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ANESTHESIA MONITORING FOR NEUROSURGERY

ANESTHESIA MONITORING FOR NEUROSURGERY. Mark Welliver CRNA, MS Assistant Professor. Cerebral Blood Supply. Circle of Willis. Dorsal Column Pathways & Spinocervical Tracts of Dorsal-Lemniscal system. Sensory signals transmitted via long ascending fiber tracts to thalmus and then cortex.

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ANESTHESIA MONITORING FOR NEUROSURGERY

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  1. ANESTHESIA MONITORING FOR NEUROSURGERY Mark Welliver CRNA, MS Assistant Professor

  2. Cerebral Blood Supply • Circle of Willis

  3. Dorsal Column Pathways &Spinocervical Tracts of Dorsal-Lemniscal system • Sensory signals transmitted via long ascending fiber tracts to thalmus and then cortex

  4. Ventral and Lateral Spinothalamic Tracts of Anterolateral Spinothalamic system • Sensory nerve fibers cross anterior commissure of spinal cord before ascending to brain

  5. Pyramidal Tract aka Corticospinal Tract • Major pathways for motor signal transmission from cerebral cortex to spinal cord

  6. Supra and Infratentorial • The Tentorium is a anatomical landmark for describing gross locations in the brain. • It is the location of a “tenting” in of the dura above the cerebellum

  7. Anesthetic Effects on Evoked Potentials • Latency- time from stimuli to response • Amplitude- intensity of response • Volatile anesthetics increase latency and decrease amplitude

  8. Evoked Potentials   Monitoring: A). Sensory evoked potential (EPs)   1) Somatosensory evoked potentials (SSEPs)   2) Brainstem Auditory Evoked Potential (BAEPs or BAERs)   3) Visual evoked potential B) Motor Evoked Potentials   C)EEG   D) BIS

  9. Somatosensory evoked potentials (SSEPs) • Low-voltage current applied to peripheral nerve. ie. median or post tibial. • The resulting evoked potential (nerve impulse) follows the sensory pathways to brain where the electroencephalogram records it’s delivery • Measures the intactness of Dorsal Column pathways • Useful during surgeries of: back, spinal cord, cerebral aneurysms, AV malformations, deliberate hypotension

  10. Somatosensory evoked potentials (SSEPs) • Important to have good baseline interpretation • Maintain pre-described limits of inhalation agents • Communicate any changes to anesthetic including intravenous agents for proper interpretation • Irreversible SSEP loss closely predicts motor deficits • 20% latency increase and up to 50% amplitude decrease usual acceptable • Maintain close communicate with electrophysiology monitor

  11. Brainstem Auditory Evoked Potential (BAEPs or BAERs) • Auditory signal transmitted to patient follow auditory pathways

  12. Visual Evoked Potential • Visual stimuli from flashing diodes in goggles measures intactness of visual pathways-Optic and Geniculocalcarine tracts. • Useful with transphenoidal and anterior fossa surgery

  13. Motor Evoked Potentials • Measures motor pathways- Pyramidal or Corticospinal Tract by cortical stimilation and measured motor responses • Most technically difficult to measure • Useful during significant back surgeries • May replace intra-op “wake up” test • Muscle relaxants obviously interfere • Most useful in conjunction with SSEPs

  14. Anesthetic Effects On Evoked Potentials • All inhalation agents increase latency and decrease amplitude in dose dependant fashion

  15. Brain Waves Alpha Awake, resting Busy thinking Beta (Geta) General Anesthesia Theta Deep sleep, (Geta) Delta

  16. Anesthetic Effects On EEG ga awake-induction-euphoria-excitation-sleep-surg.plane-deep alpha alpha beta alpha theta delta

  17. Bispectral Analysis BIS Monitoring Review “Conscious Monitoring” presentation semester one by Professor Hogan

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