Cranial Nerve Monitoring


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  • CN I, II & VII are sensory only. All others have motor components.
  • MUAP – Free Run EMG Muscle fibers range from 10 in the eye muscles to 3000 in larger muscles like the gastronemius.
  • CMAP – Triggered EMG
  • Typical peaks: N1, N2, N3; P1, P2, P3
  • Rarefaction causes sudden excitation (ear drum moves away from ear).
  • Cranial Nerve Monitoring

    1. 1. Cranial Nerve Monitoring Brian Owens Minnesota Epilepsy Group
    2. 2. Cranial Nerves <ul><li>EMG is used to monitor all cranial nerves accept I,II & VIII. </li></ul><ul><li>II & VIII are monitored by evoked potentials. </li></ul><ul><li>No current method for monitoring of CN I. </li></ul>
    3. 3. EMG (Electromyography) <ul><li>EMG is the recording of electrical activity of muscle. </li></ul><ul><li>Free run EMG </li></ul><ul><ul><li>Monitor for irritation or injury </li></ul></ul><ul><li>Direct Stimulation </li></ul><ul><ul><li>Identify nerves </li></ul></ul><ul><ul><li>Test their integrity </li></ul></ul>
    4. 4. The Motor Unit <ul><li>A single motor neuron and all the muscle fibers it innervates. </li></ul><ul><li>Muscle fibers contract in response to action potentials from the neuron. </li></ul><ul><li>When all the fibers contract this is called a motor unit action potential (MUAP). </li></ul>
    5. 5. Compound Muscle Action Potential (CMAP) <ul><li>“ The summation of nearly synchronous muscle fiber action potentials recorded from a muscle, commonly produced by stimulation of the nerve supplying the muscle either directly or indirectly.” </li></ul><ul><li>-AAEM 2001 </li></ul>
    6. 6. Recording Methods <ul><li>Surface needle electrodes (most common) </li></ul><ul><li>Electrodes are placed subdermally over the muscle. </li></ul><ul><li>Can be placed in a monopolar or bipolar manner. </li></ul>
    7. 7. EMG Parameter Settings <ul><li>Bandpass: </li></ul><ul><ul><li>5Hz-5KHz </li></ul></ul><ul><li>Time base: </li></ul><ul><ul><li>250ms-1sec </li></ul></ul><ul><li>Sensitivity: </li></ul><ul><ul><li>50-100mV </li></ul></ul>
    8. 8. Direct nerve stimulation <ul><li>Bandpass: </li></ul><ul><ul><li>5Hz-5kHz </li></ul></ul><ul><li>Analysis time: </li></ul><ul><ul><li>15-20ms </li></ul></ul><ul><li>Intensity: 0.1mA-1mA </li></ul><ul><li>A threshold can be determined also for stim intensity. </li></ul>
    9. 9. EMG Intraoperative Interpretation <ul><li>Based primarily on the presence of activity and partially on pattern. </li></ul><ul><li>Free run EMG should be made audible for instant feedback to the Surgeon and Neurophysiologist. </li></ul>
    10. 10. EMG Alarm Criteria <ul><li>Sustained firing of high frequency train lasting for tens of seconds </li></ul><ul><li>Several large bursts of activity of complex morphology </li></ul><ul><li>Sudden bursts of high amplitude spikes followed by complete silence </li></ul>
    11. 11. EMG Examples Zouridakis, Papanicolaou, 2001 (a) Baseline EMG. Note the low amplitude background activity on ch2. (b) High amplitude spikes are present on ch3 indicating irritation of the nerve corresponding to that channel.
    12. 12. Anesthesia Requirements (EMG) <ul><li>No muscle relaxants after anesthetic induction. </li></ul><ul><li>Depth of relaxation should be verified & monitored. (Train of four) </li></ul><ul><li>4/4 twitches optimal. </li></ul><ul><li>Gases have little or no effect on EMG. </li></ul><ul><li>Often you may be recording other modalities, plan accordingly. </li></ul>
    13. 13. CN I (Olfactory) <ul><li>No current method for monitoring of the olfactory nerve. </li></ul><ul><li>In one study OEP’s, were recorded from the olfactory tract s/p craniotomy & stimulated from the olfactory mucosa. </li></ul>
    14. 14. CN II (Optic) <ul><li>Flash VEP’s used intraoperatively. </li></ul><ul><li>LED goggles used for stimulation. </li></ul><ul><li>Typically 3 negative peaks and 3 positive peaks. </li></ul><ul><li>Responses do not reproduce well in surgery. </li></ul><ul><li>Responses heavily affected by inhalational gases. </li></ul><ul><li>Not commonly performed. </li></ul>
    15. 15. CN III, IV, & VI <ul><li>Skull base tumor removal </li></ul><ul><li>Posterior fossa tumor removal </li></ul><ul><li>Clivus tumor removal </li></ul><ul><li>Use caution when placing needle electrodes near the eye. </li></ul>III – inferior rectus, inferior oblique IV – superior oblique VI – lateral rectus
    16. 16. CN V (Trigeminal) <ul><li>Skull base tumor removal </li></ul><ul><li>Microvascular decompression for trigeminal neuralgia </li></ul><ul><li>Clivus tumor removal </li></ul><ul><li>Large posteior foss tumor removal </li></ul><ul><li>Recorded from the masseter. </li></ul>
    17. 17. Masseter Muscle
    18. 18. CN VII (Facial Nerve) <ul><li>Acoustic neuroma removal </li></ul><ul><li>Skull base tumor removal  </li></ul><ul><li>Parotid gland tumor removal </li></ul><ul><li>Recorded from Obricularis Oris (lower branch) & Orbicularis Oculi (upper branch) </li></ul>
    19. 19. CN VII (Facial Nerve)
    20. 20. Orbicularis Oris, Oculi
    21. 21. CN VIII (Vestibular cochlear) <ul><li>Sensory Nerve </li></ul><ul><li>BAERs (Brainstem Auditory Evoked Potentials) used to test function of auditory nerve and pathways in the brain stem. </li></ul>
    22. 22. CN VIII – Surgical Procedures <ul><li>Skull based procedures </li></ul><ul><li>Acoustic Neuromas </li></ul><ul><li>Cerebello-pontine angle </li></ul><ul><li>Posterior fossa </li></ul>
    23. 23. CN VIII - Anesthesia <ul><li>No requirements. </li></ul><ul><li>Anesthetic agents generally have minimal or no effect on BAERs. </li></ul>
    24. 24. CN VII - Stimulation <ul><li>Auditory clicks delivered through foam ear inserts attached to an air tube. </li></ul><ul><li>Rarefaction is recommended for well defined peaks. </li></ul><ul><li>Intensity: 80dB – 100dB </li></ul><ul><li>Rate: 11.1Hz </li></ul><ul><li>Duration: 0.03 – 0.1 msec </li></ul><ul><li>Contralateral ear should be masked with a white noise 40dB less than stimulated ear. </li></ul>
    25. 25. CN VIII - Recording <ul><li>Bandpass: </li></ul><ul><ul><li>30-3000Hz </li></ul></ul><ul><li>Sensitivity: </li></ul><ul><ul><li>1uV </li></ul></ul><ul><li>Time base: </li></ul><ul><ul><li>10 -15msec </li></ul></ul><ul><li>Trials: </li></ul><ul><ul><li>1500-2000 </li></ul></ul>
    26. 26. CN VIII - Generators <ul><li>I - Auditory nerve </li></ul><ul><li>II - Cochlear nucleus </li></ul><ul><li>III - Superior olive </li></ul><ul><li>IV - Lateral lemnisci </li></ul><ul><li>V - Inferior colliculus </li></ul>
    27. 27. CN VIII - Interpretation <ul><li>Have baselines visible for comparison. </li></ul><ul><li>Correlate clinical hx, peripheral hearing loss may result in unclear or absent peaks. </li></ul><ul><li>BAERs are subcortical and therefore minimally affected by anesthesia. </li></ul><ul><li>The slightest changes in amplitude and latency can be significant. </li></ul><ul><li>Amplitude and latency of peaks I & V most important. </li></ul><ul><li>Interpeak latencies of I-III & III-V represent peripheral and central conduction time and are also critical. </li></ul>
    28. 28. CN IX <ul><li>Large posterior fossa tumor removal (acoustic neuroma) </li></ul><ul><li>Radical neck dissection </li></ul><ul><li>Recorded from soft palate or Stylopharyngeus muscle (dilates the pharynx for swallowing) </li></ul>
    29. 29. CN X (Vagus) <ul><li>Record from false vocal cords with needle electrodes </li></ul><ul><li>Or record from vocal cords with special wired endotracheal tube </li></ul>
    30. 30. CN XI (Spinal Accessory) <ul><li>Skull base tumor removal </li></ul><ul><li>Jugular foramen tumor removal </li></ul><ul><li>Record from Trapezius muscle </li></ul>
    31. 31. CN XII (Hypoglossal) <ul><li>Skull base tumor removal </li></ul><ul><li>Jugular foramen tumor removal </li></ul><ul><li>Large posterior fossa tumors </li></ul><ul><li>Radical neck disection </li></ul><ul><li>Recorded from the tongue </li></ul>