that are going on: --a lot of people
are working on ways of getting MEP's more easily and reliably, with spatial
facilitation (e.g. stimulating a nerve to potentiate the MEP), temporal facilitation
such as double-train stimulation. --If you consider the whole system involved
in walking and voluntary movement, not just the corticospinal tract, there may
be more complex stimulation parameters we could use--rate effects, habituation,
facilitation-- to test more of the system. --Reflex testing is something that
keeps coming up, not necessarily as an alternative way of monitoring corticospinal
tract, but as a source of more information about the spinal system. --Deletis
now has a technique where he does collision studies on D-waves, as a routine
part of monitoring. I'm not sure I really understand it, but I think the general
idea is something like this: you stimulate the cord directly, caudal to the
surgery, at about the same time you stimulate cortically. If there is fully
preserved corticospinal tract function below the surgery, the same number of
fibers will be stimulated below as above, so that the collision will be complete.
If not--if there is some neuronal loss across the lesion-- then the caudal signal
will not completely cancel the cranial one, and you'll have a measure of the
degree of compromise. If that changes during the case, you could actually say
something about how much you've lost intraoperatively, and how much remains.
--Techniques of monitoring TAAA surgeries are improving, including the idea
of continuing MEP monitoring in the ICU, which is where a lot of the complications
take place. --Of course this is one of my pet peeves, but I get the impression
that there is a growing recognition of the problems with arbitrary criteria
such as 50%amplitude, and more attention being paid to the process of injury
and to what we actually look at in intraoperative interpretation. Somebody,
forget the name--sorry, gave a presentation on how the percentage criterion
has to be different depending on the amount of variability at the time; Chuck
Yingling talked about patterns of myogenic MEP changes during incipient injury
(changes in threshold, complexity, and amplitude prior to complete loss). There
was some controversy about that; I guess we're all supposed to be doing D-waves!
Of course that's not practical for most of us. One of the things I think we
really need to develop is a way to record D-waves without epidural electrodes.
That might require improvements in technology as well as neurophysiological
sophistication, but I don't think it's impossible. Of course a lot of the leading
literature about MEP has to do with D-wave recordings in intramedullary tumors,
and most of us rarely see an intramedullary tumor either. Ideally, we need to
have both kinds of information, D-wave and myogenic, but most of the time that's
not feasible.
It's clear to me that we have a lot of work to do in educating ourselves, and
anesthesia, and above all the surgeons, so that they can figure out how to use
this increasingly sophisticated information, and even modify surgical approaches.
Test occlusions before taking segmental arteries in anterior procedures; nerve
root stimulation; provocative testing in intravascular procedures; dorsal column
and intramedullary mapping; various forms of sacral monitoring and mapping,
all offer ways to improve techniques and outcomes, and they require not just
technical and interpretive skill on our part, and strong anesthetic support,
but increasing sophistication on the part of surgeons.
I've heard of several cases lately, and in fact I had one myself, where the
neurophysiologist reported the information accurately, but the surgeons didn't
respond appropriately, so the opportunity was lost. (Or you could argue that
neurophysiology didn't communicate effectively enough). For instance, suppose
you lose the MEP, and it might be due to anesthesia. What do you tell the surgeon?
What should be done? I'll leave that as as an excercise for the reader, or a
topic of discussion on the list. It's very clear, though, that you can't just
say, "well, it's probably anesthesia" and do nothing about it, and
you can't just keep on operating with a sinking feeling; there has to be some
appropriate response.
So I'm excited; I think we can look forward to a lot of improvements in our
practice, a lot of new techniques and much better understanding of what we're
doing. The big challenge is going to be keeping ourselves and the surgeons up
on the new developments so we can really make a difference.
I talked to some Europeans about education and training and such, and what I
found out is that they have much the same philosophy of training that we have--
that is, no philosophy and no training! People are still learning, or being
trained, on the job, just like here. The difference is that monitoring there
is probably harder to find, and driven much more by MD's rather than by techs
(and PhD's), by insurance, by billing, by liability. As far as I know, there
are just no mobile services/private practices over there; it's all hospital
based, so if techs and nurses and others do have to be trained, you can take
a long time to do it, whereas here, I'm afraid that a lot of people, whether
they're techs or foreign MD's or whatever, get minimal training before being
thrown in.
Behind our efforts, let there be found our efforts, and let the good times roll!
Jerry Larson, D. ABNM
email: jerry@neuromon.com
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