Cerebral Monitoring in the Operating Room and the Intensive Care Unit

In spite of today's increasing body of knowledge in regard to central nervous func­ tion and/or the mode of action of centrally active compounds, little is done to monitor those patients which are at risk of cerebral lesions either in the OR or 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, physicians still are reluctant to get involved with a technique, which they 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 Nervous System (CNS) on a routine base without being a specialist in neurology or electroencephalography. Thus, the book is intended to guide the clinician to use BEG and evoked potential monitoring in a day to day situation, without going too deep into technical details. As an improvement of cerebral care is needed, various representative cases underline the interpretation of EEG power spectra and evoked potential changes in regard to the underlying clinical situation. It is hoped that this book will serve as a guide to anyone who considers cerebral monitoring a necessity in today's patient care. This may be the anesthesiologist, the intensive care therapist, the nurse anesthetist as well as the medical personnel in the lCU setting.

1. Introduction.- 1.1 Rationale for the use of cerebral monitoring in the OR and the ICU.- 1.2 Why monitor the brain.- 1.3 The neurological approach to EEG interpretation.- 2. The principle of EEG recording using computerized power spectral analysis.- 2.1 Difference with conventional EEG recording.- 2.2 Electrode placement.- 2.3 Technical requirements to obtain a reliable EEG signal (amplifiers, filters).- 2.4 The recording procedure.- 2.5 Display techniques of the EEG.- 2.6 Artifact rejection during processed EEG measurement.- 2.7 Signal conduction and conversion.- 3. Set-up of monitoring the EEG: The electrode montage.- 4. Anesthesia and the EEG.- 4.1 Rationale for the use of the EEG in anesthesia.- 4.2 Inhalational agents and their effect on the EEG (N2O, halothane, enflurane, isoflurane).- 4.3 Intravenous agents and their effect on the EEG (barbiturates, etomidate, ketamine, opioids, benzodiazepines, propofol, CO2).- 5. The EEG and cerebral ischemia.- 5.1 Differentiation between ischemia and anesthetic-induced EEG changes.- 5.2 Cerebral monitoring during hypothermia and extracorporeal circulation (ECC).- 5.3 EEG monitoring during carotid endarterectomy.- 6. Cerebral monitoring in the intensive care unit.- 6.1 Introduction: Representative case reports.- 6.1.1 Epileptogenic activity.- 6.1.2 Monitoring in head trauma.- 6.1.3 EEG post-cerebral malperfusion.- 6.1.4 Sedation in an ICU setting.- 6.1.5 EEG power spectra post mitral valve replacement.- 6.1.6 EEG power spectra and focal seizures.- 6.1.7 EEG power spectra and benzodiazepine intoxication.- 6.1.8 EEG measurements to differentiate between drug overdose and brain lesions.- 6.1.9 The ‘diagnostic window’ in long-term sedation.- 6.2 EEG power spectra to differentiate between severe head trauma and drug overdose.- 6.3 Symptoms of irreversible cessation of functions of the brain including the brain stem.- 6.4 Avoiding false interpretation of EEG signal.- 6.4.1 Electrical interference and the EEG signal.- 6.4.2 Artifacts arising from the patient.- 6.5 EEG power spectra during sleep.- 7. Trouble shooting.- 8. Systems currently available for processed EEG recording.- 8.1 Introduction.- 8.2 Description of units used for EEG power spectral analysis in the OR and the ICU.- 9. Sensor Evoked Potentials (SEPs).- 9.1 What they are and what they offer.- 9.2 Rationale for the use of EPs in the OR and the ICU.- 9.3 The classification of EPs.- 10. The principle of Somatosensory Evoked Potential monitoring.- 10.1 Electrode types.- 10.2 Procedure for locating the exact stimulus site.- 10.3 The stimulus necessary for SEP recording.- 10.4 Recording electrodes.- 10.5 Procedure for head measurements to determine electrode location.- 10.6 Accessory for electrode placement and removal.- 10.7 Connection of electrodes with the preamplifier.- 10.8 Trouble shooting to eliminate high impedance and electrical noise.- 10.9 The differential amplifier for EEG and EP measurements.- 11. Optimising signal to-noise ratio.- 11.1 Introduction.- 11.1.1 Filtering of noise within the recording machine.- 11.1.2 The process of averaging.- 11.1.3 The stimulus rate.- 11.1.4 Stimulus repetitions (sweeps).- 11.1.5 The analysis time.- 11.2 Procedure to locate the optimal stimulus site.- 11.3 Alternating recording and stimulus sites.- 12. Evaluating the response of the evoked potential.- 12.1 Median nerve evoked potential.- 12.2 The posterior tibial nerve evoked potential.- 12.3 Criteria for abnormalities of both median and posterior tibial evoked potential.- 13. The effect of drugs on the evoked potential.- 13.1 Application of SEP monitoring in the clinical setting.- 13.2 Representative examples of SEP traces at different clinical situations.- 13.3 Postoperative use of SEPs.- 14. Use of evoked potentials in the ICU.- 14.1 Introduction.- 14.2 SEPs in the diagnosis of lesions in the plexus of the upper extremities and in cervical root lesions.- 14.3 Use of SEP monitoring in head trauma, vascular disease, and brain death.- 14.4 Pitfalls and pointers for SEP measurement in the OR and the ICU.- 15. Auditory Evoked Potentials (AEPs) and Brainstem Auditory Evoked Response (BAER or BAEP).- 15.1 Auditory Evoked Potentials.- 15.2 Clinical applications of BAER.- 16. Visual Evoked Potentials (VEPs).- Summary on the application of intraoperative EP monitoring.- 17. Complications that arise during EP monitoring.- 18. Systems of use for EP measurements in the OR and the ICU.- 19. New scopes in cerebral monitoring by topographic mapping of EEG-power spectra and EP waves.- 20. Appendix.- 20.1 Care of electrodes.- 20.2 Summary of the clinical applications of EP monitoring in the OR.- 20.3 Summary of the clinical applications of EP monitoring in the ICU.- 21. Glossary.- 22. Bibliography.- Index of subjects.