Neurophysiological Monitoring During Intensive Care and Surgery

The principal aim of neurophysiological monitoring is to prevent damage to the nervous system. Achieving this aim places great demands on both personnel and equipment. Monitoring presents challenging practical problems for anaesthetist and neurophysiologist.

Although the information in this book is correct to the best of our knowledge, no one should attempt to carry out any of the techniques described without having undertaken adequate, recognized training, and without consulting up-to-date local, national and international safety regulations, and local, national and international recommendations on good practice.

Contributors, v
Foreword, vii
Preface, ix
Dedication, x
Acknowledgements, x
Abbreviations, xi
1 The why and the how of neurophysiological monitoring in the ICU and surgery, 1
Introduction, 1
Applications of clinical neurophysiology in the ICU, 1
Monitoring during surgical operations, 3
Assessment of results, 7
Statistical significance of changes, 7
Clinical significance of changes, 8
Confidence intervals, 10
Determining the optimal cut-off point, 11
Comparing two methods of monitoring, 11
The effect of corrective action, 12
Is the risk eliminated by monitoring?, 13
References, 14
2 Neurophysiological instrumentation, connection with patients and recording methods, 17
Introduction, 17
Recording the electrical activities of the nervous system, 18
Electrodes for neurophysiological recording, 18
Electrode placement systems, 24
Connecting electrodes to amplifiers and the recording convention, 29
Amplifiers, 32
Signal bandwidth and filters, 35
Digital systems, 37
EEG recording equipment, 38
General features of EEG machines, 38
Input circuits for EEG recording, 39
Amplifiers for EEG recording, 39
Filters for EEG recording, 40
Analogue EEG systems, 40
Digital EEG systems, 42
Evoked potential recording systems, 48
Electrodes for EP recording, 48
Amplifiers for EP recording, 48
Filters for EP recording, 48
Averaging, 48
EP display, 49
Calibration of EP recorders, 49
EP stimulators, 49
EMG and nerve conduction studies, 53
Electrodes for EMG and nerve conduction studies, 53
Amplifiers for EMG and nerve conduction, 54
Displaying EMG and nerve conduction data, 55
Stimulation for nerve conduction studies, 55
Practical aspects of intraoperative and ICU neurophysiological recording, 55
Safety during neurophysiological recording in the ICU and operating theatres, 55
Intraoperative and ICU EEG recording, 59
Intraoperative and ICU EP recording, 65
EMG and nerve conduction studies, 68
References, 68
3 Introduction to methods for continuous EEG and evoked potential monitoring, 73
Introduction, 73
EEG monitoring, 73
Historical development of EEG monitors, 73
Technical requirements for EEG monitoring in the ICU and during surgical operations, 85
Evoked potential monitoring, 94
Technical requirements for EP monitoring, 94
Comparisons between currently used methods, 100
Conclusions, 102
References, 103. 4 Normal and pathological phenomena in EEG, evoked potential, EMG and nerve conduction studies, 109
General introduction, 109
EEG WAVEFORMS AND INTERPRETATION, 109
Introduction, 109
Describing EEG phenomena, 109
Wave shape (morphology), 110
Rhythmicity, 110
Frequency of repetition, 110
Amplitude, 110
Transients, 112
Spatial distribution, 113
Spatiotemporal patterns, 113
Symmetry and synchrony, 113
Inherent variability of the EEG and other biological rhythms, 113
Reactivity, 114
General categories of abnormality in the EEG of importance for ICU and intraoperative monitoring, 114
Change in frequency content, 114
Amplitude reduction, 115
Localized and lateralized abnormalities, 116
Rhythms at a distance (projected rhythms), 117
Altered reactivity, 118
Epileptiform activity, 119
Periodicity, 120
Burst suppression pattern, 123
Electrocerebral inactivity - electrocerebral silence (ECS) - the isoelectric EEG, 124
EVOKED POTENTIAL WAVEFORMS AND INTERPRETATION, 125
General definition - limitations - clinical utility of evoked potentials, 125
Responses and EP components, 126
The electroretinogram and electrocochleogram, 126
Relation between neuronal responses and surface evoked potentials, 127
Action potentials, 127
Postsynaptic potentials, 128
Near-field versus far-field evoked potentials, 128
How to localize evoked potential sources from surface recordings, 130
Normal findings by modality, 131
Flash VEPs, 131
Auditory evoked potentials: BAEPs and MLAEPs, 132
Somatosensory evoked potentials, 134
EMG FINDINGS AND INTERPRETATION, 145
Features of motor units recorded by needle electrodes, 145
Other normal EEG phenomena, 145
Insertion activity, 145
End-plate noise, 145
Fibrillations at single sites, 146
Fasciculations, 146
Nerve conduction, 147
Effects of limb temperature on nerve conduction, 147
References, 148
5 Neurophysiological monitoring during sedation and anaesthesia, 155
Introduction, 155
Sedation: assessment with EEG and evoked potentials, 155
Effects of sedative drugs on the EEG, 155
Effects of sedative drugs on EPs, 157
Assessment of sedation, 159
Anaesthesia: assessment with EEG and evoked potentials, 161
Effect of anaesthetic agents on the EEG, 161
Effect of anaesthetic agents on EPs, 172
Combined EEG and evoked potential measures, 176
Awareness during anaesthesia, 176
Neurophysiological features useful in prediction of possible awareness during anaesthesia, 177
Medico-legal aspects of awareness during anaesthesia, 180
References, 182
6 Neurophysiological work in the ICU, 189
Introduction, 189
Neurophysiological parameters to be monitored and procedures, 189
Sleep in the ICU, 189
CLINICAL CONDITIONS AFFECTING THE CENTRAL NERVOUS SYSTEM ENCOUNTERED IN ICU, 189
Coma and related states, 189
EEG recording and interpretation in coma and related states, 189
EPs in comatose patients, 199
EPs combined with other variables, 215
Cardiac arrest and hypoxic - ischaemic encephalopathies, 216
Other metabolic and toxic encephalopathies and multiple organ failure, 218
Encephalitis, 218
Epileptiform discharges and status epilepticus, 218
Head injury and other neurosurgical applications, 221. Vegetative states and brainstem death (brain death), 225
Vegetative states, 225
Brainstem death (brain death), 228
CLINICAL CONDITIONS AFFECTING THE PERIPHERAL NERVOUS SYSTEM AND MUSCLES ENCOUNTERED IN THE ICU, 231
Neuromuscular syndromes of critical illness (critical illness neuropathy), 231
Acute onset neuropathies, 234
Guillain - Barre syndrome (GBS), 234
Acute intermittent porphyria, 237
Other causes of acute or subacute peripheral neuropathy, 242
Acute weakness due to disorders of neuromuscular transmission, 242
Botulism, 242
Myasthenia gravis, 242
Familial periodic paralysis and the channelopathies, 242
Non-peripheral causes of acute onset generalized weakness, 243
References, 243
7 Neurophysiological monitoring during surgical operations, 253
Introduction, 253
Intracranial surgery, 253
EEG monitoring in intracranial surgery, 253
Visual evoked potential monitoring, 256
SEP monitoring in intracranial surgery, 257
Posterior fossa surgery, 260
Spinal cord function monitoring, 268
Experimental studies and mechanisms of spinal cord damage, 268
Methods of monitoring cord function, 269
Practical aspects of spinal cord monitoring, 272
Clinical applications of spinal cord monitoring, 274
Spinal root surgery and peripheral nerve surgery, 278
Cerebral ischaemia during non-intracranial surgery, 279
Cardiac surgery, 279
Carotid endarterectomy, 285
References, 292
8 Further signal analysis, 309
Introduction, 309
Data acquisition, 311
Technology, 311
Safety issues, 315
Improving signal quality, 317
Filtering methods, 318
Artefact detection and rejection methods, 327
Signal processing and interpretation, 327
Common processing tasks, 329
Processing methods, 332
Integration of features into the clinical context - pattern classification, 346
Statistical process control, 354
Use of the tools, 358
Decision assistance, 358
Development and uptake of methods, 359
Performance assessment, 359
Display of results, 360
Use of IT facilities, 363
References, 365
9 Legal implications of neurophysiological monitoring, 371
Safety of patients and staff, 371
Electromedical equipment, 372
Infection control, 373
Drugs, 373
Identification of patients and consent to procedures, 373
Inherent risk of procedures, 374
Responsibilities in training and supervising staff, 374
Responsibilities in respect of reports on investigations, 375
References, 375
Index, 377.