INTRAOPERATIVE NEUROPHYSIOLOGY AND NEUROMONITORING Ramsis F. Ghaly, MD, FACS and Todd Sloan MD MBA PhD University of Colorado Health Science Center

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

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

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 <70% 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

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

ANESTHETICS PRODUCING BURST SUPPRESSION BARBITURATE ETOMIDATE ISOFLURANE (2-2.5MAC) SEVOFLURANE DESFLURANE

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.

FACTORS AFFECTING EEG HYPOXIA HYPOTENSION, ISCHEMIA (e.g.CEA) HYPOTHERMIA HYPO-AND HYPER-CARBIA BRAIN DEATH SURGERY:UNTOWARD EVENTS CEA- CARDIOPULMONARY BYPASS- CEREBRAL ANEURYSM CLIPPING

EVOKED POTENTIALS SSEP/SEP ABR/BAEP VEP MEP

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

Posterior Tibial N. SSEP Primary Sensory Cortex Med. Lemniscus Cervico-Medullary Junction Spinal Cord stimulus

Auditory Brainstem Response

VISUAL EVOKED POTENTIALS (VEPS) EYE GOGGLES AND OCCIPITAL ELECTRODES RETINA-OPTIC NERVE-OPTIC- MED. GENICULATE-OCCIPITAL CORTEX (VP 100) PITUITARY, SELLAR AND SUPRASELLAR SURGERIES VARIABLE AND VULNERABLE UNDER ANESTHESIA

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 VEP>SEP>BAER

FACTORS AFFECTING EPS RECORDING UNDER ANESTHESIA HYPOTHERMIA HYPOXIA HYPOTENSION/ISCHEMIA ANESTHETIC AGENTS SURGICAL FACTORS: INJURY-COMPRESSION- RETRACTION

INTRAOPERATIVE MEP & EMG INCLUDING CRANIAL NERVE MONITORING

ElectroMyoGraphy SSEP cannot evaluate individual nerve roots Operative Monitoring Nerve irritation Nerve identification (stimulation) Pedicle screw testing Reflex testing (Motor evoked potentials)

Methods for Cranial Nerve Monitoring II Optic sensory: VEP III Oculomotor motor:inferior 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

Facial Nerve Monitoring Bursts 100 msec Neurotonic 30 sec

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

Which Nerves? Cervical Thoracic Lumbosacral Sacral 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

Stimulator

ANESTHETIC REGIMEN FOR INTRAOPERATIVE NEUROPHYSIOLOGICAL MONITORING

Anesthesia Components: Analgesia and Sedation/Amnesia Opioids Morphine Demerol Fentanyl Alfentanil Sufentanil Remifentanil Ketamine Dexmeditomidine

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

Sufentanil Fentanyl MEP SSEP

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

Anesthesia Components: Analgesia and Sedation/Amnesia Barbiturates (thiopental, methohexitol) Benzodiazepines (midazolam) Propofol Etomidate Droperidol [Ketamine] [Dexmeditomidine

Propofol is the most common TIVA sedative

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

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

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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