Intraoperative neurophysiological monitoring uses recordings of the nervous system's electrical response to the stimulation of specific neural pathways (e.g., 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-46 Electroencephalography and Video Electroencephalographic Monitoring
• CG-MED-50 Visual, Somatosensory and Motor Evoked Potentials

Clinical Indications

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:

• The criteria above are not met; or
• Intraoperative neurophysiological monitoring of visual-evoked potentials; or
• Intraoperative neurophysiological vestibular evoked myogenic potential testing; or
• 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.

Coding

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:

CPT

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.

Discussion/General Information

Evoked response studies, when used during surgical procedures, monitor the nerves that are located at or pass through operative sites. The functional integrity of neurologic pathways is monitored for compromise due to significant ischemia or injury that might put the tested nerves or spinal cord at risk. Real-time intraoperative neurophysiological monitoring (IONM) can be performed with the data transmitted to an off-site monitoring center where a physician (e.g. neurophysiologist) provides interpretation and alerts the surgical team if the individual’s neurological status is compromised.

The American Academy of Neurology (AAN), in its Principles of