Cerebral Monitoring in the Operating Room and the Intensive Care Unit

207 Pages·1990·29.376 MB·English

by  Prof. Dr. Enno Freye M.D. (auth.)

CEREBRALMONITORING
INTHEOPERATINGROOMANDTHEINTENSIVECAREUNIT
DEVELOPMENTS IN
CRITICALCAREMEDICINE AND ANESTHESIOLOGY
Volume 22
Cerebral Monitoring
in the
Operating Room
and the
Intensive Care Unit
ENNOFREYE, M.D.
DepartmentofVascularSurgeryandRenalTransplantation
HeinrichHeineUniversityofDlIsseldorf
and
DepartmentofCentralDiagnostics,
RheinischeLandes-undHochschulklinikintheUniversityClinicsofEssen
F.R.G.
"~.
Kluwer Academic Publishers
Dordrecht I Boston I London
LibraryofCongressCataloging-in-PublicationData
Freye,E.(Enno)
Cerebralmonitoringintheoperatingroomandtheintensivecareunit/byEnnoFreye.
p. cm. -- (Developmentsincriticalcaremedicineandanaesthesiology:22)
Includesbibliographicalreferences.
ISBN-13:978-94-010-7341-7
1.Electroencephalography.2.Evokedpotentials(Electrophysiology).3.Patientmonitoring.
4.Therapeutics,Surgical.5.Criticalcaremedicine.1.Title.II.Series.
[DNLM: I.CriticalCare.2.Electroencephalography.3.EvokedPotentials.4.IntraoperativeCare.
5.Monitoring,Physiologic.WLISOF893c]
RC386.6.E43F74 1990
616.8'047547--dc20
DNLM/DLC
forLibraryofCongress 89-19791
CIP
ISBN-13:978-94-010-7341-7 e-ISBN-13:978-94-009-1886-3
001: 10.1007/978-94-009-1886-3
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SoftcoverreprintofthehardcoverI8tedition1990
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Contents
Preface IX
1. Introduction
1.1 RationalefortheuseofcerebralmonitoringintheORandtheICU 1
1.2 Whymonitorthebrain 3
1.3 TheneurologicalapproachtoEEGinterpretation 4
2. TheprincipleofEEGrecordingusingcomputerizedpowerspectral
analysis 6
2.1 DifferencewithconventionalEEGrecording 6
2.2 Electrodeplacement 9
2.3 TechnicalrequirementstoobtainareliableEEGsignal(amplifiers,
filters) 9
2.4 Therecordingprocedure 11
2.5 DisplaytechniquesoftheEEG 13
2.6 ArtifactrejectionduringprocessedEEGmeasurement 15
2.7 Signalconductionandconversion 16
3. Set-upofmonitoringtheEEG:Theelectrodemontage 21
4. AnesthesiaandtheEEG 25
4.1 RationalefortheuseoftheEEGinanesthesia 25
4.2 InhalationalagentsandtheireffectontheEEG
(N 0,halothane,enflurane,isoflurane) 26
2
4.3 IntravenousagentsandtheireffectontheEEG
(barbiturates,etomidate,ketamine,opioids,benzodiazepines,
propofol,CO2) 31
5. TheEEGandcerebralischemia 37
5.1 Differentiationbetweenischemiaandanesthetic-inducedEEG
changes 40
VI Contents
5.2 Cerebralmonitoringduringhypothermiaandextracorporeal
circulation(ECC) 42
5.3 EEGmonitoringduringcarotidendarterectomy 43
6. Cerebralmonitoringintheintensivecareunit 47
6.1 Introduction:Representativecasereports 47
6.1.1 Epileptogenicactivity 47
6.1.2 Monitoringinheadtrauma 48
6.1.3 EEGpost-cerebralmalperfusion 49
6.1.4 SedationinanICUsetting 50
6.1.5 EEGpowerspectrapostmitralvalvereplacement 51
6.1.6 EEGpowerspectraandfocalseizures 51
6.1.7 EEGpowerspectraandbenzodiazepineintoxication 53
6.1.8 EEGmeasurementstodifferentiatebetweendrugoverdose
andbrainlesions 55
6.1.9 The 'diagnosticwindow' inlong-termsedation 57
6.2 EEGpowerspectratodifferentiatebetweensevereheadtrauma
anddrugoverdose 57
6.3 Symptomsofirreversiblecessationoffunctionsofthebrain
includingthebrainstem 58
6.4 AvoidingfalseinterpretationofEEGsignal 59
6.4.1 ElectricalinterferenceandtheEEGsignal 60
6.4.2 Artifactsarisingfrom thepatient 61
6.5 EEGpowerspectraduringsleep 62
7. Troubleshooting 64
8. SystemscurrentlyavailableforprocessedEEGrecording 68
8.1 Introduction 68
8.2 DescriptionofunitsusedforEEGpowerspectralanalysisinthe
ORandtheICU 69
9. SensoryEvokedPotentials(SEPs) 84
9.1 Whattheyareandwhattheyoffer 84
9.2 RationalefortheuseofEPsintheORandtheICU 85
9.3 TheclassificationofEPs 86
10. TheprincipleofSomatosensoryEvokedPotentialmonitoring 88
10.1 Electrodetypes 88
10.2 Procedureforlocatingtheexactstimulussite 89
10.3 ThestimulusnecessaryforSEPrecording 90
10.4 Recordingelectrodes 92
10.5 Procedureforheadmeasurementstodetermineelectrodelocation 93
Contents VII
10.6 Accessoryforelectrodeplacementandremoval 95
10.7 Connectionofelectrodeswiththepreamplifier 101
10.8 Troubleshootingtoeliminatehighimpedanceandelectricalnoise 102
10.9 ThedifferentialamplifierforEEGandEPmeasurements 103
11. Optimisingsignal-to-noiseratio 104
ILl Introduction 104
l1.Ll Filteringofnoisewithintherecordingmachine 104
11.1.2 Theprocessofaveraging 105
11.1.3 Thestimulusrate 107
11.1.4 Stimulusrepetitions(sweeps) 107
11.1.5 Theanalysistime 107
11.2 Proceduretolocatetheoptimalstimulussite 108
11.3 Alternatingrecordingandstimulussites 111
12. Evaluatingtheresponseoftheevokedpotential 113
12.1 Mediannerveevokedpotential 113
12.2 Theposteriortibialnerveevokedpotential 116
12.3 Criteriaforabnormalitiesofbothmedianandposteriortibial
evokedpotential 119
13. Theeffectofdrugsontheevokedpotential 122
13.1 ApplicationofSEPmonitoringintheclinicalsetting 123
13.2 RepresentativeexamplesofSEPtracesatdifferentclinical
situations 123
13.3 PostoperativeuseofSEPs 124
14. UseofevokedpotentialsintheICU 130
14.1 Introduction 130
14.2 SEPsinthediagnosisoflesionsintheplexusoftheupper
extremitiesandincervicalrootlesions 135
14.3 UseofSEPmonitoringinheadtrauma,vasculardisease,andbrain
death 141
14.4 PitfallsandpointersforSEPmeasurementintheORandtheICU 144
15. AuditoryEvokedPotentials(AEPs)andBrainstemAuditoryEvoked
Response(BAERorBAEP) 145
15.1 AuditoryEvokedPotentials 145
15.2 ClinicalapplicationsofBAER 146
16. VisualEvokedPotentials(VEPs) 151
VllI Contents
SummaryontheapplicationofintraoperativeEPmonitoring 155
17. ComplicationsthatariseduringEPmonitoring 156
18. SystemsofuseforEPmeasurementsintheORandtheICU 158
19. NewscopesincerebralmonitoringbytopographicmappingofEEG-
powerspectraandEPwaves 178
20. Appendix 182
20.1 Careofelectrodes 182
20.2 SummaryoftheclinicalapplicationsofEPmonitoringintheOR 184
20.3 SummaryoftheclinicalapplicationsofEPmonitoringinthelCU 185
21. Glossary 187
22. Bibliography 188
Indexofsubjects 194
Preface
Inspiteoftoday'sincreasingbodyofknowledgeinregardtocentralnervousfunc
tion and/or the mode of action of centrally active compounds, little is done to
monitor those patients which are at risk ofcerebral lesions eitherin the ORor in
the ICU. Due to the inconsistency of reports regarding the application and the
benefits computerized EEG and/or evoked potential monitoring will bring to the
clinician,physiciansstillarereluctanttogetinvolvedwithatechnique,whichthey
think, will have little or no effect on the outcome of a patients well being.
However, due to the development in computer technology, data acquisition and
comprehension, it now is possible to monitor such a viable organ as the Central
NervousSystem(CNS)onaroutinebasewithoutbeingaspecialistinneurologyor
electroencephalography. Thus, the book is intended to guide the clinician to use
BEGandevokedpotential monitoring ina day to day situation, withoutgoing too
deep into technicaldetails. Asan improvementofcerebralcare is needed, various
representativecases underlinethe interpretationofEEG powerspectraandevoked
potentialchangesinregardtotheunderlying clinicalsituation. Itishopedthat this
bookwillserveas aguidetoanyonewhoconsiderscerebralmonitoringanecessity
in today's patient care. This may be the anesthesiologist, the intensive care
therapist, thenurseanesthetistas wellasthemedical personnelinthelCU setting.
The aim therefore is to give an ideaofwhatcerebral monitoring can do, what its
limitations are, and how to interpretthe data inthelightofthe otherphysiological
variables. Aside from a short description ofthe devices which are on the market,
emphasis is placedupon the technique ofelectrode placement,data interpretation,
and the techniques ofhow to avoid the recording and processingofdata which is
contaminated with electrical noise. In the light ofdata being derived by cerebral
monitoring,thedataderivedfromothermonitoringsystemsplustheclinicalimpres
sion, a diagnosis in regard to cerebral function can be made on more reliable
grounds. Suitableto use as an introductionoras a reference, Cerebralmonitoring
intheORandtheICUpresents
complete coverage of all aspects ofBEG power spectra and evoked potential
monitoring
themajorfeaturesofEEGpowerspectraandevokedpotentialmachineryinclud
ingamplifiers,filters,andmicroprocessors
IX
X Preface
- suggestions for assessing and improving signal quality, reducing noise and
artifactsencounteredduringmonitoringintheORandtheleu
examples of use ofEEG powerspectra and evoked potential monitoring espe
ciallyrelatedtoanestheticagents,coma,headtrauma,andischemicevents.
In addition, coverage of intraoperative monitoring of various evoked potential
modalities withalistoftest parametersoftypical latency andamplitudecriteriais
provided.
As an introduction, recommendations are given for in-depth coverage ofpractical
organizationtoguidethebeginner.
Many thanks toMrs. Karen Schrecker(San Diego,USA) andBorisNeruda, M.D.
(DUsseldorf,FRG),forproofreadingandstylisticcorrections.
DUsseldorfandEssen, 1990 Prof.Dr.EnnoFreye,M.D.