We use a variety of surgery specific tests when performing intraoperative monitoring. These tests are designed to monitor the patient's at risk nerve structures throughout the entirety of the procedure making real time neural feedback available to the surgeon. The tests vary depending on the type of procedure being performed. The most common tests performed are listed below.
SSEP-Somatosensory Evoked Potentials
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Structures Monitored: The posterior sensory pathways of the spinal cord starting from the ends of the limbs running up the spine and to the brain.
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Surgeries Used On: Spinal, Cranial, Peripheral, and Vascular
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How the Test is Performed: Small amounts of current are applid at the patient's wrists and ankles using small sticky electrodes. The current causes the nerves to send electrical impulses along the sensory pathway all the way until it reaches the brain. Subdermal electrodes are placed along this nerve pathway recording how long it takes the electrical impulse to travel as well as the size of the impulse. Finally, the impulse is recorded by electrodes at it's final destination, the cortex (the outer, top portion of the brain).
TceMEP-Transcranial Electric Motor Evoked Potentials
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Structures Monitored: The anterior motor pathway of the spinal cord starting at the brain running down the spinal cord and out to the muslces of the arms and legs.
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Surgeries Used On: Spinal and Vascular
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How the Test is Performed: Small amounts of currect are applied by electrodes that are placed on the top of the head. The current then travels down the spinal cord and continues to the hands and the feet. This electrical impulse causes our muscles to contract and this contraction is read by electrodes that are placed on the appropriate muscle groups in the arms and legs.
TOF- Train of Four
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Structures Monitored: This test assesses how much muscle relaxant a patient has in their system and helps determine when the muscle relaxant has worn off.
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Surgeries Used On: Any procedure in which the IOM technician needs to read the patient's muscle activity in order to provide the surgeon with accurate information.
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How the Test is Performed: A surface electrode is place on one of the patient's nerves. Current is applied to this nerve causing a muscle contraction. This muscle contraction is read and recorded by a subdermal electrode placed on the muscle.
EMG- Electromyography
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Structures Monitored: Any muscle group that is innervated by at risk nerve roots.
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Surgeries Used On: Spine, ENT, Cranial, and Vacular
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How the Test is Performed: EMG is simply the recording of muscle activity (similar to how an EKG records heart activity). Electrodes are placed on appropriate muscles and all muscle activity is recorded.
tEMG-Triggered Electromyography
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Structures Monitored: Any muscle group that is innervated by at risk nerve roots.
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Surgeries Used On: Spine, ENT, Cranial
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How the Test is Performed: tEMG is the same as EMG with the only difference being how the nerve is stimulated (EMG its stimulated naturally; tEMG the nerve is stimulated with electrical current). This test is used to help with placement of screws during spine surgery, to help with identification of nerve roots, or to test a nerve's functionality.
EEG-Electroencephalography
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Structures Monitored: Brain Activity
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Surgeries Used On: Spinal, Cranial, Vascular
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How the Test is Performed: Recording electrodes are placed in various locations on the scalp. Electrodes continuously record electrical activity of the brain and therefore help identify changes in brain acitvity.
VEP-Visual Evoked Potential
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Structures Monitored: Optic Pathway/Optic Nerve
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Surgeries Used On: Various neurosurgical procedures
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How the Test is Performed: Several electrodes are placed on the occipital lobe. The eyes are stimulated by a flash of a pattern, when the eye sees this pattern it sends an impulse along the optic nerve, which is then recorded off the electrodes that were placed on the back of the head.
BAER-Brainstem Auditory Evoked Response
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Structures Monitored: The auditory pathway beginning at the outer ear, through the inner ear, up the brainstem, and then recorded at the cortex.
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Surgeries Used On: Cranial, ENT
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How the Test is Performed: The auditory pathway is stimulated with an audible click (either through an earphone or a speaker). This click stimulates the nerve responsible for hearing and the impulse travels throguh the ear, up the brainstem, and on to the outer part of the brain where it is recorded by electrodes that are placed on the scalp.
Cortical Mapping and Language Mapping
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Structures Monitored: Cortical mapping allows the doctor to identify specific areas of the brain (language, motor cortex, sensory cortex) by stimulating the brain with current and then observing the body's response.
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Surgeries Used On: Cranial
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How the Test is Performed: The doctor simulates certainareas of the brain and responses are either recorded off of limb muscle activity or off of patient language responses depending on the area of the brain that was stiulated. The doctor will then label the brain accordingly.
Phase Reversal
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Structures Monitored: Motor Cortex, Sensory Cortex, and the Central Gyrus
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Surgeries Used On: Any cranial case where it is necessary for the doctor to identify the location of the Central Gyrus.
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How the Test is Performed: A grid stip with 8 holes is placed along the brain in an anterior-posterior fashion over the motor cortex and the sensory cortex. The surgeon will stimulate the brain in each of the holes located along the grid strip with a probe. The IOM technician records the responses and by observing the response on the computer, they are able to determine when the surgeon has found the Central Gyrus.
