Clinical UM Guideline

Intraoperative neurophysiological monitoring uses recordings of the nervous system's electrical response to the stimulation of specific neural pathways (examples include visual, motor, auditory, general sensory evoked response studies) to obtain information on the functional integrity of pathways within the nervous system during an operative procedure. This information can assist in diagnosis of a pathological process, monitor response to therapies, identify anatomical distribution of a disease process or identify neurologic compromise. This document addresses the various types of evoked response studies and their use in intraoperative neurophysiological monitoring when the monitoring is not provided by a member of the operating team. The use of neural evoked response studies for purposes other than assistance during a surgical procedure is not addressed in this document.

Note: Please see the following related documents for additional information:

• CG-MED-24 Electromyography and Nerve Conduction Studies
• CG-MED-50 Visual, Somatosensory and Motor Evoked Potentials

Note: for a high-level overview of this document, please see “Summary for Member and Families” below.

Medically Necessary:

Intraoperative neurophysiological monitoring is considered medically necessary when ALL of the following are met:

1. The specific testing is used to monitor neural integrity during a spinal, neurologic, cranial, or vascular procedure that may compromise neurologic function; and
2. The specific testing is tailored to the clinical circumstances of the surgery. The following tests may be medically necessary when the neural pathway measured by the test is likely to be affected by the surgical procedure:
   1. Somatosensory-evoked potentials (SSEP);
   2. Brainstem auditory-evoked potentials (BAEPs);
   3. Electromyogram (EMG);
   4. Electroencephalogram (EEG);
   5. Electrocorticography (ECoG);
   6. Direct cortical stimulation;
   7. Nerve conduction velocity testing;
   8. Motor evoked potentials (MEP);
      and
3. The monitoring is ordered by the operating surgeon; and
4. The monitoring is set up and performed in the operating room by an independent technologist present at the operating site whose sole function is monitoring and transmission of data for a single case. The technologist is in continuous attendance in the operating room; and
5. A qualified individual (that is, a neurologist or a MD or PhD-level neurophysiologist) who is NOT a member of the surgical team, whose sole function is interpreting monitored data, performs real time monitored data interpretation; and
6. The surgical team (surgeon, anesthesiologist) and the monitoring team (technician, physician) have a direct, real-time communication regarding the individual’s status based on data interpretation; and
7. The monitoring physician may work from a remote site only when an independent technologist is in continuous attendance in the operating room and has the capability for real-time communication with the supervising monitoring physician; and
8. The number of individuals monitored by the physician at one time should not exceed the requirements to provide adequate attention to each individual (generally 3 or fewer simultaneous cases).

Not Medically Necessary:

The following services are considered not medically necessary in the following situations:

1. The criteria above are not met; or
2. Intraoperative neurophysiological monitoring of visual-evoked potentials; or
3. Intraoperative neurophysiological vestibular evoked myogenic potential testing; or
4. With the exception of EMG during pedicle screw stimulation, intraoperative neurophysiological monitoring used during routine spinal surgeries in the absence of myelopathy or other complicating conditions that would create significant potential risk of damage to the nerve root, plexus (for example, anterior spine access through the psoas muscle) or spinal cord.

This document describes clinical studies and expert recommendations and explains when special monitoring used during certain surgeries to protect the nerves and spinal cord is appropriate. The following summary does not replace the medical necessity criteria or other information in this document. The summary may not contain all of the relevant criteria or information. This summary is not medical advice. Please check with your healthcare provider for any advice about your health.

Key Information

Intraoperative neurophysiological monitoring (IONM) tracks how the nervous system responds to signals during surgery. It helps doctors check for possible injury to the brain, spinal cord, or nerves while an operation is happening. This monitoring uses tests like motor and sensory evoked potentials, which measure nerve responses to electric or sound signals. The goal is to catch any changes that might signal harm, so the surgical team can respond quickly. Each type of test has its strengths and weaknesses depending on the kind of surgery and the nerves involved. These tests are usually used during complex brain, spine, or blood vessel surgeries. They are only helpful if the right tests are chosen, trained experts are involved, and the surgical and monitoring teams can talk to each other in real time. Studies support using IONM in high-risk surgeries where nerves could be damaged.

What the Studies Show

Evoked response tests include somatosensory (touch), motor (movement), auditory (hearing), and muscle-based (Electromyography or EMG) monitoring. They can show if nerve function changes during surgery, possibly helping prevent long-term damage. Studies show that motor evoked potentials are better at detecting risks to movement-related nerve pathways than sensory tests. Somatosensory tests are common in spine surgeries and show high accuracy when used in high-risk groups. Brainstem auditory evoked potentials help monitor hearing-related brain areas during surgery. EMG tests can check for problems in muscles and nerves during some spine and brain procedures and are especially useful during screw placement in the spine. Monitoring is most helpful when alarms reflect true changes, especially in people at high risk. One study showed that in low-risk people, many alarms didn’t lead to problems, but in high-risk people, alarms were more likely to signal real danger. Guidelines strongly recommend monitoring for surgeries that involve the spinal cord, nerve roots, or brain. In certain spine surgeries, combining motor and sensory monitoring gives better results than either alone. Some types of monitoring, like visual and vestibular (balance) evoked potentials, are not proven to help during surgery. Professional groups note that these tests can be difficult to use in the operating room and may not be reliable. Studies also show that how often IONM is used varies widely depending on hospital, region, and individual characteristics. People with lower income or certain insurance types are less likely to receive monitoring, even when clinically appropriate.

When is Intraoperative Neurophysiological Monitoring Clinically Appropriate?

Intraoperative neurophysiological monitoring may be appropriate in these situations:

• The test is used during brain, spine, or major blood vessel surgery that may affect nerve or brain function; and
• The type of test fits the surgery being done and targets the nerves likely to be affected, such as:
  • Somatosensory-evoked potentials (SSEP)
  • Brainstem auditory-evoked potentials (BAEPs)
  • Electromyogram (EMG)
  • Electroencephalogram (EEG)
  • Electrocorticography (ECoG)
  • Direct cortical stimulation
  • Nerve conduction velocity testing
  • Motor evoked potentials (MEP)
    and
• The surgeon orders the monitoring; and
• A trained technologist is in the operating room the entire time and only works on this case; and
• A qualified expert (such as a neurologist or neurophysiologist) who is not part of the surgery team reviews the data in real time; and
• The surgical and monitoring teams communicate directly during the operation; and
• If the expert is working remotely, the technologist must be able to contact them immediately; and
• The expert monitors no more than 3 people at once to ensure each person receives enough attention.

When is this not Clinically Appropriate?

The following have not been proven to improve health and are not considered clinically appropriate:

• When the criteria above are not met
• Visual-evoked potential monitoring during surgery, because these signals are easily disrupted and difficult to read during operations
• Vestibular evoked myogenic potential testing, which lacks strong evidence for intraoperative use
• Routine spine surgeries where there is no spinal cord disease or other risk to the nerves or spinal cord (except for EMG used to check screw placement)

(Return to Description)

The following codes for treatments and procedures applicable to this guideline are included below for informational purposes. Inclusion or exclusion of a procedure, diagnosis or device code(s) does not constitute or imply member coverage or provider reimbursement policy. Please refer to the member's contract benefits in effect at the time of service to determine coverage or non-coverage of these services as it applies to an individual member.

When services may be Medically Necessary when criteria are met:

When services are Not Medically Necessary:
For the procedure codes listed above when criteria are not met or for situations designated in the Clinical Indications section as not medically necessary.

Summary

Intraoperative neurophysiological monitoring (IONP) encompasses a range of electrophysiological techniques used during surgical procedures to assess the functional integrity of neural pathways and detect impending neurological injury in real time. The evidence base, synthesized across multiple meta-analyses and a 2024 international clinical practice guideline, indicates that monitoring techniques vary in diagnostic accuracy depending on the neural pathway assessed and the surgical context. Motor evoked potentials generally demonstrate higher sensitivity than somatosensory evoked potentials for detecting motor pathway compromise. Professional society guidance supports the use of monitoring in procedures where neural structures are at risk. The strongest recommendations are for individuals at elevated risk for intraoperative spinal cord injury based on clinical and pathological characteristics. Contemporary utilization data indicate substantial growth in monitoring use over the past decade, though significant variation exists across institutions, geographic regions, and populations, suggesting that non-clinical factors influence practice patterns.

Discussion

Purpose and Principles of Intraoperative Neurophysiological Monitoring

Intraoperative neurophysiological monitoring uses recordings of the nervous system’s electrical response to stimulation of specific neural pathways to obtain information on the functional integrity of those pathways during operative procedures. Evoked response studies monitor the nerves located at or passing through operative sites, with the goal of detecting significant ischemia or injury that might put tested nerves or the spinal cord at risk. Real-time monitoring can be performed with data transmitted to an off-site monitoring center where a physician, typically a neurophysiologist, provides interpretation and alerts the surgical team if the individual’s neurological status is compromised.

The benefits of intraoperative monitoring depend on meeting several operational conditions. The American Academy of Neurology, in its Principles of Coding for Intraoperative Neurophysiologic Monitoring and Testing document (last updated July 2018), stated that effective monitoring requires a well-trained, experienced technologist present at the operating site recording and monitoring a single surgical case, supervision by a monitoring clinical neurophysiologist, preoperative anesthesia planning with continuous communication between the anesthesiologist and monitoring staff, and either physical or electronic capacity for real-time communication between the attending technologist and the supervising physician. Monitoring may be performed from a remote site only when a specifically trained technologist is in continuous attendance in the operating room with the ability for prompt real-time communication with the supervising monitoring physician. The AAN further noted that the number of cases monitored at any one time should not exceed the requirements for providing adequate attention to each; a 2010 survey of practitioners showed that on average 90% of monitoring hours are spent monitoring three or fewer simultaneous cases and that practitioners rarely monitor more than six cases simultaneously (AAN, 2018).

Professional Society Guidance and Recommendations

Several professional societies have issued guidance on the clinical applications of intraoperative neurophysiological monitoring. In January 2018, the American Association of Neurological Surgeons (AANS) and the Congress of Neurological Surgeons (CNS) Joint Section on Disorders of the Spine and Peripheral Nerves provided a Level I evidence grade for monitoring with somatosensory evoked potentials and motor evoked  potentials as a reliable tool for assessment of spinal cord integrity during surgery, with motor evoked potentials shown to be superior to somatosensory evoked potentials for this purpose. The position statement acknowledged insufficient evidence (Level III) of a therapeutic benefit from monitoring during spinal surgery, though it noted that monitoring is generally regarded as integral to lateral spine surgery. The statement recommended that monitoring be performed in procedures when the operating surgeon feels that the diagnostic information is of value, such as deformity correction, spinal instability, spinal cord compression, intradural spinal cord lesions, and procedures in proximity to peripheral nerves or roots. Spontaneous and evoked electromyography was recommended for minimally invasive lateral retroperitoneal transpsoas approaches to the lumbar spine and noted to be of potential utility during pedicle screw insertion (AANS/CNS, 2018).

In 2024, Fehlings and colleagues published a clinical practice guideline from AO Spine and PRAXIS on prevention, diagnosis, and management of intraoperative spinal cord injury. The guideline, developed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) process with systematic reviews of 164 studies encompassing 99,937 participants, recommended that intraoperative neurophysiologic monitoring be employed for high-risk individuals undergoing spine surgery. Despite the low quality of evidence as assessed by formal grading methodology, the strength of recommendation was strong based on favorable judgments regarding desirable effects, acceptability, and feasibility. The guideline listed examples of high-risk procedures such as surgery for complex spine deformity including rigid thoracic curves with high deformity angular ratio, revision congenital spine deformity, spine conditions associated with significant cord compression and myelopathy, intramedullary spinal cord tumors, unstable spine fractures including bilateral facet dislocation with disc herniation or extension-distraction injury with ankylosing spondylitis, and ossification of the posterior longitudinal ligament associated with severe cord compression and moderate to severe myelopathy. The guideline’s meta-analysis yielded pooled diagnostic accuracy estimates: for somatosensory evoked potentials, sensitivity of 67.5% (95% confidence interval [CI], 50.9% to 80.6%) and specificity of 96.8% (95% CI, 94.8% to 98.1%); for motor evoked potentials, sensitivity of 90% (95% CI, 86.1% to 92.9%) and specificity of 95.6% (95% CI, 94% to 96.7%); for electromyography, sensitivity of 48.3% (95% CI, 31.4% to 65.6%) and specificity of 92.9% (95% CI, 84.4% to 96.9%); and for multimodal monitoring, sensitivity of 91% (95% CI, 86% to 94.3%) and specificity of 93.8% (95% CI, 90.6% to 95.9%).

Somatosensory Evoked Potentials

Somatosensory evoked potentials are electrical waves generated by the response of sensory neurons to stimulation. Peripheral nerves, typically the median, ulnar, or tibial nerve, are stimulated, though in some situations the spinal cord may be stimulated directly. By stimulating the skin in various dermatomal areas, a dermatomal somatosensory evoked potential may also be recorded. The American Society of Neurophysiological Monitoring  (ASNM) published a 2024 position statement indicating that somatosensory evoked potentials are an established intraoperative monitoring modality for either localizing the human sensorimotor cortex and dorsal columns or assessing the function of the somatosensory pathways during surgical procedures in the spinal cord and brain, based on Class II and III evidence with a Type A recommendation (Toleikis, 2024).

Evidence from a 2012 guideline update by Nuwer and colleagues for the AAN and the American Clinical Neurophysiology Society (ACNS), based on multiple Class I and Class II studies, found that paraparesis, paraplegia, and quadriplegia events occurred in monitored surgeries when there were evoked potential changes and that none of these events occurred in monitored surgeries without such changes, supporting the conclusion that monitoring is effective for predicting an increased risk of adverse outcomes in individuals undergoing spinal surgery.

The diagnostic accuracy of somatosensory evoked potentials has been evaluated across several surgical contexts through meta-analyses.

For carotid endarterectomy, a meta-analysis of 15 cohort studies found that changes in somatosensory evoked potentials had a pooled specificity of 91% and sensitivity of 58%, with individuals who later had perioperative neurological deficits being 14 times more likely to have had intraoperative signal changes (Nwachuku, 2015). For cerebral aneurysm clipping surgery, pooled analysis of 13 studies yielded sensitivity of 56.8% (95% CI, 44.1% to 68.6%), specificity of 84.5% (95% CI, 76.3% to 90.3%), and a diagnostic odds ratio (OR) of 7.7 (Thirumala, 2016).

For intramedullary spinal cord tumors, analysis of eight retrospective cohort studies found pooled sensitivity of 85% (95% CI, 75% to 91%), specificity of 72% (95% CI, 57% to 83%), and diagnostic OR of 14.3 (Azad, 2018). For cervical spinal surgery, a meta-analysis of 23 studies with 7747 individuals found combined sensitivity of 46% (95% CI, 34.5% to 57.8%), specificity of 96.7% (95% CI, 93.9% to 98.2%), and diagnostic OR of 27.32 (95% CI, 13.45 to 55.50), indicating that individuals who developed a new postoperative neurologic deficit were 27 times more likely to have had a significant intraoperative change (Reddy, 2021).

The diagnostic performance of monitoring may vary substantially based on individual risk factors. Zhang and colleagues (2025) analyzed 1622 individuals undergoing cervical spinal canal decompression surgery with multimodal monitoring and found that preoperative characteristics significantly influenced alarm predictive value. In individuals with ligamentum flavum hypertrophy and/or ossification of the posterior longitudinal ligament combined with preoperative modified Japanese Orthopaedic Association score less than 12, representing a high-risk group of 287 individuals, the alarm rate was 11.15% with sensitivity of 100%, specificity of 98.84%, and positive predictive value of 90.6%. In 1335 individuals without these risk factors, the alarm rate was 2.02% with sensitivity of 91.7% and specificity of 98.79%, but positive predictive value was only 40.74%. Alarm reversibility, rather than preoperative risk factors alone, was the dominant predictor of 6-month neurological improvement (Zhang, 2025).

Motor Evoked Potentials

Motor evoked potential monitoring evaluates motor pathways located in the anterolateral spinal tracts perfused by the anterior spinal artery. This technique uses electric or magnetic stimulation of motor neural pathways in the brain or spinal cord. Electrical stimulation is accomplished by placement of surface or needle electrodes on sites that innervate areas at risk during surgery, while magnetic stimulation utilizes a magnetic coil placed on the head over the motor cortex to induce an electrical current within the brain that stimulates motor neurons.

The American Society of Neurophysiological Monitoring published a position statement indicating that intraoperative motor evoked potentials are an established option when performed by appropriately qualified personnel for localizing the motor cortex, judging subcortical proximity to corticospinal tract fibers, or monitoring motor pathways during surgical procedures that risk motor system injury in the brain, brainstem, spinal cord, or facial nerve. This recommendation was based on Class II and Class III evidence (MacDonald, 2013).

Meta-analyses have evaluated motor evoked potential diagnostic accuracy across several surgical indications.

For thoracic or thoracoabdominal aortic aneurysm surgery, analysis of 19 studies found that monitoring performed well for detecting postoperative paraplegia, with pooled sensitivity of 89.1% and specificity of 99.3% (Tanaka, 2016).

For idiopathic scoliosis correction surgery, a meta-analysis of 12 studies found pooled sensitivity of 91% (95% CI, 34% to 100%), specificity of 96% (95% CI, 92% to 98%), and diagnostic odds ratio of 250 (95% CI, 11 to 5767), indicating substantially increased odds of observing new motor deficits in individuals with significant transcranial motor evoked potential changes (Thirumala, 2017).

For intramedullary spinal cord tumors, pooled analysis of 13 studies found sensitivity of 90% (95% CI, 84% to 94%), specificity of 82% (95% CI, 70% to 90%), and diagnostic odds ratio of 55.7 (95% CI, 26.3 to 119.1) (Azad, 2018).

For cervical spine decompression surgery, an analysis of 19 studies with 4608 participants found that transcranial motor evoked potential changes had sensitivity of 56% and specificity of 94% for predicting neurological deficit, with diagnostic odds ratio of 19.26 (95% CI, 10.56 to 36.31) (Reddy, 2024).

A recent study validated specific warning criteria for motor evoked potential monitoring. Seidel and colleagues analyzed 473 intra-axial brain tumor surgeries with 3-month follow-up data available for 432 individuals. Motor evoked potential loss was associated with higher odds of motor deficit (p<0.001), and irreversible motor evoked potential alteration was associated with approximately 10 times higher odds (p<0.001). Among individuals with motor evoked potential loss, 88% had permanent deficits. Subcortical mapping motor threshold of 1 to 3 milliamperes was associated with 4 times higher odds of deficit compared to thresholds greater than 10 milliamperes (p<0.001). Among individuals with stable motor evoked potentials, 73% had no deficit, 22% had transient deficits, and 5% had mild permanent deficits (Seidel, 2025).

Hudson and colleagues (2026) conducted a multicenter retrospective review of 42 cervical endoscopic unilateral laminotomy for bilateral decompression procedures, with complete data available for 33 individuals, to assess whether intraoperative neurophysiological monitoring correlated with postoperative neurological compromise in this minimally invasive context. Of the 33 individuals, 4 (12.1%) developed postoperative weakness. All individuals with new weakness had sustained motor evoked potential decrease at closure (p<0.001), and 80% of individuals with sustained motor evoked potential decrease developed new weakness. All affected individuals had severe (Grade 3) preoperative stenosis with cord signal change (Hudson, 2026).

Brainstem Auditory Evoked Potentials

Brainstem auditory-evoked potentials (, also known as auditory brainstem evoked responses, are generated in response to auditory clicks and can define the functional status of the auditory nerve, pons, and lower midbrain. The American Society of Neurophysiological Monitoring published a position statement indicating that auditory brainstem evoked response recordings are of value during surgical procedures involving the brainstem and in assessing the function of the eighth nerve during select surgical procedures in the cerebellopontine angle. This recommendation was based on Class III evidence (Martin, 2008).

Electromyography and Nerve Conduction Velocity

Electromyography monitoring and nerve conduction velocity measurements can be performed in the operating room to assess the status of peripheral nerves, such as identifying the extent of nerve damage prior to nerve grafting or during resection of tumors. These techniques may also be used during procedures adjacent to spinal nerve roots, including dorsal rhizotomy, and 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 end of the nerve and recording via electromyography in the facial or neck muscles, verifying that the neural pathway is intact.

Placement of pedicle screws is commonly used to provide stabilization during spinal surgery. Triggered electromyography can be used to detect misplacement of pedicle screws that might cause neural damage. A 2015 meta-analysis of 11 studies found high specificity (low false-positive rate) and low sensitivity of triggered electromyography for monitoring pedicle screw placement. For surgeries in the lumbar spine, triggered electromyography predicted misplaced pedicle screw placement with pooled sensitivity of 0.55 (95% CI, 0.32 to 0.76) and false-positive rate of 0.03 (95% CI, 0.01 to 0.09). In the thoracic spine, the pooled sensitivity was 0.41 (95% CI, 0.14 to 0.74) and false-positive rate was 0.05 (95% CI, 0.02 to 0.09) (Lee, 2015).

The American Society of Neurophysiological Monitoring published a practice guideline for monitoring of segmental spinal nerve root function that addressed electronically-triggered electromyography monitoring of pedicle screw placement. This guideline states that the use of electrical stimulation to help determine correct placement of spinal pedicle screws is of value for determining appropriate screw placement. This was a Type C recommendation based on strong consensus and evidence provided by expert opinion, case reports, and nonrandomized comparative studies with historical controls (Leppanen, 2005).

Leon Jorba and colleagues (2025) published a prospective observational study of 81 individuals undergoing carotid endarterectomy to evaluate cranial nerve monitoring using corticobulbar motor evoked potentials, electromyography, and mapping techniques. Monitorability rates were 97.5% for the facial nerve, 90.1% for the vagus nerve, and 93.8% for the hypoglossal nerve. Using a 50% corticobulbar motor evoked potential decrease threshold, sensitivity was 0.82 and specificity was 0.95 for detecting postoperative cranial nerve injury. Permanent corticobulbar motor evoked potential changes occurred in 11 individuals (13.5%), with 9 individuals (11.1%) showing postoperative paresis. All deficits resolved within 1 year. Mapping identified functional atypical nerve branches anterior to the carotid axis in 8 cases (Leon Jorba, 2025).

Electroencephalography

Electroencephalography monitoring has been widely used to monitor cerebral ischemia secondary to carotid cross clamping during carotid endarterectomy. Electroencephalography monitoring may identify those individuals who would benefit from the use of a vascular shunt during the procedure to restore adequate cerebral perfusion. Conversely, shunts, which have an associated risk of iatrogenic complications, may be avoided in those individuals in whom the electroencephalogram is normal. Similarly, electroencephalography can be used in aneurysm clipping and other procedures where cerebral ischemia is a foreseeable risk. In cases with motor evoked potential stimulation, electroencephalography is sometimes used to monitor for complications such as seizures due to the electrical brain stimulation.

Electrocorticography and Direct Cortical Stimulation

Electrocorticography and direct cortical stimulation are used to define the area of surgical resection.

Electrocorticography is a recording of the electroencephalogram directly from a surgically exposed cerebral cortex, typically used to define the sensory cortex and to map the critical limits of a surgical resection. Electrocorticography recordings have been most frequently used to identify epileptogenic regions for resection. Direct cortical stimulation is used in craniotomies to help identify the functional cortex, most commonly for language and motor cortex or subcortical structures. Stimulation is delivered to each area to define where cortical function is disrupted so that key functional areas are avoided during resection.

A systematic review identified seven studies comparing electrocorticography-guided surgery and lesionectomy in individuals with medically refractory epilepsy associated with low-grade supratentorial intra-axial neoplasia, all with at least 12 months of follow-up. In pooled analysis, electrocorticography-guided surgery was associated with significantly greater postoperative seizure freedom (OR, 3.95; 95% CI, 2.32 to 6.72) than lesionectomy, with 85% in the electrocorticography-guided surgery group and 56% in the lesionectomy group achieving seizure freedom at follow-up (Warsi, 2023).

Visual Evoked Potentials

Visual evoked potentials are used to track visual signals from the retina to the occipital cortex and have been used for surgery on lesions near the optic chiasm. However, visual evoked potentials are very difficult to interpret during surgery due to their sensitivity to anesthesia, temperature, and blood pressure.

A 2021 systematic review of studies by Jashek-Ahmed (2021) evaluating visual evoked potential monitoring in individuals undergoing transsphenoidal surgery for pituitary adenoma identified 11 relevant studies, of which 10 were case series and 1 was a cohort study. The sensitivity of visual evoked potentials in predicting visual function outcome, reported for 3 studies, was 25%, 88%, and 100%, respectively. Specificity, reported in 7 studies, ranged from 85% to 100%. No operative complications related to intraoperative visual evoked potential monitoring were identified in the studies.

Vestibular Evoked Myogenic Potentials

The vestibular evoked myogenic potential is a biphasic response elicited by loud clicks or tone bursts recorded from the tonically contracted sternocleidomastoid muscle, suggesting that it is a vestibulocollic reflex whose afferent limb arises from acoustically sensitive cells in the saccule with signals conducted via the inferior vestibular nerve (Zhou, 2004).

In 2017, the AAN published a practice guideline for cervical and ocular vestibular evoked myogenic potential testing based on a review of nine controlled nonrandomized studies. The guideline panel stated that cervical or ocular vestibular evoked myogenic potential testing is possibly useful for distinguishing individuals with superior canal dehiscence syndrome. They also stated that evidence is insufficient to determine whether VEMP is useful for diagnosing vestibular neuritis or Ménière disease, and that it has not been demonstrated to be useful for diagnosing or managing vestibular migraine. There were no recommendations related to intraoperative use of vestibular evoked myogenic potentials (Fife, 2017).

Risk Stratification and Individual Selection

The evidence supports differential clinical utility of intraoperative neurophysiological monitoring based on individual risk factors and surgical complexity. The 2024 AO Spine/PRAXIS guideline explicitly limited its strong recommendation for monitoring to high-risk individuals, reflecting the guideline development group’s consensus that the balance of benefits and harms favors monitoring in this population. The high-risk designation encompasses individuals with complex deformity, myelopathy, cord compression, intramedullary tumors, unstable fractures, and ossification of the posterior longitudinal ligament with severe cord compression (Fehlings, 2024).

The risk-stratified analysis by Zhang and colleagues (2025) provides empirical support for this approach in cervical stenosis surgery. The substantially higher positive predictive value in the high-risk group (90.6%) compared to the low-risk group (40.74%) indicates that the clinical yield of monitoring alarms differs markedly based on preoperative characteristics. In the high-risk group, a monitoring alarm was highly likely to reflect true neurological compromise, whereas the majority of alarms in the low-risk group did not correspond to postoperative deficit. The finding that alarm reversibility, rather than preoperative risk factors alone, was the principal predictor of 6-month neurological improvement underscores the value of real-time monitoring in guiding intraoperative decision-making for appropriately selected individuals.

Utilization Patterns and Practice Variation

Contemporary database studies have characterized national trends in intraoperative neurophysiological monitoring utilization and identified substantial variation across institutions and populations. Al-Salahat and colleagues (2025) analyzed National Inpatient Sample data from 2008 to 2021 and found that neurophysiological monitoring utilization for spinal procedures increased from 5.14% to 29.62%, while monitoring during craniotomy procedures increased from 2.12% to 6.28%. The study identified disparities in monitoring access, with Black individuals having adjusted OR of 0.87 (95% CI, 0.77 to 0.99) and Hispanic individuals having adjusted OR of 0.88 (95% CI, 0.78 to 1.00) compared to White individuals for craniotomy procedures. For spinal procedures, individuals in the lowest income quartile had adjusted OR of 0.83 (95% CI, 0.80 to 0.86) compared to the highest quartile (Al-Salahat, 2025).

Lozano (2025) analyzed National Inpatient Sample data on 144,769 admissions for degenerative cervical myelopathy surgery from 2016 to 2022 and found overall monitoring utilization of 29%, increasing from 23% in 2016 to 34% in 2022. Utilization was lower among Medicare recipients (OR, 0.93; 95% CI, 0.90 to 0.97), among Medicaid recipients (OR, 0.91; 95% CI, 0.86 to 0.96), and among individuals in the lowest income quartile (OR, 0.83; 95% CI, 0.78 to 0.88) compared to respective reference groups. Individuals at government-owned hospitals (OR, 0.76; 95% CI, 0.66 to 0.87) or not-for-profit hospitals (OR, 0.81; 95% CI, 0.74 to 0.88) had lower odds of receiving monitoring compared to private investor-owned facilities. The median OR for between-hospital variation was 3.04, indicating that an individual undergoing surgery at one hospital could have over three times the odds of receiving monitoring compared to an individual at another hospital, independent of captured clinical factors. Measured individual, procedural, and hospital covariates explained only 4.7% of the variance in monitoring utilization (Lozano, 2025).

Rowe (2025) analyzed 285,939 individuals with cervical myelopathy or radiculopathy undergoing anterior cervical discectomy and fusion from 2011 to 2021 using the PearlDiver database. Monitoring utilization increased from 14.3% to 19.7%, reversing a declining trend observed in earlier studies. Combined somatosensory evoked potential and motor evoked potential monitoring was used in 59.9% of monitored cases, somatosensory evoked potentials alone in 34.2%, and motor evoked potentials alone in 1.3%. Regional variation was observed, with utilization highest in the Northeast (21.2%) and lowest in the West (14.2%). Thirty-day neurological complications were 0.09% with monitoring compared to 0.07% without monitoring, a difference that was not statistically significant (p=0.29). The very low baseline neurological injury rate (approximately 0.1%) after anterior cervical discectomy and fusion limits the ability to detect protective effects of monitoring in this population (Rowe, 2025).

Auditory evoked potential: Evoked potentials generated in the central nervous system by sound.

Brainstem auditory evoked potentials (BAEPs): Evoked potentials measured in the brainstem in response to sound.

Electrocorticography (ECoG): Direct measurement of the electrical activity of the brain using electrodes placed on the cortex.

Electroencephalogram (EEG): Measurement of the electrical activity of the brain.

Electromyogram (EMG): Measurement of electrical activity in muscle that has been electrically or neurologically stimulated.

Evoked potentials: Electrical activity evoked in one part of the nervous system through stimulation of another part of the nervous system.

Direct cortical stimulation: Application of stimulation directly to a surgically-exposed cortex.

Intraoperative: Occurring or performed during a surgical operation.

Motor evoked potentials (MEP): Electrical activity measurable in muscle in response to stimulation of the motor cortex area corresponding to that muscle.

Nerve conduction velocity test: Measurement of the speed at which a nerve impulse travels along a nerve following stimulation.

Somatosensory-evoked potentials (SSEP): Evoked potentials generated in the central nervous system by stimulation of peripheral sensory nerves.

Vestibular evoked myogenic potential (VEMP): Electrical activity in muscle (sternocleidomastoid for the cervical VEMP; inferior oblique for the ocular VEMP) generated in response to stimulation of the inner ear by sound.

Visual evoked potential (VEP): Evoked potentials generated in the central nervous system in response to light stimulus.

Peer-Reviewed Publications:

1. Al-Salahat K, Mohammad A, Suleiman A, et al. Trends and demographic disparities in the utilization of intraoperative neuromonitoring in the United States, 2008 to 2021. J Clin Neurophysiol. 2025; 42(4):e238-e245.
2. Azad TD, Pendharkar AV, Nguyen V, et al. Diagnostic utility of intraoperative neurophysiological monitoring for intramedullary spinal cord tumors: systematic review and meta-analysis. Clin Spine Surg. 2018; 31(3):112-119.
3. Hudson M, Esposito S, Zaki MM, et al. Intraoperative neurophysiological monitoring in full-endoscopic cervical endoscopic unilateral laminotomy for bilateral decompression. J Clin Med. 2026; 15(1):327.
4. Jashek-Ahmed F, Cabrilo I, Bal J, et al. Intraoperative monitoring of visual evoked potentials in patients undergoing transsphenoidal surgery for pituitary adenoma: a systematic review. BMC Neurol. 2021; 21(1):287.
5. Lee CH, Kim HW, Kim HR, et al. Can triggered electromyography thresholds assure accurate pedicle screw placements? A systematic review and meta-analysis of diagnostic test accuracy. Clin Neurophysiol. 2015; 126(10):2019-2025.
6. Leon Jorba A, Velescu A, Alvarez Lopez-Herrero N, et al. Early detection of cranial nerve dysfunction during carotid endarterectomy through intraoperative neurophysiological monitoring. Clin Neurophysiol. 2025; 172:10-16.
7. Lozano CS, Karthikeyan V, Shakil H, et al. Patient, hospital and geographic factors associated with intraoperative neuromonitoring for cervical spine surgery: a national analysis. Spine. 2025; Publish Ahead of Print.
8. Nwachuku EL, Balzer JR, Yabes JG, et al. Diagnostic value of somatosensory evoked potential changes during carotid endarterectomy: a systematic review and meta-analysis. JAMA Neurol. 2015; 72(1):73-80.
9. Reddy RP, Chang R, Rosario BP, et al. What is the predictive value of intraoperative somatosensory evoked potential monitoring for postoperative neurological deficit in cervical spine surgery? A meta-analysis. Spine J. 2021; 21(4):555-570.
10. Reddy RP, Singh-Varma A, Chang R, et al. Transcranial motor evoked potentials as a predictive modality for postoperative deficit in cervical spine decompression surgery: a systematic review and meta-analysis. Global Spine J. 2024; 14(5):1609-1628.
11. Rowe DG, Barrett C, Owolo E, et al. The prevalence of intraoperative neuromonitoring in anterior cervical discectomy and fusion: trends, variances, and value appraisal. Clin Spine Surg. 2025; 38(5):E283-E288.
12. Seidel K, Wagner N, Wermelinger J, et al. Motor evoked potential monitoring and continuous dynamic mapping: warning criteria during surgery on motor eloquent intra-axial brain tumors. Clin Neurophysiol. 2025; 178:2110979.
13. Tanaka Y, Kawaguchi M, Noguchi Y, et al. Systematic review of motor evoked potentials monitoring during thoracic and thoracoabdominal aortic aneurysm open repair surgery: a diagnostic meta-analysis. J Anesth. 2016; 30(6):1037-1050.
14. Thirumala PD, Crammond DJ, Loke YK, et al. Diagnostic accuracy of motor evoked potentials to detect neurological deficit during idiopathic scoliosis correction: a systematic review. J Neurosurg Spine. 2017; 26(3):374-383.
15. Thirumala PD, Udesh R, Muralidharan A, et al. Diagnostic value of somatosensory-evoked potential monitoring during cerebral aneurysm clipping: a systematic review. World Neurosurg. 2016; 89:672-680.
16. Warsi NM, Mohammad AH, Zhang F, et al. Electrocorticography guided resection enhances postoperative seizure freedom in low-grade tumor-associated epilepsy: a systematic review and meta-analysis. Neurosurgery. 2023; 92(1):18-26.
17. Zhang Y, Li J, Yuan Y, et al. The application value of intraoperative neurophysiological monitoring in cervical spinal canal stenosis decompression surgery. Spine J. 2025; 25:2026-2035.
18. Zhou G, Cox LC. Vestibular evoked myogenic potentials: history and overview. Am J Audiol. 2004; 13(2):135-143.

Government Agency, Medical Society, and Other Authoritative Publications:

1. American Academy of Neurology. Model coverage policy: principles of coding for intraoperative neurophysiologic monitoring (IOM) and testing. Approved 2010; Amended 2012; Procedure codes updated annually. Available at: https://www.aan.com/siteassets/home-page/tools-and-resources/practicing-neurologist--administrators/billing-and-coding/model-coverage-policies/18iommodelpolicy_tr.pdf. Accessed January 23, 2026.
2. American Association of Neurological Surgeons/Congress of Neurological Surgeons (AANS/CNS) Joint Section on Disorders of the Spine and Peripheral Nerves. Updated position statement: intraoperative electrophysiological monitoring. January 2018. Available at: https://spinesection.org/about/position-statements/. Accessed January 23, 2026.
3. Fehlings MG, Alvi MA, Evaniew N, et al. A clinical practice guideline for prevention, diagnosis and management of intraoperative spinal cord injury: recommendations for use of intraoperative neuromonitoring and for the use of preoperative and intraoperative protocols for patients undergoing spine surgery. Global Spine J. 2024; 14(3S):212S-222S.
4. Fife TD, Colebatch JG, Kerber KA, et al. Practice guideline: cervical and ocular vestibular evoked myogenic potential testing: report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology. Neurology. 2017; 89(22):2288-2296.
5. Leppanen RE. Intraoperative monitoring of segmental spinal nerve root function with free-run and electrically triggered electromyography and spinal cord function with reflexes and F-responses. A position statement by the American Society of Neurophysiological Monitoring. J Clin Monit Comput. 2005; 19(6):437-461.
6. Macdonald DB, Skinner S, Shils J, et al. American Society of Neurophysiological Monitoring. Intraoperative motor evoked potential monitoring: a position statement by the American Society of Neurophysiological Monitoring. Clin Neurophysiol. 2013; 124(12):2291-2316.
7. Martin WH, Stecker MM. ASNM position statement: intraoperative monitoring of auditory evoked potentials. J Clin Monit Comput. 2008; 22(1):75-85.
8. Nuwer MR, Emerson RG, Galloway G, et al. Evidence-based guideline update: intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology and the American Clinical Neurophysiology Society. Neurology. 2012; 78(8):585-589.
9. Toleikis JR, Pace C, Jahangiri FR, et al. Intraoperative somatosensory evoked potential (SEP) monitoring: an updated position statement by the American Society of Neurophysiological Monitoring. J Clin Monit Comput. 2024; 38(5):1003-1042.

1. American Academy of Neurological Surgery (AANS). Available at: https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments. Accessed January 23, 2026.

Brainstem Auditory-Evoked Potentials
Direct Cortical Stimulation
Evoked Response Studies
Motor-Evoked Potential Monitoring
Somatosensory Evoked Potentials
Vestibular Evoked Myogenic Potentials
Visual Evoked Potentials

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