Neural Monitoring: The Prevention of Intraoperative Injury

318 Pages·1990·6.37 MB·English

by  Jun Kimura M. D. (auth.), Steven K. Salzman (eds.)

Neural Monitoring
Neurotrauma
Neural Monitoring: The Prevention of Intraoperative Injury,
edited by Steven K. Salzman, 1990
Neural Monitoring
The Prevention of Intraoperative Injury
Edited by
Steven K. Salzman
Spinal Trauma Research Program
Alfred 1. duPont Institute of the Nemours Foundation
Wilmington, DE
Assisted by
Shirley J. Smith
~
Springer Science+Business Media, LLC
~
LibralY of Congress Cataloging-in-Publication Data
Neural monitoring: the prevention of intraoperative injury / edited
by Steven K. Salzman; assisted by Shirley J. Smith.
p. an. - <Neurotrauma)
"From the proceedings of a symposium held at the Alfred 1. duPont
Institute, September 26 and 27, 1988"-T.p. verso.
Includes index.
ISBN 978-1-4612-6786-7 ISBN 978-1-4612-0491-6 (eBook)
DOI 10.1007/978-1-4612-0491-6
1. Spinal cord-Surgery -Complications and sequelae-Prevention
-Congresses. 2. Spinal cord-Wounds and injuries-Diagnosis-
-Congresses. 3. Somatosensory evoked potentials-Congresses.
4. Patient monitoring-Congresses. 1. Salzman, Steven K.
II. Smith, Shirley J. (Shirley Jean), 1964- . III. Series:
Neurotrauma (Clifton, N.J.)
[DNLM: 1. Evoked Potentials, Somatosensory-physiology
-congresses. 2. Intraoperative Complications-prevention &: control-
-congresses. 3. Monitoring, Physiologic-methods-congresses.
4. Spinal Cord Injuries-prevention &: control-<angresses. WL 400
N4936 1988)
RD594.3.N48 1990
617.4' 8201-dc20
DNLM/DLC
for Ubrary of Congress
90-4625
rev. ap
e 1990 Springer Sc:ience+Busioess Media New Ymk
Originally pubIished by Humana Plas Inc. in 1990
Softcover reprint of the 1wdcover lat edition 1990
AlI rights of any nature reserved.
No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by
any means, electronic, mechanical, photocopying, microfilming, recording, computer database entry,
or networking, or in any manner whatsoever without written permission from the Publisher.
From the proceedings of a symposium held atthe Alfred 1. duPont Institute, September 26 and
27,1988.
Supported by the Nemours Foundation, with additional fund ing provided by Marion
Laboratories;The TECA Corporation; Nicolet Instrument Co.; Axon Systems, Inc.; and Nihon
Kohden America, lnc.
Foreword and
Overview
Although the incidence of acute spinal cord injury is relatively low
(about 40 per million; Brachenetal., 1981), such an injury, which often
results in serious loss of motor and sensory function, is one of the most
catastrophic of medical conditions and has an enormous emotional,
social, and economicimpact on family, community, and society. In the
present volume, recent developments in the prevention and treatment
of spinal cord injury are related. These studies concern the use of so
matosensory-evoked potentials (SEPs) and motor-evoked potentials
as well as treatment of spinal cord injury.
Scalp-recorded cerebral SEPs to stimulation of lower limb nerves
have been studied in many patients with spinal cord injury and have
been used to monitor spinal surgery. Although these responses have
proved useful in providing information concerning the physiological
integrity of spinal cord afferent pathways in these patients, the tech
nique has limitations. Thus, during surgical monitoring, careful atten
tion must be paid to the effect of anesthetic agents and blood pressure
variations that may cause spurious changes in the amplitude or
waveform of the cerebral SEP, which can mimic or obscure deteriora
tion from impaired sensory pathway conduction. These responses are
also subjected to electrical (60-cyde) interference. Even under favor
able and stable anesthetic conditions, the monitoring of SEPs provides
a slow rate of feedback information since at least 100 responses are
averaged at stimulus rates at or less than three per second. Addition
ally, in both surgical monitoring and evaluation of spinal-cord-in
jured patients, cerebral SEP abnormalities reflect dysfunction that is
largely limited to posterior column sensory pathways neither con
cerned with pain or temperature nor uniquely subserving joint posi
tion or vibration sense.
Spinal cord SEPs, which are recorded by inserting electrodes into
,the dorsal epidural space, are also commonly used in surgical moni-
v
vi Foreword and Overview
toring. These are relatively unaffected by electrical interference, or by
usual variations in blood pressure and anesthetic level. They provide
a fast rate of feedback information, since their amplitudes are similar
to cerebral SEPs and their latencies are not affected by rapid rates of
stimulation (up to 20 per second). This response is mediated by mul
tiple spinal cord afferent pathways, and abnormalities are, therefore,
not limited to disturbances in function affecting a single sensory path
way, such as the dorsal columns. Whether this technique is unaccepta
bly invasive must be considered, but there have been no reports of
neurological complications.
Also discussed in this volume is the new technique of recording
motor-evoked potentials. Using this technique an electrical stimulus
is delivered to the motor cortex and underlying white matter by direct
electrical (anodal) stimulation of the scalp or by a magnetic coil placed
over the scalp. The latter technique is painless, which is advantageous
when patients are not anesthetized. Motor-evoked potentials can be
recorded invasively from the spinal cord during surgical procedures
or noninvasively from limb musculature. The interpretation of data
using this technique is more complex than when performing routine
peripheral nerve conduction studies (Cracco, 1987). Nevertheless, un
like the recording of SEPs, this method permits an assessment of the
functional integrity of descending central motor pathways, which are
those most commonly affected in spinal-cord injury induced either by
trauma or during surgery, and which usually result in the greatest
disability. Although much remains to be learned in terms of evalu
ating the clinical utility of this method, enough data is already avail
able to suggest that the method will be of considerable importance in
both the surgical monitoring and the routine evaluation of spinal
cord-injured patients.
Finally, insights into the treatment of spinal cord injury are de
scribed in this monograph. There are many pressing issues. For exam
ple, how much tissue damage in spinal injury is caused by mechanical
disruption of cells and how much by progressive and secondary
injury initiated by the trauma? Posttraumatic ischemia is a strong pos
sible cause of progressive and secondary injury. The improved recov
ery of function in experimental studies of naloxone, which improves
spinal-cord blood flow, supports this interpretation. The efficacy of
steroids in such studies may be in stabilizing membranes after both
primary and secondary injuries. Both steroids and naloxone have
Foreword and Overview vii
antioxidant activity. Calcium-channel blockers may be useful, but are
still in a preliminary phase of study. It is important to emphasize,
however, that such data coming from animal experimentation must
be critically analyzed, because there are many different models with
different experimental treatment outcomes. These studies often lack
objective, quantitative measures of clinical recovery. This is particu
larly important because of difficulties involved in assessing func
tionalloss and recovery by determining the number ofaxons surviv
ing and passing through the injury site. The relationship between
morphology and function is not always clear, since good functional
recovery and relatively normal SEPs are sometimes obtained with
few surviving axons (Blight and Young, this volume).
The very successful symposium on which this monograph is based
was supported by and held at the Alfred I. duPont Institute of the
Nemours Foundation in Wilmington, Delaware on September 26 and
27,1988.
Roger Q. Cracco, MD
References
1. Brachen, M.D., Freeman, D.H., Hellenbrand, K.: Incidence of acute trauma
tized spinal cord injury in the United States, 1970-1977. Am. J. Epidenniol. 113:
615-622,1981.
2. Cracco, R.Q.: Evaluation of conduction in central motor pathways: Tech
niques, pathophysiology, and clinical interpretation. Neurosurgery 20(1):
199-203,1987.
Acknowledgments
I wish to express my gratitude to the Nemours Foundation for its
continued support of biomedical research, and for funding this mono
graph and the symposium on which it is based. I also thank Charles
R. Hartzell, Research Manager, and W. Jeff Wadsworth, General
Manager, of the Nemours Foundation for establishing the framework
that made this effort possible. The excellent photographic skills and
tireless efforts provided by Cindy Brodoway are also gratefully ac
knowledged. Finally, special recognition goes to Shirley J. Smith,
whose contribution went far beyond her secretarial role. Shirley not
only provided editorial assistance, but also was entirely responsible
for the formatting, layout, and initial printing of this volume. She
learned these new skills on the fly, without causing any delays, and
without compromising her usual superior performance for her many
other duties. This book is dedicated to her efforts.
Steven K. Salzman
viii
Preface
The symposium from which this book originates represents a sig
nificant watershed in the field of intraoperative neural monitoring,
since the participants concluded that electrophysiologic monitoring
techniques should be considered a "standard of care" for surgical pro
cedures that place the central nervous system (CNS) at risk for injury.
Specifically, it was agreed that the somatosensory-evoked potential
(SEP) is a remarkably reliable and sensitive indicator of several aspects
of CNS function, and should be routinely employed as an intraopera
tive monitor during many neurosurgical and orthopedic procedures.
The significance of this conclusion cannot be overstated, for at the
time of this writing, intraoperative monitoring methods based on
evoked-potential analyses are still considered experimental and are
not in routine use. The reasons for this are not clear, given the accu
mulation of literature and expertise on this subject over the past five
years. Granted, the cost of electrophysiological monitoring equip
ment is high, but only initially. The benefits of injury prevention far
outweigh these costs, from both medical and economic viewpoints. It
is our sincere hope and goal that the medical community be made
aware of the value of intraoperative neural monitoring.
The participants agreed that the SEP still constitutes the best overall
response for monitoring purposes, but it was recognized that this
method can be prone to technical difficulties, and, at least in theory,
false results. Specifically, it was conceded that selective motor dam
age could occur intraoperatively and that this damage would not be
detected while monitoring sensory system function. The conclusion
was reached, therefore, that the development of motor-evoked po
tential (MEP) monitoring techniques should be continued, and even
tually incorporated with SEPs into a comprehensive monitoring
strategy.
The combined use of SEPs and MEPs should satisfy most of the
theoretical objections to the value of electrophysiological monitoring
techniques, but does not address the very real and pervasive problem
ix
x Preface
of technical error. In spite of the high quality of today's equipment,
the electrically noisy and hostile operating room environment often
limits, or precludes, the ability to record these tenuous and fleeting
electrophysiologic signals. Even when successfully recorded, the via
bility of evoked responses may be misinterpreted because of the lack
of standardized evaluation criteria. Finally, even if a definitely com
promised response is registered, except for cases where instrumenta
tion can be repositioned or removed, the appropriate response to this
warning of impending injury will often remain unclear.
These problems were addressed at this meeting, and several poten
tial solutions were proposed. It was agreed that evoked waveforms
must be evaluated by stricter criteria, and several efforts in this re
gard were presented. Most significantly, it was learned that the patho
chemical response of nervous tissue to injury constituted a posttrau
matic injury progression that was not only predictable, but in fact,
responsible for the deleterious neurologic consequences of injury.
The significance of this insight is twofold: the biochemical responses
to CNS injury could be used as markers to detect injury, and pharma
cologic reversal of these responses could be used to prevent or treat in
jury. Thus, it was proposed that biochemical monitoring techniques
could be used to supplement evoked potentials for the detection of
injury and that early pharmacologic treatment, or even pretreatment,
could be used to minimize the consequences of an injury.
This latter point is important, since it pertains to operatively in
duced CNS injury. A number of effective drugs have been discovered
for the treatment of experimental neural injury. Clinical applications
for these drugs, however, are limited by the requirement of pretreat
ment or early treatment for their efficacy. This is a severe restriction
for the treatment of the majority of CNS injuries encountered clini
cally; however, it is of no concern for the treatment of operative inju
ry. That is, pharmacologic pretreatment can be initiated prior to a
risky surgery and/ or early treatment can be introduced shortly after
the detection of surgical trauma. Thus, a consensus of participants
concurred that the surgical theater now offers a unique opportunity
for the evaluation of promising experimental approaches for the pre
vention and treatment of CNS injury.
Steven K. Salzman