Audiology or not?Intraoperative neuromonitoring

Audiology or not?Audiology or not?IntraoperativeIntraoperative neuromonitoringneuromonitoring

William Hal Martin, Ph.D.Oregon Hearing Research CenterOregon Health Science University

American Academy of AudiologySan Diego, 2010

Role of the Audiologist in the Role of the Audiologist in the Operating RoomOperating Room

Other than physicians, audiologistsare the only other professionals who are, by definition of scope-of-practice, qualified to perform and interpret intraoperative neurophysiological monitoring.

Intraoperative Intraoperative Neurophysiological MonitoringNeurophysiological Monitoring

Intraoperative – during a surgical

procedure

Neurophysiological – related to brain or

nerve function

Monitoring – continual testing and

interpreting results

What do we monitor?What do we monitor?

• Pathways

–– Ascending (sensory) systemsAscending (sensory) systems

–– Descending (motor) systemsDescending (motor) systems

How do we monitor?How do we monitor?

• Pathways

–– Stimulate one endStimulate one end

–– Record at the other endRecord at the other end

–– Identify changes along the Identify changes along the pathway due to the surgerypathway due to the surgery

Why do we monitor?Why do we monitor?

• To reduce surgically related mobidity and mortality

• To protect the brain, nerves and spinal cord

When do we monitor?When do we monitor?• Whenever the surgical team believes

that the brain or nerve pathways are at risk due to: –– The nature or extent of the diseaseThe nature or extent of the disease–– The complexity of the surgical The complexity of the surgical

approachapproach

Who does monitoring?Who does monitoring?• Technical – Trained to perform

modified electrodiagnostic tests during surgery

• Professional – Trained to interpret changes in responses

• Both – Trained to perform AND interpret tests in real time

ControversiesControversies

• “Remote” supervision–– tech in the room and interpretation tech in the room and interpretation

done elsewheredone elsewhere

• Surgeon interpretation–– Automated systems that require the Automated systems that require the

surgeon to interpret results while surgeon to interpret results while operatingoperating

MontioringMontioring ProceduresProcedures• Auditory brainstem responses• Electrocochleography• Cranial nerve electromyography• Somatosensory evoked potentials• Electromyography (EMG)• Electrocorticography• Electroencephalography (EEG)• Motor evoked potentials w/EMG

ProblemProblem

Hearing and brainstem function can be damaged during cerebello-pontine angle surgery

Site of DamageSite of Damage

•• CochleaCochlea

•• Cochlear NerveCochlear Nerve

•• Brainstem Auditory PathwayBrainstem Auditory Pathway

ProceduresProcedures

•• CPA Tumor resectionCPA Tumor resection•• Vestibular nerve sectionVestibular nerve section•• MicrovascularMicrovascular decompressiondecompression•• Aneurysm repairAneurysm repair•• AVM repairAVM repair

Techniques: Techniques: Electrocochleography (EcochG)Electrocochleography (EcochG)

•• Information about the cochlea (SP) and Information about the cochlea (SP) and distal cochlear nerve (Wave I)distal cochlear nerve (Wave I)

•• Recorded from ear canal, tympanic Recorded from ear canal, tympanic membrane or promontorymembrane or promontory

•• Large signalLarge signal

N1

-

Electrocochleogram

2 ms

TM-Cz

1 µV

Techniques:Techniques:Auditory nerve compound action Auditory nerve compound action

potentialspotentials

•• Information about the proximal cochlear Information about the proximal cochlear nerve at the root entry zonenerve at the root entry zone

•• Recorded from wick, silver ball or hook Recorded from wick, silver ball or hook electrode placed by surgeonelectrode placed by surgeon

•• Giant signal Giant signal

Inferior vestibular nerveSuperior vestibular nerve

Auditory nerve

VVIII

IXXXI

Lang, 1985

VIII

IXX

XI

N1

P1

–

2 ms

Compound Action Potential

5 µV

Techniques: Techniques: Auditory Brainstem ResponsesAuditory Brainstem Responses

•• Information about the auditory Information about the auditory pathway through the midbrainpathway through the midbrain

•• Recorded from scalpRecorded from scalp

•• Small signalSmall signal

Morest, 1975

Cz-M ipsilateral

I

II

IIIV

IV

IIIII

VIV

2 ms

Auditory Brainstem Response

+

Cz-M contralateral

200 nV

StrategyStrategy

•• Smaller tumors Smaller tumors -- save hearing YESsave hearing YESEcochG, ANEcochG, AN--CAP, ABR tumor sideCAP, ABR tumor side

•• Medium tumors Medium tumors -- save hearing ??save hearing ??EcochG, ABR both sidesEcochG, ABR both sides

•• Larger tumors Larger tumors -- save hearing NOsave hearing NOABR nonABR non--tumor sidetumor side

Techniques: Techniques: Auditory Brainstem ResponsesAuditory Brainstem Responses

•• Information about the auditory Information about the auditory pathway through the midbrainpathway through the midbrain

•• Recorded from scalpRecorded from scalp

•• Small signalSmall signal

Interpretation:Interpretation:Changes in ABRChanges in ABR

• ↑ III-V IPI = rostral, systemic changes

• ↑ I-III IPI = changes in auditory function

• III Amplitude ↓ = earliest ABR predictor of postop deafness

Interpretation:Interpretation:Changes in ANChanges in AN--CAPCAP

• Latency ↑ = stretch nerve

• Amplitude ↓ = compressed nerve

• Absent N1 = total conduction block

1.5 µV–

0 10 20 ms

N1

P1

Møller, 1995

Interpretation:Interpretation:Criteria for concernCriteria for concern

Any change beyond the test-retest variability within a case should be considered a cause for concern

Case study:Case study:Total conduction blockTotal conduction block

• 62 y.o. female

• 1.5 cm vestibular schwannoma in left IAC

• Vertigo, left side tinnitus, mild high-frequency hearing loss

• Normal word recognition normal ABR

• Hearing preservation high priority

Pre-operative

Nerve exposed

Drilling canal

Resecting tumor

EcochG 500 nV 200 nV1.2 µVAN-CAP ABR +––

Resecting tumor

Resecting tumor

Resecting tumor

Resecting tumor

20 ms0

V

N1

P1

N1

Prell et al. 2008

Examples of mechanically evoked facial nerve activity

Motor Cranial Nerve MonitoringMotorMotor Cranial Nerve MonitoringCranial Nerve Monitoring

• Recordings made from muscles

innervated by cranial nerves at-risk

• Direct stimulation of cranial nerves

for:

–– identificationidentification

–– testing function testing function

ElectromyographyElectromyography

Cranial Nerve VII: FacialCranial Nerve VII: Facial• Intracranial

–– CPA CPA tumor resections

–– MVDMVD–– Vestibular nerve Vestibular nerve

sectionsection

• Intratemporal– Facial Nerve

decompression– Mastoidectomy– Tympanoplasty– Cochlear implant– Translab approach – Labrynthectomy

The Human SpineThe Human Spine

• Magnificently designed structure

–– Form and function Form and function -- vertebraevertebrae

•• StructureStructure

•• StrengthStrength

•• FlexibilityFlexibility

•• ProtectionProtection

Normal Spinal Column

View from left View from back

Spinal DeformitiesSpinal Deformities

• Examples

––ScoliosisScoliosis

––KyphosisKyphosis

––SpondylolisthesisSpondylolisthesis

Scoliosis Normal

Spinal Cord MonitoringSpinal Cord MonitoringSpinal Cord Monitoring

• Spinal tumors

• Spinal trauma

• Spinal deformities

Intraoperative Monitoring:Somatosensory Evoked

Potentials

Intraoperative Monitoring:Intraoperative Monitoring:Somatosensory Evoked Somatosensory Evoked

PotentialsPotentials

Monitoring Recommendations

Monitoring Recommendations

• Median n. stimulation

––Spinal cord surgery above C8Spinal cord surgery above C8

• Posterior Tibial n. stimulation

––Spinal cord surgery below C8Spinal cord surgery below C8

• Monitors SENSORY pathways

Mechanically evoked EMGMechanically evoked EMG

• Continuous, real-time EMG monitoring

• Indicates nerve root stretching,

compression and irritation

• Provides surgeon with immediate

information about MOTOR pathways

Mechanically evoked EMG from anterior tibialis muscle during L5 root palpation

Motor evoked potentials Motor evoked potentials -- EMGEMG

• Stimulate scalp with current

• Record from muscle groups below

surgical level

• Note changes in MOTOR pathway

EMG recording electrodes

Pedicle Screw Stimulationwith EMG Monitoring

Pedicle Screw StimulationPedicle Screw Stimulationwith EMG Monitoringwith EMG Monitoring

What are pedicles?What are pedicles?

Pedicle ScrewsPedicle Screws

• Metal screws that are driven

through the pedicle into a vertebral

body from the posterior side

• Form anchors to connect rods and

plates to other vertebrae

Scoliosis Corrected

Preoperative Postoperative

Lateral wall breach

Stimulating probe

Cathode (-)

Pedicle Screw Stimulation

Pedicle screw

Current returnAnode (+)In muscle

Brain Tumor ResectionEpilepsy Surgery

Brain Tumor ResectionEpilepsy Surgery

Motor Strip MappingMotor Strip Mapping

• Variation of somatosensory evoked

potentials

• Stimulate nerves at the wrist

• Identifies motor and sensory areas

of the cerebral cortex

1

2

3

4

Motor Strip MappingMotor Strip Mapping

5

Functional Cortical MappingFunctional Cortical Mapping

• Stimulate cortex directly

• Record evoked movements

• Note changes in language function

ASHA Ad Hoc Committee on Advanced in Clinical PracticeNeurophysiologic Intraoperative Monitoring

It is the position of the American Speech-Language-Hearing Association (ASHA) that neurophysiologic intraoperativemonitoring is within the scope of practice of audiologists with the appropriate knowledge base and skills. The purpose of neurophysiologic intraoperative monitoring is to assist surgeons to minimize or avoid altogether the occurrence of intraoperativeinjury to neural structures at risk due to the nature of the pathology and their proximity to the surgical field.

The practice of neurophysiologic intraoperative monitoring by an audiologist requires knowledge in neuroanatomy and neurophysiology, with special emphasis in neurodiagnostictechniques and their intraoperative applications. In addition, familiarity with the surgical procedure, effects of surgical manipulations and pharmacologic agents on neurophysiologic events, and the ability to recognize those events also is required.

If practitioners choose to perform these procedures, indicators should be developed, as part of a continuous quality improvement process, to monitor and evaluate the appropriateness, efficacy, and safety of the procedure conducted.

“Audiologists administer and interpret electrophysiologic

measurements of neural function including, but not limited to,

sensory and motor evoked potentials, tests of nerve

conduction velocity, and electromyography. These

measurements are used in differential diagnosis, pre- and

postoperative evaluation of neural function, and

neurophysiologic intraoperative monitoring of central nervous

system, spinal cord, and cranial nerve function.”

AAA Response to the AMA Scope of Practice Data Series: Audiologists -October 2009

Proposed Wording (version 1.0) in Scope of Practice

Audiologists are trained to administer and interpret

electrophysiological measurements of neural function

following stimulation of the auditory and vestibular sensory

pathways. Additionally, audiologists are also trained in the

use of electrophysiological measures to assess facial nerve

function. These same techniques may be employed in the

operating room (OR), and Intensive Care Unit (ICU)

settings to assess the physiological integrity of related

nervous system structures.

These measurement techniques include but are not limited

to the auditory brainstem response (ABR),

electrocochleography (ECochG), direct VIIIth nerve

recordings and vestibular evoked myogenic potentials

(VEMP), auditory evoked potentials including the ABR, the

auditory middle latency response (AMLR) and auditory late

response (ALR) following electrical stimulation of the

auditory pathway ( in cochlear implant recipients, and

candidates), and neurophysiological evaluation of facial

nerve function.

In addition to these activities, audiologists may be engaged

in neurophysiological intraoperative monitoring efforts that

are designed to help preserve the physiological integrity of

motor cranial nerves (e.g., CN III, IV, V, VI, VII, IX, X, XI, XII)

that are at risk for damage during various neurosurgical and

neurotological surgeries.

It is not the intention of the Academy to limit IOM performed by audiologists to the above modalities, however, audiologists who are engaged in neurophysiological monitoring activities outside of those mentioned above, (e.g. spinal cord function monitoring, peripheral nerve monitoring, monitoring for Parkinson's d., cortical localization) are encouraged to seek credentialing either through local privileging (for medical centers and hospitals), or, from other professional societies that credential non-physician providers (e.g. American Board of Neurophysiological Monitoring), as the Academy as an organization is not considered to be qualified to assess knowledge and skills in those IOM procedures.

The future of audiology?The future of audiology?

Audiology TechAudiology Tech for a local medical group in the for a local medical group in the NW San Antonio area:NW San Antonio area:

The job duties includeThe job duties include::

Basic Basic AudiologicAudiologic testing to include: testing to include:

Pure Pure ToneAudiometryToneAudiometry, , TympanometryTympanometry, ,

Vestibular assessment and VEMP testing.Vestibular assessment and VEMP testing.

The future of audiology?The future of audiology?

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Training opportunities?Training opportunities?

American Societyof Neurophysiological Monitoring

www.asnm.org