Intraoperative Neurophysiological Monitoring (eBook)

General Outline 5
1: Introduction 11
References 14
2: Basis of Intraoperative Neurophysiological Monitoring 18
Introduction 18
Reducing the Risk of Neurological Deficits 19
Techniques for Reducing Postoperative Neurological Deficits 19
Sensory System. 19
Motor Systems. 20
Peripheral Nerves. 20
Interpretation of Neuroelectric Potentials 21
When to Inform the Surgeon 23
False Alarms 24
Nonsurgical Causes of Changes in Recorded Potentials 25
How to Evaluate Neurological Deficits 26
Aiding the Surgeon in the Operation 26
Working in the Operating Room 27
How to Reduce the Risk of Mistakes in Intraoperative Neurophysiological Monitoring 27
Reliability of Intraoperative Neurophysiological Monitoring 28
Electrical Safety and Intraoperative Neurophysiological Monitoring 28
How to Evaluate the Benefits of Intraoperative Neurophysiological Monitoring 29
Assessment of Reduction of Neurological Deficits 29
Which Surgeons Benefit Most from Intraoperative Monitoring? 29
Research Opportunities 30
References 30
3: Generation of Electrical Activity in the Nervous System and Muscles 32
Introduction 32
Unit Responses 34
Near-Field Responses 34
Responses from Nerves 35
Initiation of Nerve Impulses. 35
Natural Stimulation. 35
Electrical Stimulation. 36
Monopolar Recording Compound Action Potentials from a Long Nerve 37
Effects of Temporal Dispersion of Action Potentials. 38
Determining the Number of Active Nerve Fibers. 39
Bipolar Recording from a Nerve 40
Responses from Muscles 42
Responses from Fiber Tracts 43
Response from Nuclei 44
Far-Field Potentials 46
Nerves and Fiber Tracts 47
Nuclei 47
Effect of Insults to NERVES, Fiber Tracts and Nuclei 47
The Injured Nerves 48
The Injured Nuclei 49
References 49
4: Practical Aspects of Recording Evoked Activity from Nerves, Fiber Tracts, and Nuclei 51
Introduction 51
Preparing the Patient for Monitoring 52
Recording and Stimulating Electrodes 53
Earphones 55
Light Stimulators 55
Electrical Stimulation of Nervous Tissue 55
Magnetic Stimulation of Nervous Tissue 56
Display of Results 56
Recording of Near-Field Potentials 56
Recording from Muscles 56
Monitoring the Function of Peripheral Nerves 57
Recordings from Fiber Tracts, Nuclei, and the Cerebral Cortex 57
Recording of Far-Field Potentials 58
Placement of Recording Electrodes 58
Electrical Interference 58
Continuous Electrical Interference 59
Interference that Appears Intermittently During an Operation 59
How to Achieve Optimal Recordings 59
Decrease the Electrical Interference that Reaches the Recording Electrodes 60
Selection of Stimulus and Recording Parameters 60
Optimal Processing of Recorded Responses 60
Optimal Placement of Recording Electrodes 60
Quality Control of Evoked Potentials 60
Reliability of Intraoperative Monitoring 61
References 61
Sec1_Pt2 62
5: Anatomy and Physiology of Sensory Systems 63
Introduction 63
The Somatosensory System 64
Sensory Receptors 64
Ascending Somatosensory Pathways 65
Dorsal Root Fiber Collaterals. 67
Dorsal Column System. 67
Organization of the Somatosensory Cortex. 69
Anterior Lateral System. 70
Anterior and Posterior Spinocerebellar System. 70
The Trigeminal System. 71
Electrical Potentials Generated by the Somatosensory Nervous System 71
Near-Field Evoked Potentials. 72
Far-Field Evoked Potentials. 74
Upper Limb SSEP. 74
Lower Limb SSEP. 75
Neural Generators of the SSEP 76
Upper Limb SSEP. 77
Lower Limb SSEP. 78
The Auditory System 79
The Ear 79
Sound Conduction to the Cochlea. 81
The Cochlea 81
Frequency Analysis in the Cochlea. 81
Sensory Transduction in the Cochlea. 82
Electrical Potentials Generated in the Cochlea. 83
Auditory Nervous System 84
Anatomy 85
Classical (Lemniscal) Pathways. 85
Auditory Cortex. 87
Nonclassical (Extralemniscal) Pathways. 87
Physiology. 87
Frequency Tuning. 87
Tonotopic Organization. 88
Descending Auditory Nervous System 88
Anatomy. 88
Physiology. 88
Electrical Potentials from the Auditory Nervous System 88
Auditory Brainstem Responses. 89
Neural Generators of the ABR. 90
The Visual System 93
The Eye 93
Receptors. 93
Ascending Visual Pathways 94
Visual Evoked Potentials 94
Neural Generators of the VEP. 94
References 95
6: Monitoring Somatosensory Evoked Potentials 99
Introduction 100
SSEP in Monitoring of the Spinal Cord 101
Stimulation 102
Upper Limb SSEP 103
Lower Limb SSEP 104
Which Nerves Should Be Stimulated?. 105
Dermatomal Evoked SSEP 107
Recording SSEP for Monitoring Peripheral Nerves 107
Pedicle Screws 110
Stimulation Technique and Parameters for SSEP Monitoring 110
Peripheral Nerves 110
Optimal Stimulus Rate. 111
Dermatomes 112
Recording of SSEP 112
Optimization of SSEP Recordings. 113
Interpretation of SSEP 115
What Kinds of Changes Are Important? 116
Effect of Temperature and Other Nonpathological Factors 116
Evoked Potentials from the Spinal Cord 117
Spinal Evoked Potentials Elicited by Stimulation of Peripheral Nerves 117
Neurogenic Evoked Potentials. 117
Stimulation Technique and Parameters 117
Combination of SSEP and MEP Monitoring 117
SSEP as an Indicator of Ischemia from Reduced Cerebral Blood Perfusion 120
Basis for the Use of SSEP in Monitoring Cerebral Ischemia 120
Practical Aspects of Recording SSEP for Detecting Ischemia 121
SSEP Compared with Direct Measurement of Blood Flow 122
SSEP as an Indicator of Brainstem Manipulation 122
Pre- and Postoperative Tests 122
Trigeminal Evoked Potentials 123
Anesthesia Requirements for Monitoring Cortical Evoked Potentials 123
Abnormalities and Pathologies that Occur Before the Operation that is to Be Monitored 125
References 125
7: Monitoring Auditory Evoked Potentials 129
Introduction 130
Auditory Brainstem Responses 131
How to Obtain an Interpretable Record in the Shortest Possible Time? 131
Stimulus Intensity. 131
Stimulus Repetition Rate. 131
Sound Delivery. 133
Electrode Placement. 134
Types of Electrodes. 135
Processing of Recorded ABR 136
Filtering of Recorded Potentials. 137
Quality Control. 138
Display of ABR in the Operating Room 138
Recording of Near-Field Potentials 138
Direct Recording from the Eighth Cranial Nerve 138
The Anatomy of CN VIII. 139
Recording from the Vicinity of the Cochlear Nucleus 141
Interpretation of Changes in Auditory Responses 147
Interpretation of Changes in the ABR 147
Interpretations of CAP from CN VIII and the Cochlear Nucleus 147
Recordings from the Cochlear Nucleus 149
Effect of Injury to the Auditory Nerve on the ABR 151
Relationship Between Changes in ABR and in CAP from the Auditory Nerve and the Cochlear Nucleus 152
Other Causes of Injury to the Auditory Nerve 154
Injury to the Auditory Nerve from Irrigating. 154
Unknown Causes of Injury to the Auditory Nerve. 154
Practical Aspects Regarding Monitoring Auditory Evoked Potentials in Operations for Vestibular Schwannoma 155
Recording of ABR 156
Recording from the Vicinity of the Ear 157
Recording CAP Directly from the Exposed Eighth Cranial Nerve 159
Recording from the Vicinity of the Cochlear Nucleus 159
Effect of Drilling of Bone 159
Factors Other than Surgical Manipulation that May Influence Auditory Evoked Potentials 160
Effects of Preoperative Hearing Loss on ABR and CAP from the Auditory Nerve 160
Previous Injuries to CN VIII 161
Relationship Between Auditory Evoked Potentials and Hearing Acuity 161
Other Advantages of Recording Auditory Evoked Potentials Intraoperatively 163
Anesthesia Requirements 164
References 164
8: Monitoring Visual Evoked Potentials 168
Introduction 168
VEP as Indicator of Manipulation of the Optic Nerve and Optic Tract 168
Techniques for Recording VEP 169
Anesthesia Requirements for Visual Evoked Potentials 170
References 170
Sec1_Pt3 171
9: Anatomy and Physiology of Motor Systems 172
Introduction 173
General Organization of the Spinal Motor Systems 173
Motor Cortices 175
Somatotopic Organization. 176
The Organization of the Motor Cortices Is Dynamic. 176
Other Functions of Motor Cortices. 176
Basal Ganglia 177
Anatomical Organization of the Basal Ganglia 178
Dormant and Active Connections 179
The Role of the Basal Ganglia in Motor Control 180
Thalamus 180
Cerebellum 180
Descending Motor Pathways 181
Origin of the Descending Pathways from the Motor Cortices 182
Corticospinal Tract 183
Medial System 184
Pontine Motonuclei. 184
Origin of the Tracts of the Medial System. 185
Nonspecific Descending Systems 185
The Spinal Cord 186
The Importance of Synaptic Efficacy 186
Lower Spinal Motoneuron 188
Segmental Pathways 188
Alpha Motoneurons 189
Spinal Reflexes 189
Blood Supply to the Spinal Cord 191
Arteries 192
Spinal Perfusion Varies Along the Spinal Cord. 195
Individual Variations. 196
Veins 197
Physiology of the Spinal Motor System 198
Descending Activity of the Corticospinal System 198
Recording from the Spinal Cord 198
D and I Waves. 198
Response from Muscles 200
Brainstem Control of Motor Activity 201
Central Control of Muscle Tone and Excitability 201
Spinal Control of Muscle Excitability 202
The Value of Animal Studies 202
Disorders and Abnormalities in Motor Systems 203
Disorders Related to the Basal Ganglia and Their Treatment 203
Stimulation of Structures Other Than the Basal Ganglia for Motor Diseases 205
Organization of Cranial Motor Nerve Systems 205
Cranial Motonuclei 205
References 206
10: Practical Aspects of Monitoring Spinal Motor Systems 209
Introduction 210
Monitoring the Corticospinal System 211
Transcranial Stimulationof the Motor Pathways 211
Transcranial Magnetic Stimulation of the Motor Cortex 212
Transcranial Electrical Stimulationof the Motor Cortex 213
Practical Use of Electrical Stimulation of the Motor Cortex 214
Electrode Placement. 214
Anesthesia 215
Safety Concerns in Transcranial Electrical Stimulation 215
Direct Stimulation of the Motor Cortex 216
Recording of the Responseto Electrical or Magnetic Stimulation 216
Practical Aspects of Recording D and I Waves 217
Interpretation of Recorded Responses 218
Recording of Muscle Evoked Potentials 218
Interpretation of EMG Potentials. 219
Monitoring of the Medial System 220
Stimulation and Recording from the Spinal Cord 220
Monitoring F and H Responses 221
Monitoring During Specific Surgical Procedures 221
Scoliosis Operations and Removal of Spinal Cord Tumors 222
Placement of Pedicle Screwsfor Spinal Fixation 223
Stimulation of Cervical Motor Roots 226
Effects of Anesthesia on Monitoring Spinal Motor Systems 226
Effects on Epidural Responses to Stimulation of the Motor Cortex 226
Effects on EMG Activity 227
Mechanisms of Suppressionof Motor Responsesby Anesthetics 229
How to Overcome Lack of Facilitatory Input to Alpha Motoneurons? 230
Muscle Relaxants 232
References 233
11: Practical Aspects of Monitoring Cranial Motor Nerves 237
Introduction 237
Monitoring of the Facial Nerve 238
Facial Nerve Monitoring in Removal of Vestibular Schwannoma 239
Recording Facial EMG. 240
Identification of the Location of Injury. 244
Identifying the Trigeminal Motor Nerve. 244
Mechanically-Induced Facial Nerve Activity. 245
Heat as a Cause of Injury to the Facial Nerve. 245
Indications for Grafting of the Facial Nerve. 246
Continuous Monitoring of the Function of the Facial Nerve 246
Monitoring the Facial Nerve in Other Operations 248
Monitoring of Other Cranial Motor Nerves 249
Monitoring of Cranial Nerves III, IV, and VI 249
Monitoring Lower Cranial Motor Nerves 251
TMS of Cranial Nerves 254
Monitoring the Extracranial Portion of the Facial Nerve 254
Monitoring Functional Aspects of the Brainstem 255
ABR as an Indicator of Brainstem Manipulations 255
Large Vestibular Schwannoma and Skull Base Tumors 255
Other Advantages of Recording Auditory Evoked Potentials Intraoperatively 258
References 258
Sec1_Pt4 261
12: Anatomy and Physiology of Peripheral Nerves 262
Introduction 262
Anatomy 262
Classification of Peripheral Nerves 262
Sensory Nerves 264
Motor Nerves 264
Pathologies of Nerves 264
Focal Injuries 265
Regeneration of Injured Nerves 266
Signs of Injuries to Nerves 267
Mechanosensitivity of Injured Nerves 267
References 267
13: Practical Aspects of Monitoring Peripheral Nerves 269
Introduction 269
Intraoperative Measurement of Nerve Conduction 269
Recordings of CAP from Peripheral Nerves 270
Other Methods for Assessing Injuries to Peripheral Nerves 270
Identification of the Anatomical Location of Nerve Injuries 270
Assessing Nerve Injuries 270
Localizing the Place of Injury. 271
Determination of Neural Conduction Velocity. 271
References 271
Sec1_Pt5 272
14: Identification of Specific Neural Tissue 273
Introduction 273
Localization of Motor Nerves 274
Localization of Cranial Motor Nerves 274
Practical Aspects of Identification of Motor Nerves. 274
Choice of Stimulation. 275
Technique that Can Facilitate Finding a Nerve that Is Embedded in Tissue. 275
Bipolar Versus Monopolar Stimulating Electrodes. 275
Injured Nerves. 275
Mapping the Course of Peripheral Motor Nerves 276
Safety Concerns 276
Mapping of Sensory Nerves 276
Identifying the Different Branchesof the Trigeminal Nerve 277
Identifying the Auditory and the Vestibular Portions of CN VIII 278
Identifying Spinal Dorsal Rootlets that Carry Specific Sensory Input 279
Mapping of the Spinal Cord 279
Mapping of the Floor of the Fourth Ventricle 281
Requirement of Electrical Stimulation 282
Localization of the Somatosensory and Motor Cortex (Central Sulcus) 282
Anesthesia Requirements 285
Mapping Cortical Areas for Epilepsy Operations 285
Mapping of the Insular Cortex 285
Mapping for Tumor Removal. 286
Mapping of Language Memory Areas 287
References 290
15: Intraoperative Diagnosis and Guidance in an Operation 293
Introduction 293
Diagnosis of Injured Peripheral Nerves 293
Neuroma in Continuity 294
Localizing the Place of Injury 295
Practical Aspects of Intraoperative Diagnosing. 295
Stimulus and Recording Parameters. 297
Identification of the Compressing Vessel in Operations for HFS 298
The Abnormal Muscle Response 298
Use of the Abnormal Muscle Response for Monitoring MVD Operations for HFS. 300
Technique Used to Monitor the Abnormal Muscle Response 304
Physiologic Guidance for the Placement of Stimulating Electrodes and for Making Lesions in the Brain 305
Implantation of Electrodes in the Basal Ganglia and Thalamus 306
Localization of Specific Basal Ganglia Structures in Movement Disorders. 306
Basal Ganglia Targets 307
Responses from Cells in the Basal Ganglia. 307
Equipment for Microelectrode Recordings. 309
Display of Results and Quality Control. 309
Monitoring Implantation of Auditory Prostheses 311
Physiologic Guidance for Placement of ABI 312
Guidance for Placement of Stimulating Electrodes in Other Parts of the CNS 312
Anesthesia Requirements 312
References 313
Sec1_Pt6 316
16: Anesthesia and Its Constraints in Monitoring Motor and Sensory Systems 318
Introduction 318
Anesthesia Agents 319
Inhalation Anesthesia 319
Intravenous Anesthesia 320
Other Drugs 320
Achieving the Goals of Anesthesia 320
Keeping the Patient Unconscious 320
Freedom of Pain 321
Prevent the Patient from Moving 321
Additional Purposes of Drugs Used in Anesthesia 322
Basic Physiology of Agents used in Anesthesia 322
Muscle Relaxants 323
Effects of Anesthesia on Recording Neuroelectrical Potentials 323
Recording of Sensory Evoked Potentials 323
Recording of EMG Potentials 324
References 324
17: General Considerations About Intraoperative Neurophysiology and Monitoring 325
Introduction 325
Mistakes and Errors 327
How Can Mistakes Be Avoided? 327
How to Reduce the Risk of Mistakes? 328
The “KISS” Principle (Keep It Simple and Stupid) of Intraoperative Neurophysiology. 328
Importance of Thinking Ahead. 329
Advantage of Using a Checklist. 329
Unexpected Events. 329
Equipment Malfunction. 330
Absence of Response. 330
Communication Is Important 330
Electrical and Magnetic Interference in the Operating Room 331
Identifying the Sources of Electrical and Magnetic Interference 331
Examining the Operating Room for Sources of Electrical Interference. 332
Examining the operating room for magnetic interference. 333
The Signature of Different Interference Signals 333
How Can Interference Signals Reach Physiological Recording Equipment? 334
Electrical Interference. 334
How to Reduce the Effect of Interference 336
Electrical Interference. 336
Magnetic Interference. 337
Electrical Safety in the Operating Room 338
Patient Safety 338
Safety to Personnel Working in the Operating Room 339
Other Risks from Working in the Operating Room 340
References 340
18: Equipment, Recording Techniques, and Data Analysis and Stimulation 341
Introduction 341
Equipment 342
Requirements of Equipment for Intraoperative Monitoring 343
Amplifiers 344
Common-Mode Rejection. 344
Maximal Output. 344
Low-Pass and High-Pass Filters. 345
Notch Filters (Line Frequency Rejection Filters). 346
Electrical Stimulators 346
Constant-Current Versus Constant-Voltage Stimulation. 346
Output Limitations of Electrical Stimulators. 348
Stimulating Electrodes. 348
Magnetic Stimulation 349
Sound Generators 349
Light Stimulators 350
Audio-Amplifiers and Loudspeakers 350
Computer Systems 350
Display Units. 350
Recording Techniques 351
Recording of Far-Field Evoked Potentials 351
Recording of Near-Field Evoked Potentials from Muscles and Nerves and from the CNS 352
Bipolar or Monopolar Recordings. 352
Signal Processing and Data Analysis 352
Signal Averaging of Evoked Potentials 353
Effect of Periodic Interference Signals. 353
Artifact Rejection. 354
Reducing Effects of Amplifier Blockage. 355
Ways to Optimize Signal Averaging. 356
Averaging Slowly Varying Evoked Potentials. 356
Quality Control of Evoked Potentials. 356
How to Reduce the Effect of Electrical Interference 357
What Is Aliasing and How to Avoid It 358
Filtering of Digitized Signals 361
Filtering in the Time Domain. 362
Practical Use of Digital Filters in Intraoperative Monitoring. 363
More Complex Filtering. 365
Reducing Stimulus Artifacts 367
References 368
19: Evaluating the Benefits of Intraoperative Neurophysiological Monitoring 371
Introduction 371
Reducing the Risk of Postoperative Deficits BY THE USE OF Intraoperative Monitoring 372
Evaluation of Postoperative Neurological Deficits 374
Cost-Benefit Analysis of Reduction in Iatrogenic Injuries Through Monitoring 375
Other Benefits from Neurophysiology in the Operating Room 377
Which Operations Should Be Monitored? 378
Efficacy of Intraoperative Monitoring 379
Consequences of False-Positive and False-Negative Responses 379
Evaluation of Benefits from Electrophysiologic Guidance of the Surgeon in an Operation 380
Benefits from Research in the Operating Room 380
References 380
Appendix 383
Appendix A BRODMANN’S AREAS (SEE FIGS. A.1 AND A.2) 383
Sec2_BM1 383
Appendix B 385
Cranial Nerves: 385
Anatomy and Physiology 385
Functions of the Cranial Nerves 386
CN I. Olfactory Nerve: 386
CN II. Optic Nerve: 386
CN III. Oculomotor Nerve: 386
CN IV. Trochlear Nerve: 386
CN V. Trigeminal Nerve: 386
CN VI. Abducens Nerve: 386
CN VII. Facial Nerve: 386
Nervus Intermedius: 387
CN VIII. Vestibulocochlear Nerve: 387
CN IX. Glossopharyngeal Nerve: 387
CN X. Vagus Nerve: 387
CN XI. Spinal Accessory Nerve: 387
CN XII. Hypoglossal Nerve: 387
b978-0-387-78701_4 390