Monitoring the Brain and Spinal Cord

Advances in monitoring technology, as presented elsewhere in this volume, have also occurred in monitoring to the brain and spinal cord. These techniques have created the opportunity to explore function and prognosis in patients who otherwise are unable to participate in a neurologic examination. This chapter overviews the anatomy, technology, and applications of several of these techniques. Before starting, it is important to mention that, in general, these techniques are not a replacement for the neurologic examination. The complexity and breadth of examination possible with awake testing cannot be matched by these techniques. Furthermore, the clinical examination can be more sensitive than these tests. For example, clinical function becomes abnormal at reduced cerebral blood flow (approximately 25 mL/min per 100 g) above that which causes alteration in electrophysiological monitors. Each of these monitors has a variety of uses depending on the specific method of monitoring and the specific neural tracts or tissue assessed. Although these methods can detect abnormalities, there are often indistinct thresholds for when changes correlate to clinical changes or prognostication of injury. Nevertheless, these techniques have found substantial application in the care of neurosurgical patients in whom the information gathered can enhance treatment decisions and evaluate the effectiveness of management approaches.