In general, it is the presence of neurologic deficit, either sensory or motor, in the distribution of the respective nerve root, and not the pain, that makes an indication for surgery. Decompressive spine surgery is almost always extradural. There are two main types of approaches for decompressive surgery: anterior approach and posterior approach. These approaches differ in positioning of the patient, surgical maneuvers, and type of associated risks for neurologic compromise. This chapter describes the step-by-step approach to neuromonitoring in decompressive surgery. Like in any other surgical procedure, performing reliable and informative intraoperative neurophysiologic monitoring in decompressive spine surgery requires not only solid technical and theoretical knowledge of all the tests employed, but also a good understanding of the critical points in the surgery. It requires close coordination between the neurophysiology, surgery, and anesthesia teams.
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The success of intraoperative neurophysiology relies on the ability of the neurophysiologist to use all the tests available at hand in the outpatient lab appropriately and adapt them to the specific environment of the operating room (OR) for different surgical procedures. This chapter provides an overview of the tests that constitute the “tools” in the OR. The chapter mentions special techniques of more limited use, which are derived from the main ones (e.g., bulbocavernosus reflex, dorsal column mapping techniques). It gives a practical introduction to each of the main neurophysiological methods used in the OR regarding: (a) the principle it is based on; (b) the methodology for stimulation and recording; (c) the electrical potentials to be recorded, their correlation with neuroanatomy, their main value in intraoperative monitoring and mapping, and key points in their interpretation; and (d) a summary of each method’s applications in different types of surgery.
Electroencephalogram and electrocorticography (ECoG) are two powerful tools in the field of intraoperative neurophysiology. ECoG has a net advantage over intraoperative EEG because it offers a significantly higher resolution of the recordings and the opportunity of a more versatile setup. The latter is both an advantage as well as a necessity given the variability in the size of the exposed cortex, deriving from the dimensions of the craniotomy or from the accessibility to the different structures (e.g., mesial temporal structures or challenging cortical exposure as in the case of a highly adherent dura). This chapter provides a brief description on ECoG in nonepilepsy surgery. Whether it is through early detection of stimulation-induced epileptifom discharges, appreciation of depth of anesthesia or of baseline cortical excitability, guidance of seizure management or detection of cortical ischemia, ECoG delivers unique information that increases the safety of supratentorial surgeries.
Cardiac, ascending aorta, and aortic arch surgeries are complex procedures that carry high morbidity and mortality risks. They can result in multisystem failure, with the brain being among the vital organs at increased risk of injury. This chapter addresses the specifics and challenges of neurophysiologic monitoring, from a single test to a multimodality approach, in cardiac and thoracic aorta surgery performed under hypothermic circulatory arrest with the use of cardiopulmonary bypass (CPB). Neurophysiologic monitoring is a valuable neuroprotective tool during surgeries performed via CPB under hypothermic conditions. However, the reliability of the information delivered depends on a clear understanding of the role of monitoring within the context of the surgery and preoperative planning. Its value relies on the neurophysiologist’s familiarity with the particularities of monitoring under the specific conditions present in these procedures (e.g., hypothermia), as well as on his/her expertise with the tests used, in particular with the EEG.
Spinal cord ischemia (SCI) remains a potentially devastating complication of thoracic (TA) and thoracoabdominal aneurysm (TAA) repair with a historic incidence of 16% in Crawford’s benchmark series. This chapter reviews the contemporary management of TAA (both open and endovascular repair) with emphasis on the role of intraoperative neurophysiology to detect and correct spinal cord ischemia before permanent neurological deficit occurs. It describes the additional benefits of somatosensory evoked potentials, muscle motor-evoked potentials induced by transcranial electrical stimulation, and EEG monitoring (i.e., detection of cerebral and limb ischemia). Besides intraoperative neuromonitoring, the chapter also addresses the techniques that can be employed to maintain adequate spinal cord perfusion along with known neuroprotective adjuncts that are used during these procedures. Although spinal cord injury remains a devastating complication of open repair of the thoracic aorta, the rate of paraplegia has significantly decreased with the use of current adjuncts and surgical techniques.
Surgery of the peripheral nervous system is performed commonly. Its usual indications include treatment of nerve root compression, peripheral nerve entrapments, traumatic nerve injuries, and nerve or root tumor resections. This chapter describes the use of intraoperative neurophysiology in surgeries involving the peripheral nerves. It begins with a detailed diagnostic approach in localizing and establishing the type of injury, determining the severity of peripheral nerve involvement, and the preoperative diagnostic tests that will help plan the appropriate surgical intervention. Afterward, the chapter presents the specifics of intraoperative neurophysiologic testing in three types of peripheral nerve surgery: surgical treatment of posttraumatic nerve injury, nerve tumor resection, and minimally invasive surgery with a high risk of peripheral nerve damage. The chapter concludes with examples of common clinical scenarios as well as a few anesthetic considerations.
It is known that aggressive removal of gliomas has a positive impact on survival rate and the quality of life in both adults and children. This is also the case of highly aggressive tumors such as glioblastoma multiforme where a high resection rate has been shown to correlate with better prognosis. This chapter is dedicated to intraoperative neurophysiologic mapping and monitoring of sensorimotor, language, parietal, and visual functions. It provides a brief description on maximal resection and maximal safe resection. It discusses preoperative mapping techniques, and intraoperative neurophysiologic mapping techniques. It then provides a detailed summary of the potential effects on functional mapping and monitoring procedures of the most common anesthetics and drugs used during supratentorial surgery. The chapter finally summarizes specifics resulting from the type of clinical application (i.e., type of surgery) of different functional mapping and monitoring procedures.
This chapter addresses the principle, methodology, interpretation, and technical and theoretical challenges associated with intraoperative neurophysiologic mapping and monitoring of language and higher parietal functions. Understanding the functional anatomy (i.e., the neurophysiological–neuroanatomical correlation) of the structures to be mapped, helps choosing the correct tasks for testing the patient, based on the lesion location. The chapter describes the functional language and parietal anatomy as described in the literature. To perform a successful mapping, practical tasks must be selected that are both essential and feasible in an operative setting. Cortical and subcortical mapping is essential to safely operate in eloquent cortical or subcortical cortex. Preoperative planning and intraoperative direct stimulation allows the surgeon to approach lesions that had traditionally been considered inoperable. One of the most important steps to be taken for ensuring a successful mapping procedure is teamwork, planning, and clear communication between the neurophysiologists, surgical, anesthesia, and nursing teams.
Understanding the mechanism of action of different anesthetics and of physiologic parameters, and thus, the consequent impact on different neurophysiologic tests is essential for reliable interpretation of changes seen during neuromonitoring. This chapter explains how the most commonly used anesthetics will impact different neurophysiologic tests used in intraoperative monitoring, and how we can control for such influences to give reliable and clinically meaningful feedback during surgeries. It starts with a brief discussion on how anesthetic agents affect potentials in a general sense. The chapter then discusses the most commonly used agents, their mechanisms of action, and their specific effects on different types of evoked potentials. It explains the importance of assessing the depth of anesthesia and how we can do it as well as on the concept of anesthetic fade effect. The chapter concludes with a discussion of the effects of several physiologic parameters on the neurophysiologic recordings.