INDEX


	Somatosensory Evoked Potentials (SSEP) SSEP monitoring maybe necessary to provide information during surgical procedures when the spinal cord could be at risk of being manipulated such as during fixation and stabilization after trauma, resection of spinal cord tumors, spinal and neck fusions, or surgeries for correction of spinal deformities such as scoliosis.Utilizing SSEP monitoring as an indicator of brain ischemia is extremely important during procedures such as aneurysm clippings. Peripheral nerve potentials, a cervico-medullary response, and primary sensory cortex responses are recorded during SSEP monitoring allowing observation of the entire sensory (dorsal column) pathway. The peripheral nerve response can serve as an excellent tool in detecting ischemia during procedures such as Anterior Lumbar Interbody Fusions (ALIF). Peripheral nerve monitoring can also provide information during procedures when positioning is of concern. Monitoring SSEPs can also be a useful tool during surgical procedures when the brainstem is at risk. SSEPs can be recorded from the upper and/or lower extremities (typically stimulation of the ulnar and posterior nerves). SSEP is often monitored in conjunction with Electromyography (EMG), and Pedicle Screw Stimulation.
	TransCranial Motor Evoked Potentials (TcMEPs) During surgical procedures that could potentially cause injury or irritation to the motor pathways (ventral portion) of the spinal cord, TcMEP monitoring can be very beneficial. Transcranial stimulation of the motor cortex at the scalp allows the monitoring team to make assessments of physiological events that may otherwise go undetected. Myleographic potentials are recorded and observed throughout the procedure. Resections of spinal cord tumors could benefit from TcMEPs. Although particularly sensitive to anesthesia, TcMEPs are thought to be more reliable than SSEPs in many cases.
	Electromyography (EMG) Procedures that may cause mechanical traction or irritation to spinal and cranial nerves such as microvascular decompressions, interbody spinal and neck fusions, laminectomies, or foramenotomies may benefit from the monitoring of EMG activity. During these procedures the monitoring team continuously observes muscle groups of the extremities providing vital information to the surgical team that may prevent injury to the descending motor tracts of the spine. Monitoring SSEP only during spine surgery can overlook injury to the motor pathways. Cranial nerve EMG monitoring should always be apart of surgical procedures of the cerebellopontine angle, and should be monitored in conjunction with Brainstem Auditory Evoked Responses. Monitoring if cranial nerve V is optimal during trigeminal nerve decompression. Usually more than one nerve is at risk during skull base surgeries therefore making this type of monitoring crucial in preserving the anatomy. Properly identifying cranial nerves during certain procedures by stimulating with a handheld probe. In addition to visualizing the data, audio output is available to surgeon.
	Pedicle Screw Simulation Surgical procedures of the spine and neck requiring fixation and stabilization with pedicle screws would benefit from pedicle testing. Stimulating pedicle screws can provide vital information to the surgeon aiding in determining the proximity of the screw to nerve, as well detecting possible fractures of the pedicle itself. Protrusion of the screw beyond the cortical bone results in low electrical impedance between the bone and the nerve. Properly placed screws have high impedances. After placing screws, the surgeon stimulates the screw utilizing a handheld probe delivering a small electrical current. The supramaximal threshold is reported once a muscle action potential has been observed. Typically a threshold of 10ma or higher supports proper screw positioning. Pedicle screw testing has become a very useful tool in spine surgery.
	Brainstem Auditory Evoked Responses (BAERs) Auditory stimulation of cranial nerve VIII produces a sequence of early components that occur in the first 10-15msec of stimulation known as BAERs (Brainstem Auditory Evoked Responses). This neural activity may be necessary to monitor during procedures involving the posterior fossa. BAERs and are often combined with other forms of monitoring such as SSEPs. Cranial nerves V and VII are also commonly monitored with auditory stimulation. By measuring the conduction of the auditory nerve, BAERs can be minimize the complications of loss of hearing during surgery in which the nerve is being manipulated such as disections of acoustic neuromas and other types procedures requiring the retraction of the brainstem. Patients suffering from hearing loss may not benefit from BAER monitoring. Only minimal direct effects of anesthestic agents are seen in BAER monitoring.
	Electroencephalography (EEG) Vascular surgeries such as carotid endarterectomies are the most common indications for intraoperative monitoring of EEG. Correlates between regional cerebral blood flow and ipsilateral alterations have been observed. EEG monitoring may also be useful during cranial procedures such as tumor resections, and dissections of arterial venous malformations. During the clipping of intracranial aneurysms monitoring for the effect of temporary or permanent carotid artery occlusion may be necessary. Monitoring of temporary aneurysm clippings may also be useful. If cerebral protection with barbiturate coma is expected, EEG monitoring is a necessity. EEG alterations may be an early sign of recurrent bleeding or spasm with subarachnoid hemorrhage.