BlueCross and BlueShield of Montana Medical Policy/Codes
Intraoperative Neurophysiological Monitoring
Chapter: Surgery: Administrative
Current Effective Date: September 24, 2013
Original Effective Date: March 18, 2012
Publish Date: June 24, 2013
Revised Dates: This medical document is no longer scheduled for routine literature review and update. June 24, 2013

Intraoperative neurophysiologic monitoring describes a variety of procedures that have been used to monitor the integrity of neural pathways during high-risk neurosurgical, orthopedic and vascular surgeries.  The principal goal of intraoperative monitoring is the identification of nervous system impairment in the hope that prompt intervention will prevent permanent deficits. Correctable factors at surgery include circulatory disturbance, excess compression from retraction, bony structures or hematomas, or mechanical stretching.  The various different methodologies of monitoring are described below.

Sensory Evoked Potentials Sensory evoked potentials describe the response of the sensory pathways to sensory or electrical stimuli.  Intraoperative 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 risk region, and recording and interpretation of the signal at certain standardized points along the pathway.  Monitoring of sensory evoked potentials is commonly used during the following procedures: carotid endarterectomy, brain surgery involving vasculature, surgery with distraction compression or ischemia of the spinal cord and brainstem, and acoustic neuroma surgery.  Sensory evoked potentials can be further broken down into the following categories according to the type of stimulation used:

  • Somatosensory Evoked Potentials (SSEPs) are electrical waves that are generated by the response of sensory neurons to stimulation.  Intraoperative monitoring of SSEPs is most commonly used during orthopedic or neurologic surgery in order to prompt intervention to reduce surgically induced morbidity and/or to monitor the level of anesthesia.  One of the most common indications for SSEP is in patients undergoing corrective surgery for scoliosis. In this setting, SSEP monitors the status of the posterior column pathways, and thus does not reflect ischemia in the anterior (motor) pathways.  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 auditory nerve.  Surgical resection of a cerebellopontine angle tumor, such as an acoustic neuroma, places the auditory nerves at risk and BAEPs have been extensively used to monitor auditory function during these procedures.
  • Motor Evoked Potentials (MEPs) are generated by either electrical or magnetic stimulation of the motor cortex or the spinal cord.  Recordings are obtained either as neurogenic potential in the distal spinal cord or peripheral nerve, or as myogenic potential from the innervated muscle.  Transcranial electrical stimulation involves stimulation of electrodes on the scalp, or if the brain is exposed by a craniotomy, stimulation of electrodes placed directly on the brain surface.  Electrical stimulation also can be applied directly over the spinal cord when a laminectomy affords exposure proximal to the lesion in question.  Transcortical magnetic stimulation delivers a pulsed magnetic field over the scalp in the region of the primary motor cortex.  However, generating good signals in the operating room with this technique is difficult and the devices to produce a magnetic field can be a hindrance in surgery.
  • Visual Evoked Potentials (VEP's) are used to track visual signals from the retina to the occipital cortex using light flashes.  VEP monitoring has been used for surgery on lesions near the optic chiasm.  However, VEP's are very difficult to interpret due to their sensitivity to anesthesia, temperature and blood pressure.

Electromyogram Monitoring (EMG) 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).

Electroencephalogram (EEG) and Electrocorticography (ECoG) 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 patients 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 patients 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 monitoring per SE.

Prior authorization is recommended. Call Blue Cross and Blue Shield of Montana (BCBSMT) Customer Service at 1-800-447-7828 or fax your request to the Medical Review Department at 406-441-4624. A retrospective review is performed if services are not prior authorized.

Medical Necessity

BCBSMT may consider the following types of intraoperative monitoring medically necessary during spinal, intracranial, or vascular procedures when such procedures have a risk of significant complications(s) that can be detected and prevented through use of neurophysiological monitoring:

  • Somatosensory evoked potentials (SSEPs),
  • Brainstem auditory evoked potentials (BAEPs),
  • Electromyography (EMG) of cranial or spinal nerves,
  • Electroencephalography (EEG),
  • Electrocorticography (ECoG), and
  • Motor evoked potentials (MEPs) performed with SSEPs.

Note:  To be a separate reimbursable service, Intraoperative Monitoring must:

    1. Be provided to the operating surgeon (ordering physician) by a licensed physician separate from the surgical team (operating surgeon, assistant surgeons, and/or anesthesiologists); AND
    2. Have the interpreting physician physically in attendance in the operating suite; OR
    3. Provide documentation from the operative report that the interpreting physician be present by means of real-time remote mechanism for all electro neurodiagnostic (END) monitoring situations with the following stipulations:
      • The interpreting physician is constantly available to interpret the recording and advise the surgeon; AND
      • There is a live video representation of the END monitoring (identical to the information seen by the technician) with a high-quality bi-directional live audio connection that allows the remote interpreting physician to converse with the operating surgeon at any time.
        • A cell phone connection or cellular walkie-talkie is not considered adequate.
        • "Live" means contemporaneous monitoring by the physician during the surgery.  Review of a CD or other documentation post-operatively does not constitute "live monitoring".

Not Medically Necessary

BCBSMT considers intraoperative EMG and nerve conduction velocity monitoring on the peripheral nerves during surgery not medically necessary.

Advanced Member Notice of Financial Liability for Denied Services

When the criteria for coverage is not met, BCBSMT encourages all participating providers to have a member complete and sign an Advanced Member Notification (AMN) form stating that BCBSMT will not cover this service, supply, device, or drug. If an AMN is signed prior to delivery of the service, participating providers can balance bill the patient. If an AMN is not signed, participating providers are financially liable and cannot balance bill the BCBSMT member for denied services. Services provided by an out-of-state provider that are denied as not medically necessary are the financial responsibility of the patient.

Refer to the Advanced Member Notification medical policy for more information. The AMN form is available at  (Click on Providers and then Forms).


BCBSMT considers intraoperative monitoring experimental, investigational and unproven for intraoperative visual evoked potentials (VEPs), and motor evoked potentials (MEPs) performed without somatosensory evoked potentials (SSEPs).

Federal Mandate

Federal mandate prohibits denial of any drug, device, or biological product fully approved by the FDA as investigational for the Federal Employee Program (FEP). In these instances coverage of these FDA-approved technologies are reviewed on the basis of medical necessity alone. Call the BCBSMT FEP Customer Service Department at 1-800-634-3569 for benefit information.

Rationale for Benefit Administration

This medical policy was developed through consideration of peer reviewed medical literature, FDA approval status, accepted standards of medical practice in Montana, Technology Evaluation Center evaluations, and the concept of medical necessity. BCBSMT reserves the right to make exceptions to policy that benefit the member when advances in technology or new medical information become available.

The purpose of medical policy is to guide coverage decisions and is not intended to influence treatment decisions. Providers are expected to make treatment decisions based on their medical judgment. Blue Cross and Blue Shield of Montana recognizes the rapidly changing nature of technological development and welcomes provider feedback on all medical policies.

When using this policy to determine whether a service, supply or device will be covered please note that member contract language will take precedence over medical policy when there is a conflict.


Intraoperative monitoring is a widely accepted practice.  Studies have shown effectiveness of intraoperative monitoring in improving surgical outcome.  SSEP is the standard of intraoperative monitoring, with excellent ability to assess dorsal column and lateral sensory tract function, and the ability to detect changes in function of anterior motor tracts by stimulating mixed sensorimotor peripheral nerves.  However, significant motor deficits have been seen in patients undergoing spinal surgery despite normal SSEPs.  MEPs were developed to better the motor neurophysiological pathways.  Note that anesthetic agents can severely diminish the motor evoked responses.  Studies and reports suggest there is evidence to support the use of intraoperative neurophysiological monitoring during spinal surgery, and that using SSEPs and MEPs substantially diminishes that risk.   Intraoperative spinal cord injury during spinal surgery generally compromises both motor and somatosensory pathways.  Therefore, the use of both of these independent techniques in parallel has been proposed and is seen as a safeguard should one of the monitoring techniques fail.  Combined SSEP and MEP monitoring has been shown to have greater sensitivity than SSEP alone.   At this time the scientific evidence is differing on the intraoperative use of VEPs and its use has not become standard practice.


Disclaimer for coding information on Medical Policies

Procedure and diagnosis codes on Medical Policy documents are included only as a general reference tool for each policy.  They may not be all-inclusive.

The presence or absence of procedure, service, supply, device or diagnosis codes in a Medical Policy document has no relevance for determination of benefit coverage for members or reimbursement for providers.  Only the written coverage position in a medical policy should be used for such determinations.

Benefit coverage determinations based on written Medical Policy coverage positions must include review of the member’s benefit contract or Summary Plan Description (SPD) for defined coverage vs. non-coverage, benefit exclusions, and benefit limitations such as dollar or duration caps. 

Rationale for Benefit Administration
ICD-9 Codes
00.94. Refer to the ICD-9-CM manual
ICD-10 Codes
C71.0 – C71.9, C79.31 – C79.32, D33.0 – D33.9, D43.0 – D43.9, D49.6, I71.00 – I71.9, M50.00 – M50.93, M48.00 – M48.08, M40.00 – M40.57, M41.00 – M41.9, I65.01 – I65.9, 4A0002Z, 4A0004Z, 4A000BZ, 4A00X2Z, 4A00X4Z, 4A01029, 4A0102B, 4A01329, 4A0132B, 4A01X29, 4A01X2B, 4A1002Z, 4A1004Z, 4A100BZ, 4A10X2Z, 4A10X4Z, 4A11029, 4A1102B, 4A11329, 4A1132B, 4A11X29, 4A11X2B, 4B00XVZ, 4B01XVZ, 4B0FXVZ, F01Z77Z F01Z87Z, F01Z8JZ, F01Z9JZ 
Procedural Codes: 92585, 92586, 95829, 95867, 95868, 95920, 95925, 95926, 95927, 95928, 95929, 95938, 95939, 95940, 95941, 95955, 95961, 95962, G0453
  1. Aminoff, M.J.  Intraoperative monitoring by evoked potentials for spinal cord surgery: the cons. Electroencephalography Clinical Neurophysiology (1989) 73(5):378–80.
  2. Daubed, J.R.  Intraoperative monitoring by evoked potentials for spinal cord surgery: the pros. Electroencephalography.  Clinical Neurophysiology (1989) 73(5):374–7.
  3. Schweiger, H. Kamp, H.D. et al.  Somatosensory-evoked potentials during carotid artery surgery: experience in 400 operations.  Surgery (1991) 109(5):602–9.
  4. American Academy of Neurology Therapeutics and technology assessment subcommittee:  Intra-operative neurophysiology Neurology (1990); 40(11):1644-6
  5. Fisher, R.S., Raudzens, P., et al.  Efficacy of intra-operative neurophysiologic monitoring.  Journal of Clinical Neurophysiology (1995) 12:97-109.
  6. Nuwer, M.R., Dawson, E.G., et al.  Somatosensory evoked potential spinal cord monitoring reduces neurologic deficits after scoliosis surgery: results of a large multicenter survey.  Electroencephalography and Clinical Neurophysiology (1995 January) 96(1):6-11.
  7. Wilson-Holden T.J., Padberg, A.M., et al, Efficacy of intraoperative monitoring for pediatric patients with spinal cord pathology undergoing spinal deformity surgery Spine (1999 August 15) 24(16):1685-92.
  8. Intraoperative Neurophysiologic Monitoring (sensory-evoked potentials, motor-evoked potentials, EEG monitoring). Chicago, Illinois: Blue Cross Blue Shield Association Medical Policy Reference Manual (2004 April) Surgery 7.01.58.
  9. Costa, P., Bruno, A., et al.  Somatosensory-and motor-evoked potential monitoring during spine and spinal cord surgery.  Spinal Cord (2007) 45:86-91.
January 2012 New Policy.
June 2013 Policy formatting and language revised.  Title changed from "Intraoperative Neurophysiologic Monitoring (sensory-evoked potentials, motor-evoked potentials, EEG monitoring)" to "Intraoperative Neurophysiological Monitoring".  Added criteria that intraoperative monitoring must be used during procedures that have a high risk of significant complications.  Added criteria for intraoperative monitoring to be a separate reimbursable service.  Added CPT codes 92586, 95928, 95929, 95940, 95941, 95961, 95962, G0453 and removed 95900, 95903, 95904, and 95930.
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Intraoperative Neurophysiological Monitoring