INTRAOPERATIVE NEUROPHYSIOLOGY AND NEUROMONITORING

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INTRAOPERATIVE NEUROPHYSIOLOGY AND
NEUROMONITORING

• Ramsis F. Ghaly, MD, FACS
• and
• Todd Sloan MD MBA PhD
• University of Colorado Health Science Center

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EEG MONITORING UNDER ANESTHESIA

• VISUAL DIAGRAM (COMPRESSED SPECTRAL ARRAY)
• ANALYSE (SPECTRA)
• COMPRESS AND SPPRESS
• SMOOTH
• (Delta Theta Alpha Beta in a diagram
  Time against Hz)
• NUMERICAL VALUES
• BIS

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Bispectral Index

• Set of features on EEG(bispectrum, etal) combined
  and correlated with regression to clinical exam.
• Bispectrum A measure of the level of phase
  coupling in a signal, as well as the power in the
  signal

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BISPECTRAL INDEX (BIS)

• DIGITALIZE RAW SURFACE EEG (15-30SEC) AND PROCESS
  FREQUENCY AND AMPLITUDE AND CORRELATE TO DEPTH OF
  ANESTHESIA
• 70-75 RECALL OF WORDS OR PICTURES DEPRESSED
• lt70 EXPLICIT RECALL SIGNIFICANTLY DEPRESSED
• 60-40 GENERAL ANESTHESIA
• 40-60 TARGET IF OPIODS USED AND 35 IF NO OPIODS
• TIVA, HEMODYNAMIC INSTABILITY TO REDUSE
  ANESTHETIC DOSAGES, SPEED RECOVERY, CLOSED-LOOP
  ANESTHESIA
• INTERFERENCE FROM EXTERNAL, MECHANICAL AND
  MUSCLE ACTIVITY
• SEIZURE SPIKE ERRONEOUS VALUES
• HYPNOTIC AGENTS MAY NOT HAVE LINEAR RELATIONSHIP
  e.g. N20, KETAMINE, OPIODS, ETOMIDATE

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ANESTHETIC EFFECTS ON EEG

• DRUG TYPE- DOSE-RELATED (DEPTH OF ANESTHESIA)
• AMPILTUDE-FREQUENCY-PATTERN- HEMISPHERIC SYMMETRY
• INTRAVENOUS AGENTS
• FAST ACTIVITY- SLOW HIGH VOLTAGE
• EPILEPTIFORM ACTIVITY (KETAMINE-METHOHEXITAL)
• INHALATIONAL AGENT (FAST-LOW)
• SUB-MAC FAST ACTIVITY (15-30Hz)
• 1 MAC 4-8 Hz - 1.5 MAC 1-4 Hz - 2-2.5MAC BURST
  SUPPRESSION
• SPIKE WAVE EEG (ENFLURANE)
• ISOLECTRIC EEG

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ANESTHETICS PRODUCING BURST SUPPRESSION

• BARBITURATE
• ETOMIDATE
• ISOFLURANE (2-2.5MAC)
• SEVOFLURANE
• DESFLURANE

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INTRAOPERATIVE EEG MONITORING

• BISPECTRAL ANALYSIS (BIS) BIS guided anesthesia
  demonstrated superiority in monitoring depth of
  anesthesia, minimize awareness under anesthesia,
  reduction in anesthetic utilization, guide
  delivery, fast awakening. Spectral Entropy, a
  measure of disorder in EEG activity, is being
  evaluated.

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FACTORS AFFECTING EEG

• HYPOXIA
• HYPOTENSION, ISCHEMIA (e.g.CEA)
• HYPOTHERMIA
• HYPO-AND HYPER-CARBIA
• BRAIN DEATH
• SURGERYUNTOWARD EVENTS
• CEA- CARDIOPULMONARY BYPASS-
• CEREBRAL ANEURYSM CLIPPING

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EVOKED POTENTIALS SSEP/SEP ABR/BAEP VEPMEP
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EVOKED POTENTIAL

• EVOKED STIMULUS (AUDITORY ABR/BAER-VISUAL
  VEP-SOMATOSENSORY MN/ULNAR/PTN/CUTANEOUS SSEP)
  EEG IS SPONTANEOUS
• TRAVELLING PATHWAY
• RESPONSE (CORTICAL- SUBCORTICAL-SPINAL) (NEAR
  FIELD LATE LATENCY ABR/SEP- FAR-FIELD BAER/SSEP
  SHORT LATENCY)
• EP CHALLANGES
• MINUTE POTENTIALS IN MICROVOLTS COMPARED TO EEG
  IN MV
• ELECTRICAL ARTIFACTS
• LENGTHY AND MULTIPLE SYNAPTIC TRACTS AND
  VULNERABILITY TO ANESTHETICS AND EXTERNAL FACTORS
• TECHNIQUE FOR REPRODUCIBILITY
• AVERAGING
• AMPLIFIER

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Posterior Tibial N. SSEP
Primary Sensory Cortex
Med. Lemniscus
Cervico-Medullary Junction
Spinal Cord
stimulus
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Auditory Brainstem Response
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VISUAL EVOKED POTENTIALS (VEPS)

• EYE GOGGLES AND OCCIPITAL ELECTRODES
• RETINA-OPTIC NERVE-OPTIC- MED. GENICULATE-OCCIPITA
  L CORTEX (VP 100)
• PITUITARY, SELLAR AND SUPRASELLAR SURGERIES
• VARIABLE AND VULNERABLE UNDER ANESTHESIA

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ANESTHETIC EFFECTS ON EPS

• LATENCY DELAY
• AMPLITUDE REDUCTION (EXCEPT ETOMIDATE AND
  KETAMINE)
• VARIABLE AMONG AGENTS
• WORSE IN INHALATIONAL AGENTS AND DOSE DEPENDANT
• ADDITIVE EFFECTS OF AGENTS
• VEPgtSEPgtBAER

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FACTORS AFFECTING EPS RECORDING UNDER ANESTHESIA

• HYPOTHERMIA
• HYPOXIA
• HYPOTENSION/ISCHEMIA
• ANESTHETIC AGENTS
• SURGICAL FACTORS INJURY-COMPRESSION- RETRACTION

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INTRAOPERATIVE MEP EMG INCLUDING CRANIAL NERVE
MONITORING
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ElectroMyoGraphy
SSEP cannot evaluate individual nerve roots

• Operative Monitoring
• Nerve irritation
• Nerve identification (stimulation)
• Pedicle screw testing
• Reflex testing
• (Motor evoked potentials)

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Methods for Cranial Nerve Monitoring

• II Optic sensory VEP
• III Oculomotor motorinferior rectus m
• IV Trochlear motor superior oblique m
• V Trigeminal motor masseter and/or
  temporalis m
• VI Abducens motor lateral rectus m
• VII Facial motor obicularis oculi and/or
  obicularis oris m
• VIII Auditory sensory ABR
• IX Glossopharyngeal motor posterior soft
  palate (stylopharygeus m)
• X Vagus motor vocal folds, cricothyroid m
• XI Spinal Accessory motor sternocleidomastoid
  m and/or trapezious m
• XII Hypoglossal motor tongue, genioglossus m

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Facial Nerve Monitoring
Bursts 100 msec
Neurotonic 30 sec
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Muscle relaxation is usually avoided in
monitoring spontaneous EMG (amplitude dec.)
cn 9,10,11,12
cn 10
cn 9,12
cn 3,4,6
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Which Nerves?

• Cervical
• C2, C3, C4 Trapezius, Sternocleidomastoid
• Spinal portion of the spinal accessory n.
• C5, C6 Biceps, Deltoid
• C6, C7 Flexor Carpi Radialis
• C8, T1 Abductor Pollicis Brevis, Abductor
• Digiti Minimi
• Thoracic
• T5, T6 Upper Rectus Abdominis
• T7, T8 Middle Rectus Abdominis
• T9, T10, T11 Lower Rectus Abdominis
• T12 Inferior Rectus Abdominis
• Lumbosacral
• L2, L3, L4 Vastus Medialis
• L4, L5, S1 Tibialis Anterior
• L5, S1 Peroneus longus
• Sacral
• S1, S2 Gastrocnemius
• S2, S3, S4 External anal sphincter

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Stimulator
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ANESTHETIC REGIMEN FOR INTRAOPERATIVE
NEUROPHYSIOLOGICAL MONITORING
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Anesthesia Components Analgesia and
Sedation/Amnesia

• Opioids
• Morphine
• Demerol
• Fentanyl
• Alfentanil
• Sufentanil
• Remifentanil

Ketamine Dexmeditomidine
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Fentanyl
Excellent drug, blocks pain in pathways not used
by IONM such that sedative drugs that do hamper
IOM can be kept at lower level
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Sufentanil Fentanyl
MEP
SSEP
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Ketamine

• Perspective
• Provides amnesia and analgesia
• Inexpensive as infusion in TIVA
• Problem of hallucinations
• Increases ICP with
  intracranial pathology
• May inc seizures

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Anesthesia ComponentsAnalgesia and
Sedation/Amnesia

• Barbiturates (thiopental, methohexitol)
• Benzodiazepines (midazolam)
• Propofol
• Etomidate
• Droperidol
• Ketamine
• Dexmeditomidine

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Propofol is the most common TIVA sedative
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Muscle Relaxation

• Paralysis ok during intubation and some other
  times (e.g. back incision)
• Full paralysis may be necessary to reduce EMG
  interference near recording electrodes
  ( e.g. SSEP cervical
  response, epidural or neural response)
• Full or partial paralysis may reduce patient
  movement with stimulation
• Partial paralysis may be acceptable for
  electrically stimulated pathways
• Absence of paralysis may be necessary with
  mechanical stimulation or with pathology

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Motor Evoked Responses Start with TIVA

•  - Induction with appropriate medications
  (limit barbiturates and benzodiazepines)
  Using short to intermediate acting
  relaxants
• Propofol 1-2 mg/kg
• Succinylcholine, vecuronium, rocuronium, etc.
• Basic maintenance with TIVA
• Propofol 120-140 mg/kg/min
• Sufentanil 0.3-0.5 ug/kg/hr
• Use EEG to guide propofol
• No nitrous oxide, No potent inhalational
• No muscle relaxation

Desflurane 3 inhaled (1/2 MAC) may be tolerated
in healthy patients
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Summary Effective Anesthesia

• Work with monitoring to develop an anesthetic
  plan based on monitor techniques used
• Start the case with the best anesthesia possible
  and begin monitoring (use a bite block!)
• Review the responses
• Liberalize or improve anesthesia
• Hold the physiology and anesthesia steady
• Develop an anesthesia
• protocol

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THANK YOU FOR LISTENING

• QUESTIONS?