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Anesthesia and Intraoperative

Neurological MonitoringDavid Ferson, M.D.

Department of AnesthesiologyDepartment of NeurosurgeryM. D. Anderson Cancer Center

Lecture Outline

� Neuroanatomy and neurophysiology

� Modern imaging and navigation techniques

� Anesthetic agents and their effects on neurological monitoring

� Future directions

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Modern Imaging - Tractography

Modern Imaging - Tractography

Preoperative Surgical Planning

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Constant current generator producing a train of square wave, biphasic pulses of 1 ms phase duration at frequency of 60 Hz.

Ojemann stimulator (bipolar electrode with 5mm spacing).

SSEPs and CMEPs

Upper extremity

Lower extremity

Intraoperative EP Monitoring Gold Standard for Functional Mapping

Childs Nerv Syst. 2002 Jul;18(6-7):264-87. Epub 2002 Jun 13.Intraoperative neurophysiological monitoring in pediatric neurosurgery: why, when, how?Sala F, Krzan MJ, Deletis V.

sensory

motor

Cortical Mapping

motor sensory

TIBIAL SSEP – KNEE STIMULATION

contact 1 contact 5

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motor sensory

TIBIAL SSEP – ANKLE STIMULATION

Childs Nerv Syst. 2002 Jul;18(6-7):264-87. Epub 2002 Jun 13.Intraoperative neurophysiological monitoring in pediatric neurosurgery: why, when, how?Sala F, Krzan MJ, Deletis V.

Anesthetic Agents� Intravenous

� Benzodiazepins [Midazolam]� Barbiturates [Sodium Thiopental]� Opiods [Morphine, Fentanyl, Sufentanil, Remifentanil ]� Propofol� Etomidate� Ketamine� Dexmetetomidine� Neuromuscular Blocking Agents (NMBA)

� Inhalational� Halogenated agents� Nitrous oxide

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Insensitive to Anesthetics/Insensitive to

NMBA

BAEP, D WAVES, ?SUBCORTICAL SSEP

Agent Notes

Inhalational agents Little effectHigh doses suppresses subcortical SSEP

Intravenous agents Little effect

Sensitive to Anesthetics/Sensitive to NMBA

CORTICAL SSEP, MUSCLE MEP

Agent Notes

Inhalational agents Reduce amplitude even at low doses, MEP> SSEP

Midazolam, Thiopental At low dose reduce MEP amplitudeAt moderate doses reduce SSEP amplitude

Propofol Slight reduction of MEP/SEP amplitude (dose dependent)

Opioids No significant affect

Ketamine, Etomidate

Dexmetetomidine

Increase amplitude

BAEP, Cortical (P25-N35) – no effect,� Amplitude median nerve P15-N20

NMBA Obliterate MEPLow dose may allow monitoring (TOF 2/4)

Sensitive to Anesthetics/Insensitive to

NMBACORTICAL SSEP

Agent Notes

Inhalational agents ProblematicRestricted to < 0.5 MACDesflurane and Sevoflurane better

Nitrous oxide ProblematicMay be combined with intravenous anesthetic

Midazolam, Thiopental Amplitude suppression (0.2 µg/kg)

Propofol, Thiopental Mild amplitude suppression

Opioids No significant affect

Ketamine, Etomidate

Dexmetetomidine

Increase amplitude

BAEP, Cortical (P25-N35) – no effect,

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Insensitive to Anesthetics/Sensitive to NMBA

EMG

Agent Notes

Inhalational agents Little effect

Intraveneous agents Little effect

NMBA Obliterate EMGLow dose may allow monitoring (TOF 2/4)

Anesthetic Paradigmsfor Neuromonitoring

SSEP Monitoring

Halogenated inhalational agents (<0.5 MAC)

Opioid (Remifentanil 0.05-2mcg/kg/min)

±Ketamine or EtomidateDexmetetomidine (0.1-0.7 mcg/kg/hr)

± NMBA

SSEP/MEP Monitoring

Propofol infusion (<150 mcg/kg/min)Dexmetetomidine (0.1-0.7 mcg/kg/hr)

Opioid (Remifentanil 0.05-2mcg/kg/min)

±Ketamine or etomidate

EMG Monitoring

Inhalational agent

Intravenous anesthetic agents

± NMBA (maintain at least TOF 2/4)

EEG Monitoring

Halogenated inhalational agents (<0.5 MAC)

Nitrous/narcotic technique

± NMBA

BAEP Monitoring

Inhalational agent

Intravenous anesthetic agents

Future Directions� New imaging techniques

� Intraoperative MRI

� Intraoperative Navigation

� Intraoperative stimulation and correlation of neurological function

� Great research opportunities

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Stereotactic and Functional Neurosurgery, 2009

THANK YOU