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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.  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 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, are typically stimulated, ulnar or tibial nerve, but in some situations the spinal cord may be stimulated directly. Recording is done either cortically or at the level of the spinal cord above the surgical procedure. Intra-operative 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 monitoring 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.
• Visual-evoked potentials (VEPs) are used to track visual signals from the retina to the occipital cortex light flashes. VEP monitoring has been used for surgery on lesions near the optic chiasm. However, VEPs are very difficult to interpret due to their sensitivity to anesthesia, temperature and blood pressure.  

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 type of monitoring involves stimulation to the motor cortex using a magnetic coil placed over the head. The electromagnetic energy induces an electrical current within the brain which in turn can stimulate the motor neurons. While there is ongoing research interest in the use of motor-evoked potentials to assess the integrity of the corticospinal tracts (which are not assessed using sensory-evoked potentials), this technique has not yet received U.S. Food and Drug Administration (FDA) approval.

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 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 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. See separate policy Electrocorticography 

Intra-operative monitoring of visual-evoked potentials is considered investigational.  

Due to the lack of FDA approval, intraoperative monitoring of motor-evoked potentials using transcranial magnetic stimulation is considered investigational.

Intraoperative EMG and nerve conduction velocity monitoring during surgery on the peripheral nerves is considered not medically necessary.

Intraoperative monitoring typically is done in the operating room (OR) by a technician, with a physician as a remote backup. In some ORs’ there is a central physician monitoring room, where a physician may simultaneously monitor several cases.

Intraoperative monitoring is considered reimbursable as a separate service only when a licensed physician, other than the operating surgeon, performs the monitoring while in attendance in the operating room throughout the procedure.

Investigative service is defined as the use of any treatment procedure, facility, equipment, drug, device, or supply not yet recognized by certifying boards and/or approving or licensing agencies or published peer review criteria as standard, effective medical practice for the treatment of the condition being treated and as such therefore is not considered medically necessary.

The coverage guidelines outlined in the Medical Policy Manual should not be used in lieu of the Member's specific benefit plan language.

3/2004: Code Reference section completed

2/6/2007: Policy reviewed, no changes

9/20/2007: Code Reference section updated. ICD-9 2007 revisions added to policy, ICD9 Procedure code 00.94 added for 10/01/2007 revisions.

10/02/2009: Coding Section updated to include coding rule information specific to CPT-4 code 95920. CPT-4 codes 95961 and 95962 removed from Covered Codes Table. ICD-9 Procedure code 04.19 removed from Covered Codes Table. ICD-9 Diagnosis codes 433.10, 433.11, 737.30- 737.34, 737.39, 737.43, and 754.2 removed from Covered Codes Table. Added verbiage, "* Some covered procedure codes have multiple descriptions. Coverage will only be made for covered codes when used for services outlined within the policy statement section." to the Covered Codes Section.

 06/21/2011:  Policy statement revised to state that motor-evoked potentials using transcranial electrical stimulation may be considered medically necessary, and motor-evoked potential using transcranial magnetic stimulation is investigational. The Policy Exceptions section was updated to add the following verbiage: "Federal Employee Program (FEP) Members Only:  Effective 03/10/11, intraoperative monitoring is considered reimbursable as a separate service only when a licensed healthcare practitioner, other than the operating surgeon, interprets the monitoring. The monitoring is performed by a healthcare practitioner or technician who is in attendance in the operating room throughout the procedure."

12/21/2012:  Added the following new 2013 CPT codes to the Code Reference section: 95940, 95941, and G0453.

Blue Cross Blue Shield Association policy # 7.01.58

The code(s) listed below are ONLY covered if the procedure is performed according to the "Policy" section of this document.

Covered Codes

This is not an all-inclusive list of non-covered procedure codes.

The code(s) listed below and ANY code not listed in the previous section are considered non-covered for this procedure.

Non-Covered Codes

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