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MONITORING OPERATIONS IN THE SKULL BASE CHAPTER VI
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Monitoring of cranial nerves in skull base operations: what to monitor? 1. Extraocular muscles 2. Facial muscles 3. Masseter muscle 4. Tongue 5. CNIX pharynx 6. CNX larynx 7. ABR 8. CAP from CNVIII and cochlear nucleus
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Monitoring other cranial motor nerves Extraocular muscles CN III CN IV CN VI Lower cranial nerves CN IX CN X CN XI CN XII
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Monitoring other cranial motor nerves Monitoring the facial nerve is a model for monitoring other cranial motor nerves
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How to activate the motor system? Electrical stimulation of motor nerves Magnetic stimulation of motor nerves Electrical stimulation of the motor cortex Magnetic stimulation of the motor cortex
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How to record the response? Recording of electromyographic (EMG) potentials Mechanical recordings of muscle contractions Recording of motor nerve CAP
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Recording of EMG potentials
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Recording muscle responses Muscle relaxants cannot be used
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MONITORING OTHER CRANIAL MOTOR NERVES EXTRAOCULAR MUSCLES CN III CNVI CNIV LOWER CRANIAL NERVES CNIX CNX CNXI CNXII
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Monitoring nerves that innervate extraocular muscles CN III, CN IV, CN VI
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Recording EMG potentials from extraocular muscles Using needle electrodes
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Recording from extraocular muscles: Place needle electrodes percutaneously so they come close to respective muscles Medial rectus for CNIII Lateral rectus for CNVI Superior oblique for CNIV
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EMG potentials recorded from extraocular muscles in response to electrical stimulation of respective cranial nerves intracranially
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Recording EMG potentials from extraocular muscles Using non-invasive electrodes
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Electrical stimulation of the oculomotor nerve (CN III) Middle rectus Lateral rectus Masseter
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Monitoring multiple systems simultaneously Extraocular muscles Facial muscles Masseter muscle Tongue Neck muscles BAEP VEP
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Typical placements of recording electrodes used in skull base operations Recording from extraocular muscles: Place needle electrodes percutaneously so they come close to respective muscles Medial rectus for CNIII Lateral rectus for CNVI Superior oblique for CNIV
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Monitoring other cranial motor nerves Lower cranial motor nerves CN IX, CN X, CN XI, CN XII
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FROM YINGLING
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Monitoring CN X can be done by placing recording electrodes in the vocal folds
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FROM YINGLING Monitoring CNX
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FROM YINGLING
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Auditory neuromonitoring Recording of auditory evoked potentials in operations in the posterior fossa
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Monitoring of ABR can detect manipulations of the brainstem before cardiovascular signs change
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Waveform analysis of the ABR provides information about the anatomical location of an injury
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Different conventions for display of BAEP
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NEURAL GENERATORS OF THE ABR: Peak I: distal auditory nerve Peak II: central auditory nerve Peak III: mainly cochlear nucleus Peak IV: unknown Peak V: termination of the lateral lemniscus in the contralateral inferior colliculus
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Waveform analysis of the BAEP provides information about the anatomical location of an injury PEAK III PEAK V Ipsilateral stimulation
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Contralateral stimulation Waveform analysis of the BAEP provides information about the anatomical location of an injury PEAK III PEAK V
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