Intraoperative Neurophysiologic Monitoring
DESCRIPTION
Intraoperative neurophysiologic monitoring describes a variety of procedures that have been used to monitor the integrity of neural pathways during high-risk neurosurgical, orthopedic, vascular and other surgeries that may damage the nervous system. The principal goal of intraoperative monitoring is the identification of nervous system impairment in the hope that prompt intervention will prevent permanent deficits. There are two types of intraoperative neurophysiological monitoring. The first type uses techniques to identify impending damage to the nervous system. The surgeon is alerted to the possible damage, and corrective action is taken to prevent the damage. The second uses mapping techniques to identify critical structures in the nervous system. Once identified electrophysiologically, the surgeon avoids these structures to prevent neurological damage from occurring. Correctable factors that can occur during surgery include circulatory disturbance, excess compression from retraction, bony structures or hematomas, or mechanical stretching. There are various types of intraoperative monitoring described below.
Sensory-evoked Potentials
Sensory-evoked potential describes the responses of the sensory pathways to sensory or electrical stimuli. Intra-operative monitoring of sensory-evoked potentials is used to assess the functional integrity of central nervous system (CNS) pathways during operations that put the spinal cord or brain at risk for significant ischemia or traumatic injury. The basic principles of sensory-evoked potential monitoring involves identification of a neurological region at risk, selection and stimulation of a nerve that carries a signal through the at-risk region, and recording and interpretation of the signal at certain standardized points along the pathway. While monitoring the neural pathway at risk, another sensory pathway is monitored as a control. The control recording provides a method of differentiating the normal changes in the nerve pathway from the changes that occur as a result of the high-risk surgery that would place the neural pathway at risk. Sensory-evoked potentials can be further broken down into the following categories according to the type of simulation used:
Somatosensory-evoked potentials (SSEPs) are electrical waves that are generated by the response of sensory neurons to stimulation. Peripheral nerves, such as the median ulnar or tibial nerve, are typically stimulated, but in some situations the spinal cord may be stimulated directly. Recording is done over peripheral nerve, spinal cord, and brainstem and at the cortical level. SSEPs are used as a mapping technique to record directly from the cerebral cortex to identify the sensory areas of the cortex. Intra-operative monitoring of SSEPs is most commonly used during orthopedic or neurologic surgery in order to provide prompt intervention and reduce surgically induced morbidity and/or to monitor the level of anesthesia. Several different techniques are commonly used, including stimulation of a relevant peripheral nerve with monitoring from the scalp, from interspinous ligament needle electrodes, or from catheter electrodes in the epidural space.
Brainstem auditory evoked potentials (BAEPs) are generated in response to auditory clicks and can define the functional status of the cochlea, the auditory nerve, the brainstem and the primary auditory cortex.
Visual-evoked potentials (VEPs) are used to track visual signals from the retina to the occipital cortex using light flashes as a stimulating signal. VEPs are helpful as a mapping technique to identify visual system structures during tumor removal.
EMG (Electromyogram) Monitoring and Nerve Conduction Velocity Measurements
This type of monitoring can be performed in the operating room and may be used to assess the status of the peripheral nerves, (e.g., to identify the extent of nerve damage prior to nerve grafting or during resection of tumors). Additionally, these techniques may be used during procedures around the nerve roots and around peripheral nerves to assess the presence of excessive traction or other impairment. Surgery in the region of cranial nerves can be monitored by electrically stimulating the proximal (brain) end of the nerve and recording via EMG in the facial or neck muscles. Thus the monitoring is done in the direction opposite to that of sensory-evoked potentials, but the purpose is similar - to verify that the neural pathway is intact.
Motor -evoked Potential Monitoring
This involves stimulating the motor cortex and recording muscle responses from the arms, legs and face. There are three techniques of stimulating the motor cortex. The first is transcutaneous electrical stimulation with needle electrodes inserted in the scalp over the motor cortical strip. The second is transcutaneous magnetic stimulation with a magnetic coil placed on the scalp over the motor cortex. These monitoring techniques can prevent damage from occurring to the brainstem, spinal cord, nerve root and peripheral nerves. The third type is primarily a mapping technique that is used to identify the motor parts of the cerebral cortex, and involves direct stimulation of the motor cortex with electrodes directly on the cortex. It can also be used as a monitoring technique to prevent damage from occurring during tumor removal.
EEG (Electroencephalogram) Monitoring
Spontaneous EEG monitoring can also be recorded during surgery and can be subdivided as follows:
EEG monitoring has been widely used to monitor cerebral ischemia secondary to carotid cross clamping during a carotid endarterectomy. EEG monitoring may identify those individuals who would benefit from the use of a vascular shunt during the procedure in order to restore adequate cerebral perfusion. Conversely, shunts, which have an associated risk of iatrogenic complications, may be avoided in those individuals in whom the EEG is normal. Carotid endarterectomy may be done under local anesthesia so that monitoring of cortical function can be directly assessed.
Electrocorticography (ECoG) is the recording of the EEG directly from a surgically exposed cerebral cortex. ECoG is typically used to define the sensory cortex and to map the critical limits of a surgical resection. ECoG recordings have been most frequently used to identify epileptogenic regions for resection. In these applications, electrocorticography does not constitute intraoperative monitoring.
POLICY
Intraoperative neurophysiologic monitoring, including, but not limited to the following: Somatosensory-evoked potentials, brainstem auditory-evoked potentials, visual-evoked potential, EMG, motor-evoked potentials, and EEG, when performed during spinal, intracranial, or vascular procedures, is considered medically necessary if the medical appropriateness criteria are met. (See Medical Appropriateness below.)
Intraoperative neurophysiologic monitoring for other indications is considered investigational.
Any device utilized for this procedure must have FDA approval specific to the indication, otherwise it will be considered investigational.
See also: Visual and Auditory Evoked Potentials
MEDICAL APPROPRIATENESS
Somatosensory-evoked potentials (SSEPs), when used for any surgical procedure involving the spinal levels C1 - L2 OR Electromyograms (EMGs), when used for any surgical procedure involving the spinal levels C1 - S1, are considered medically appropriate if the following criteria are met:
Documentation of involvement of monitoring instrumentation that can effectively monitor tissue at risk, and documentation of exposure of multiple nerve roots at one or more levels of the spinal cord; or
Documentation of the existence of a need to monitor the connections between nerve roots and monitoring multiple muscles at multiple levels to detect possible injury to those connection
Somatosensory-evoked potentials (SSEPs); OR EEG (Electroencephalogram) Monitoring for cerebral vascular surgical procedures used to restore normal anatomy and blood flow to cerebral artery complex including carotids, vertebral arteries, and cerebral arteries (e.g., carotid endarterectomies, cerebral aneurysms) are considered medically appropriate.
Brainstem auditory - evoked potentials (BAEPs) for any surgical procedure on or near the acoustic nerve, inner ear or brainstem is considered medically appropriate.
Visual-evoked potentials (VEPs) for any procedure on or near the optic nerve, cortex or chiasm are considered medically appropriate.
ADDITIONAL INFORMATION
Evoked potential studies are to be performed by the physician alone or by a technologist under direct supervision of the electrodiagnostic (EDX) consultant. The consultant must be trained or certified in the application, performance and interpretation of electrodiagnostic testing and licensed by the state in which the studies are performed. The technician performing the studies must be trained in electrodiagnostic testing and licensed or certified by the state (or by one of the state's health related boards if licensure or certification as a technician does not exist in a given state) in which the studies are performed. Electrodiagnostic testing is not performed in a standard fashion, but must be specifically designed for each individual patient. It is often necessary to modify or add to the procedure during the examination, depending on the findings as they unfold. For this reason, collection of the clinical and electrophysiologic data must be entirely under the supervision of an EDX consultant who is physically present in the facility in which the studies are performed and actively involved in the examination of the findings as they unfold. (Refer to BCBST's Staff Supervision Requirements for Delegated Services policy.)
According to the American Association of Electrodiagnostic Medicine, becoming credentialed by a national examining organization that assesses accuracy of knowledge of evoked potentials (EP) is the only objective method of demonstrating competency in the interpretation of EP studies. Eligibility requirements for the American Board of Electrodiagnostic Medicine examination include the completion of an accredited residency in neurology or physical medicine and rehabilitation with a minimum of 6 months of full-time equivalent formal clinical neurophysiology training and Board certification by the American Board of Psychiatry and Neurology (neurology or psychiatry) or the American Board of Physical Medicine and Rehabilitation (physiatry). One year of additional post-residency experience is also required.
Resnick et al summarized that, “based on the medical evidence provided by the literature reviewed, there does not appear to be support for the hypothesis that any form of intraoperative monitoring improves patient outcomes following lumbar decompression or fusion procedures for degenerative spinal disease. Evidence does indicate that a normal evoked EMG response is predictive for intrapedicular screw placement (high NPV for breakout). The presence of an abnormal EMG response does not, however, exclude intrapedicular screw placement (low PPV). The majority of clinically apparent postoperative nerve injuries are associated with intraoperative changes in SSEP and/or DSEP monitoring. For this reason, changes in DSEP/SSEP monitoring appear to be sensitive to nerve root injury. There is a high false-positive rate, however, and changes in DSEP and SSEP recordings are frequently not related to nerve injury. A normal study has been shown to correlate with the lack of a significant postoperative nerve injury. There is no substantial evidence to indicate that the use of intraoperative monitoring of any kind proves useful information to the surgeon in terms of assessing the adequacy of nerve root decompression at the time of surgery”.
There is a lack of published studies to validate the use of intraoperative neurophysiologic monitoring for other indications.
SOURCES
American Academy of Neurology. (1990). Assessment: Intraoperative neurophysiology. Report of the therapeutics and technology assessment subcommittee of the American Academy of Neurology. Neurology, 40 (11), 1644-6.
American Association of Electrodiagnostic Medicine. (1998, February). Responsibilities of an electrodiagnostic technologist: Position Statement. (Endorsed by the American Association of Electrodiagnostic Technologists August 1998.) Retrieved June 24, 2009 from http://www.aaet.info/resources/responsibilities_of_an_edxtech.cfm.
American Association of Electrodiagnostic Medicine. (2002). American Academy of Neurology, and American Academy of Physical Medicine and Rehabilitation. Recommended Policy for Electrodiagnostic Medicine. Retrieved June 24, 2009 from http://www.aanem.org/documents/recpolicy.pdf.
American Association of Neuromuscular & Electrodiagnostic Medicine. (1999, May). Technologists conducting nerve conduction studies and somatosensory evoked potential studies independently to be reviewed by a physician at a later time: Position Statement. Retrieved June 24, 2009 from http://www.aanem.org/documents/techs_conducting_ncs_sep.PDF.
American Association of Neuromuscular & Electrodiagnostic Medicine. (1999, May). Who is qualified to practice electrodiagnostic medicine?: Position Statement. Retrieved June 24, 2009 from https://www.aanem.org/documents/who_is_qualified.PDF.
American Association of Neuromuscular & Electrodiagnostic Medicine. (2000, April). The role of electrodiagnostic technologists in the operating room: Position Statement. Retrieved June 24, 2009 from http://www.aanem.org/PracticeIssues/PositionStatements/job_descriptions_for_edxtech.cfm.
American Association of Neuromuscular & Electrodiagnostic Medicine. (2000, February). Job descriptions for electrodiagnostic technologists: Position Statement. (Endorsed by the American Society of Electroneurodiagnostic Technologists April 2000.) Retrieved June 24, 2009 from http://www.aanem.org/documents/job_descriptions_edx_techs.PDF.
American Electroencephalographic Society. (1987). American Electroencephalographic Society Guideline. Journal of Clinical Neurophysiology, 4 (4), 397-416.
American Electroencephalographic Society. (1994). Guideline eleven: Guidelines for intraoperative monitoring of sensory evoked potentials. Journal of Clinical Neurophysiology, 11 (1), 77-87.
BlueCross BlueShield Association. Medical Policy Reference Manual. (2:2004). Intra-operative neurophysiologic monitoring (sensory-evoked potentials, motor-evoked potentials, EEG monitoring) (7.01.58). Retrieved June 24, 2009 from BlueWeb.
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Hayes. Medical Technology Directory. (2006). Somatosensory Evoked Potentials (SEPs) for Intraoperative Monitoring (IOM) during Surgery for Scoliosis. Retrieved May 17, 2006 from www.Hayesinc.com/subscribers. (18 articles and/or guidelines reviewed)
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Kelleher, M.O., Tan, G., Sarjfant, R. & Fehlings, M.G. (2008) Predictive value of intraoperative neurophysiological monitoring during cervical spine surgery: a prospective analysis of 1055 consecutive patients. Journal of Neurosurgery. Spine, 8 (3), 215-221.
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McGill University Health Centre. (2005, July). Use of intraoperative neurophysiological monitoring during spinal surgery: Report number 20. Retrieved January 31, 2006 from http://www.mcgill.ca/files/tau/SPINAL_MONITORING_Final.pdf.
Resnick, D.K., Choudhri, T.F., Dailey, A.T., Groff, M.W., Khoo, L., Matz, P.G., et al. (2005). Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 15: electrophysiological monitoring and lumbar fusion. Journal of Neurosurgery: Spine. 2 (6), 725-732.
U. S. Food and Drug Administration. (2005, August). Center for Devices and Radiological Health. 510 (K) Summary. Retrieved June 24, 2009 from http://www.accessdata.fda.gov/cdrh_docs/pdf5/K050798.pdf.
ORIGINAL EFFECTIVE DATE: 1/1985
MOST RECENT REVIEW DATE: 9/10/2009
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