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CNS Monitoring
| The electroencephalogram (EEG) is being used to monitor the central nervous system, and evoked potentials provide a method to evaluate the intactness of neural pathways. Jugular venous saturation reflects the state of cerebral blood delivery. |
| Electroencephalogram |
| The EEG is a monitor of cerebral function that provides early evidence of cerebral ischemia, as during carotid endarterectomy or cardiopulmonary bypass. The EEG has also been advocated to monitor the depth of anesthesia. During periods of cerebral ischemia or while the patient is under general anesthesia, EEG activity generally decrease in both amplitude and frequency. The complexity of the EEG and its interpretation, plus variable and often unpredictable effects of events (changes in body temperature, alterations in PaCO2) and anesthetic drugs on the EBO tracing, detract from the frequent use of this monitor. |
| Evoked Potentials |
| Evoked potentials are the electrophysiologic responses of the nervous system to sensory stimulation (somatic, auditory, visual) that allow assessment of the functional integrity of neural pathways during anesthesia. For example, somatosensory evoked potentials are produced by application of small electrical currents that stimulate a peripheral nerve, such as the median nerve at the wrist or posterior tibial nerve at the ankle. The resulting recorded evoked potential reflects the intactness (or interruption) of neural pathways from the peripheral nerve through the spinal cord to the somatosensory cortex. This type of monitoring is particularly useful in confirming the intactness of the sensory spinal cord pathways in anesthetized patients under-going procedures on the spine. This type of monitoring does not assess the integrity of motor spinal cord pathways. Monitoring of motor evoked is not yet commercially available. 'volatile anesthetics, especially in high concentrations, and hypothermia may produce changes in the latency period and amplitude of evoked potentials that are similar to alterations produced by neural ischemia. As with the EEG, the complexity and cost of evoked potential monitoring limit its frequent use. |
| Jugular Venous Saturation |
| This represents the global delivery and extraction of oxygen to the brain. To date it is not widely used and its value is debated. Nevertheless, declines in saturation do correlate with cerebral ischemia. |
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