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1. Monitors of the nervous system can monitor function or adequacy of blood flow, or both.
2. Most anesthetic drugs have a typical triphasic effect on the EEG: small doses produce activation, moderate doses produce slowing with maintenance or increase in amplitude, and large doses produce burst suppression.
3. The EEG is well established for monitoring the nervous system during carotid vascular surgery, during epilepsy surgery, and for depth of the hypnotic state. Other uses remain controversial and largely experimental.
4. Monitoring 16 or 32 channels of an analog EEG requires extensive resources, particularly with respect to personnel. Processed electroencephalographic monitors, by simplifying the display and using usually two or four channels of information, require fewer resources to use and may detect inadequate CBF during surgery nearly as well.
5. Electroencephalographic changes associated with inadequate CBF are similar to those observed with increasing doses of most anesthetic drugs.
6. Anesthetic effects on cortical SERs are significant and render monitoring of VEPs extremely difficult. Subcortical responses (i.e., auditory and somatosensory) are resistant to the effects of anesthetics. In general, the effects of intravenous drugs are less significant than those of inhaled anesthetics.
7. Electromyographic monitoring during neurologic or spinal surgery may allow the surgeon to identify nervous tissue and to detect impending damage to cranial and peripheral nerves. Use of muscle relaxant drugs is best avoided when such monitoring is used.
8. Monitoring of the motor pathways is feasible and will probably increase in coming years. Anesthetic effects may be quite significant, depending on the type of stimulation used, and precise control of the degree of muscle relaxation is necessary. Whether motor pathway monitoring with its accompanying anesthetic requirements will significantly improve our ability to monitor spinal cord or brain function remains to be seen.
9. TCD may provide information about the adequacy of CBF. More importantly, TCD readily detects emboli, and this information may help the surgeon improve technique and detect significant risk of stroke at any time during the perioperative period.
10. Measurement of SjvO₂ may help determine the balance between cerebral oxygen supply and demand. This technology has helped us better understand the effects of hyperventilation on the neurosurgical patient and contributed to the ongoing reduction in the use of hyperventilation in the neurosurgical patient. Whether this technology will gain more widespread use, particularly intraoperatively, remains unclear.
11. Cerebral oximetry is a new technology designed to measure the adequacy of CBF. Use of this device remains controversial, particularly because there is no universal agreement about normal perioperative changes and the permissible degree of intraoperative change. Much more research is required before the roles of cerebral oximetry as a neurologic monitor can be determined.