Intraoperative Neurophysiologic Monitoring

Intraoperative Neurophysiologic Monitoring

手术目的：

what is intraoperative neurophysiological monitoring?

1. Intraoperative neurophysiologic monitoring (IONM) is a technique that is directly aimed at reducing the risk of neurological deficits after operations 2. IONM is a technique that makes use of recordings of electrical potentials from the nervous system during surgical operations.

1. The use of IONM offers a possibility to detect injuries before they become so severe they cause deficits after the operation. 2. Introduction of IONM has reduced the risk of debilitating deficits such as muscle weakness, paralysis, hearing loss, and other loss of normal body functions.

Evoked potential [pə'tenʃ(ə)l] monitoring includes

• somatosensory evoked potentials (SSEP), • brainstem auditory evoked potentials (BAEP), • motor evoked potentials (MEP), • visual evoked potentials (VEP).

1. SKULL BASE SURGERY

• One of the first application of intraoperation neurophysiology was monitoring facial nerve function during acoustic neuroma resection , • a technique actually pioneered in the late 19th which came into widespread use during the 1980s.

BEAP

MEP

• The rates of anatomic and functional facial nerve preservation could be significantly increased by using intraoperative facial nerve monitorin ． • The prognosis is obviously improved by IFNM in the patients with acoustic neuromas

• Similar technique can be used to monitor other cranial motor nerves by appropriat placement of recording electrodes.

• Some techniques for monitoring sensory nerves such as: visual evoked potential which are an obviously means of monitoring optic nerve function, are notoriously unstable under anesthesia.

auditory brain stem respones(ABR) ABR can evaluate precisely cochlear ['kɔkliə] nerve function.

Case Study •

A patient with a medium-sized vestibular schwannoma expressed a strong desire that her hearing and facial function be preserved after surgery. Her surgeons suggested a suboccipital approach to the mass lesion.

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The seventh and eighth cranial nerves were continuously monitored using facial EMG and the auditory brainstem response (ABR). Following the craniotomy, surgeons used a device to retract the cerebellum in order to facilitate access to the tumor. The ABR deteriorated immediately, characterized by a rapid reduction in wave V amplitude and a shift in the absolute latency of nearly one millisecond . This dramatic change in auditory function was immediately reported by the audiologist in an effort to minimize permanent auditory nerve injury. The retractor was removed and then repositioned. The ABR gradually improved to near-baseline morphology and absolute values.

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The schwannoma was successfully resected, and postoperatively the patient was found to have hearing levels equal to the preoperative findings.

2. SPINAL CORD SURGERY

• SSEP has been the standard of intraoperative monitoring, with excellent ability to assess dorsal column and lateral sensory tract function; it probably also can detect changes in function of anterior motor tracts by stimulating mixed sensorimotor peripheral nerves.

•MEPs were developed to better the motor neurophysiological pathways.

Technique • MEPs are elicited by either electrical or magnetic stimulation of the motor cortex or the spinal cord. Recordings are obtained either as neurogenic potentials in the distal spinal cord or peripheral nerve, • Electrical stimulation also can be applied directly over the spinal cord when a laminectomy affords exposure proximal to the lesion in question. Distal neurogenic potentials then can be recorded. • Its use in combination with SSEP appears to improve the accuracy of monitoring spinal cord function.

3. ANEURYMS SURGERY

• Treatment of cerebral aneurysms carries risks of ischemia to structure downstream from the aneurysm. • The risk is particulary high for aneurysm of the posterior communicating or perforators supplying critical brain stem and thalamic structures

• Electroencephalogram (EEG) and SEP can be recorded from the same scalp electrodes by directing the signals to separate amplifiers with approriate filter settings. • Scalp EEG can also be used to monitor cerebral function during carotid or other vascular surgery

• The EEG is used to titrate the level of barbiturate to obtain a burst-suppression pattern ,in which periodes of soelectricity alternate with higheramplitude bursts. • A burst ratio of about 20% burst activity is adequate,more than this proviodes no further cerebral protective effect and will make it more difficult to extubate the patient after the procedure.

• For anterior cerebral or anterior communicating artery anuerysm ,posterior tibial nerve SEP should be used since the lower extremity somatosensory area is in the distal anterior cerebral artery. • For posterior communicating or basilar artery aneurysms,both upper and lower extremity SEP should be recorded since occlusion of perforating arteries into the brain stem or thalamus can affect either or both of these pathways.

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