What testing modalities are performed in intraoperative monitoring?

Many different modalities can be used in the OR. Frequently several modalities, such as SSEP, EMG and MEP (see below) are used together in the same surgery. Some of the most widely used modalities include:

• SSEP (Somatosensory Evoked Potentials)-the response recorded from the brain, nerve, or spinal cord to electrical stimulation of peripheral nerve. Used most often to monitor the integrity of the dorsal columns of the spinal cord during spine surgery; also used in some brain surgeries and peripheral nerve surgeries.

• TCeMEP ( Transcranial Electrical Motor Evoked Potentials): an electrical stimulus is applied to the motor cortex of the brain, and a response recorded from the spinal cord or from limb muscles. Works like SSEP (see above), but in the opposite direction, to monitor function of the motor tracs of the spinal cord.

• BSEP (Brainstem Auditory Evoked Potentials)-an electrical response, originating in the brainstem, to an auditory stimulus, usually a click delivered through small in-the-ear earphones. Used to monitor brainstem function and to help preserve hearing in acoustic neuroma and brainstem tumor cases. ·

• EMG (electromyography)-spontaneous EMG is used to detect incipient nerve damage in spine surgery (spinal nerve roots) and in skull base surgery (facial nerve and other cranial nerves). Evoked EMG, using an electrical stimulus delivered through a hand-held probe used by the surgeon, is also used to identify and test nervous structures.

• EEG (Electroencephalogram)-spontaneous brain activity is recorded to monitor functional integrity of the cerebral cortex, specifically to avoid injuries caused by ischemia (reduced blood flow) during carotid endarterectomies and aneurysm clippings.

• ECOG (Eiectrocorticography)-EEG recorded directly from the exposed surface of the brain to help define the borders of resection (tissue removal) in epilepsy surgeries and craniotomies for brain tumors.

• Direct Cortical Stimulation: Also used in epilepsy and tumor surgeries, to identify and map eloquent areas of the brain (speech and motor areas)

• TCD (Transcranial Doppler) blood flow velocity in the internal arteries of the brain is measured using an ultrasound beam, analogous to clocking a baseball pitch with a radar gun. Used to monitor cerebral blood flow in carotid endarterectomies.

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