Relaxants By Decade

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Neurophysiologic Monitoring
James E. Caldwell M.B.Ch.B. June 23 2004
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Outline of Presentation

• Electroencephalography (EEG)
• raw
• processed power, bispectral and entropy
  analysis
• Evoked responses
• sensory SSEP, BAEP, VEP
• motor motor evoked potential (MEP)
• direct nerve stimulation and electromyography
• Perfusion/Oxygenation Monitoring
• Transcranial Doppler
• Jugular bulb venous saturation
• near infra red spectroscopy
• intracerebral electrodes

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Encephalography
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The Standard EEG Montage
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The Standard EEG
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Normal Patterns of EEG Components
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The Standard EEG
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Processed EEGPower Spectral Array
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Processed EEGPower Spectral Array
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Processed EEGPower Spectral Edge
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Processed EEGBIS Monitor
100 - 80 Responds to normal voice 80 -
60 Responds to loud voice or shaking 60 -
40 Unresponsive low probability of recall 40 -
20 Deep hypnotic state 20 - 0 Burst suppression
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BIS and Lack of Awareness
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Processed EEGEntropy Monitor
Examines the randomness (entropy) of the EEG
signal. Increasing anesthetic depth is
associated with decreasing entropy. Takes into
account the surface EMG.
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Pathological Conditions and the EEG
Hypoxia/ischemia nonspecific slowing Hypotension
little effect until extreme Hypothermia
frequency and amplitude decrease EEG flat at 15
- 18 C Hyperventilation may produce seizures
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Anesthesia Drugs and the EEG
Subanesthetic doses can produce increased
frequency of EEG With increasing depth get slower
frequency, increased amplitude IV and vapor
anesthetics can abolish the EEG Ketamine produces
a disorganized EEG Methohexital and etomidate can
produce seizure-like activity Nitrous oxide
increases EEG frequency
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Intraoperative Use of the EEG
Raw EEG electrocortigography - seizure surgery
or awake craniotomy with mapping Processed EEG
monitoring brain function when ischemia is a risk
e.g carotid endarterectomy BIS monitor measure
of anesthetic depth? tool to aid in reduction of
anesthetic drugs given
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Evoked Responses
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Evoked Responses Sensory Motor Direct
nerve Brain mapping
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Sensory Evoked Potentials (SEP)
Somato-sensory evoked potential SSEP -
electrical stimulation of peripheral nerve and
detection of signal at points along the
neuraxis Brainstem auditory evoked potential
BAEP - aural stimulation by microphone in ear
canal Visual evoked potential VEP - flashes of
light to the eye rarely used
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Somato-Sensory Evoked PotentialsCharacterized
by direction and latencyUsed to test integrity
of spinal cord and sometimes brain function
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Sensory Evoked Potentials (SEP) 2
Brainstem auditory evoked potential BAEP - used
to test integrity of brainstem or auditory
apparatus very robust Visual evoked potential
VEP - used to test integrity of optic tracts,
very sensitive to anesthesia and unreliable
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Motor Evoked Potentials 1
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Motor Evoked Potentials 2
Transcranial stimulation of motor cortex Response
can be detected in cord, motor nerve or muscle
(EMG) Stimulation is usually electrical used to
be by magnetic pulse A variation is to stimulate
the cord directly More sensitive to anterior cord
function than SSEP
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Anesthetic Drugs and Evoked Potentials
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Direct Nerve Stimulation With EMG Response
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Direct Stimulation
Nerves or cortex are stimulated
directly Responses are electromyography, direct
observation of movement or effect on speech Motor
mapping for tumor or seizure focus
resection Speech mapping for tumor or seizure
focus resection Cranial nerve monitoring during
acoustic neuroma or parotid gland surgery Others
selective dorsal rhizotomy tethered cord
release pedicle screw placement
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Cerebello-Pontine Angle Tumor
Avoid muscle relaxants otherwise any anesthetic
is OK Can monitor all cranial nerves from seven
through twelve by EMG
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Perfusion/Oxygenation Monitoring
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Transcranial Doppler Ultrasonography
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Near Infrared Spectroscopy
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Jugular Bulb Venous SaturationEvidence of
insufficient oxygen delivery to brainSaturation
lt 50 is indicative of cerebral ischemia
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Intracerebral Electrodes
Microelectrodes and microcatheters in
experimental stages Can measure regional oxygen
tension, acid-base status and potentially energy
state Highly invasive and only experimental at
present
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Questions?
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Thank You