The document discusses various techniques for intraoperative neurological monitoring during surgery, including EEG, SSEP, MEP, transcranial Doppler, and cerebral oximetry. EEG measures electrical brain activity and can detect changes related to ischemia, anesthesia effects, or other insults. SSEP uses electrical nerve stimulation to measure sensory pathway function from peripheral nerves to the brain. MEP assesses motor pathways by recording responses to transcranial electrical stimulation. Transcranial Doppler noninvasively measures cerebral blood flow velocity. Cerebral oximetry monitors tissue oxygen saturation in the brain. These techniques provide different but complementary information and are useful for detecting adverse neurological events during surgery.

1. Manu Jacob
Perfusionist
kmct mch

2.  EEG
 SSEP
 MEP
 Transcranial Doppler
 Cerebral Oximetry

3.  Electroencephalogram – surface
recordings of the summation of
excitatory and inhibitory postsynaptic
potentials generated by pyramidal cells
in cerebral cortex
 EEG:
 Measures electrical function of brain
 Indirectly measures blood flow
 Measures anesthetic effects

4.  EEG used to monitor for ischemia
 Avoid during critical periods of the case:
 Changing anesthetic technique
 Changing gas levels
 Administering boluses of medications that affect
EEG

5.  Alpha wave -- 8 – 13 Hz.
 Beta wave -- >13 Hz. (14 – 30 Hz.)
 Theta wave -- 4 – 7.5 Hz.
 Delta waves – 1 – 3.5 Hz.

7.  rhythmic, 8-13 Hz
 mostly on occipital lobe
 20-200 μV
 normal,
 relaxed awake rhythm with eyes closed

8.  irregular, 14-30 Hz
 mostly on temporal and frontal lobe
 mental activity
 excitement

9.  Cardiopulmonary bypass
 Theoretically beneficial
▪ Embolic events with cannulation
▪ Increased risk in patients with carotid disease
 Difficult to interpret EEG changes
▪ Alteration of arterial carbon dioxide tension
▪ Changes in blood pressure
▪ Hypothermia
▪ Hemodilution (anemia)

10.  Definition: electrical
activity generated in
response to sensory or
motor stimulus
 Stimulus given, then neural
response is recorded at
different points along
pathway
 Sensory evoked potential
 Latency – time from stimulus
to onset of SER
 Amplitude – voltage of
recorded response

11.  Sensory evoked potentials
 Somatosensory (SSEP)
 Auditory (BAEP)
 Visual (VEP)
 SSEP – produced by electrically stimulating a cranial
or peripheral nerve
 If peripheral n. stimulated – can record proximally along
entire tract (peripheral n., spinal cord, brainstem,
thalamus, cerebral cortex)
 As opposed to EEG, records subcortically

12.  Stimulation with fine
needle electrodes
 Stimulate median nerve –
signal travels anterograde
causing muscle twitch, also
travels retrograde up
sensory pathways along
dorsal columns all the way
to brain cortex

13.  Can measure the
electrophysiologic
response to nerve
stimulation all the way up
this pathway
 Monitor many waves
(representing different
nerves along pathway) and
localization of where the
neural pathway is
interrupted is possible

14.  Transcranial electrical
MEP monitoring
 Stimulating electrodes
placed on scalp overlying
motor cortex
 Application of electrical
current produces MEP
 Stimulus propagated
through descending
motor pathways

15.  Evoked responses may
be recorded:
 Spinal cord, peripheral
n., muscle itself

16.  MEPs very sensitive
to anesthetic agents
 Possibly due to
anesthetic depression
of anterior horn cells in
spinal cord
 Intravenous agents
produce significantly
less depression

17.  Direct, noninvasive
measurement of CBF
 Sound waves
transmitted through
thin temporal bone,
contact blood, are
reflected, and detected
 Most easily monitor
middle cerebral artery

18.  Does not measure actual blood flow but velocity
 Velocity often closely related to flow but two are not equivalent
 Surgical field may limit probe placement and
maintenance of proper position
 CPB
 Detect air or particulate emboli during cannulation,
during bypass, weaning from bypass, decannulation
 Significant data pending
 Detection of vasospasm (well-established)
 Smaller area – increase in velocity (>120cm/s)

19.  Measures oxygen saturation in the vascular bed of the
cerebral cortex
 Interrogates arterial, venous, capillary blood within field
 Derived saturation represents a tissue oxygen saturation measured
from these three compartments
 Unlike pulse oximetry (requires pulsatile blood), NIRS assess
the hemoglobin saturation of venous blood, which along
with capillary blood, composes approximately 90% of the
blood volume in tissues
 Believed to reflect the oxygen saturation of hemoglobin in
the post extraction compartment of any particular tissue
 Measures tissue oxygen saturation

20.  EEG is a useful modality for measuring
intraoperative cerebral perfusion
 SSEP offers the additional advantage of
measuring subcortical adverse events
 New techniques for neurological monitoring
are being developed which need to be further
evaluated and validated