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INTRAOPERATIVE MONITORING
DURING CAROTID
ENDARTERECTOMY (CEA)
Che’Patrick, REEG,EPT,CNIM
Introduction
Electrophysiological
monitoring during CEA has
proven to be extremely
beneficial in preventing
permanent neurological
deficits.
Intraoperative EEG
monitoring is the most
common choice for CEA
EEG provides a
quantitative measure for
the spontaneous electrical
activity of the brain.
CEA Facts
CEA - introduced in 1954 as a surgical procedure
designed to remove plaque material from an
occluded artery in the neck.
Plaque material is made up of cholesterol, calcium
and fibrous tissue.
If untreated, a blocked artery can cause a stroke.
Strokes are the third leading cause of deaths in
the United States.
NEJM (1991) - concludes that CEA is highly
beneficial to patients with recent TIAs and high
grade stenosis of greater then 70% of the ICA.
Understanding Our Arterial System
The brain receives blood
through four arteries:
a. The right and left
common carotid arteries.
b. The right and left
vertebral arteries.
The common carotids
bifurcate into:
- external carotid artery
(supplies face and skull
- internal carotid artery
(supplies the brain, no
branches outside cranium)
Carotid Circulation
The circle of Willis is a band of
arteries at the base of the
brain formed by the internal
and the basilar artery.
These arteries form a
complete ring which
effectively act as
anastomoses for each other
during cross clamping
In theory, if a communicating
artery becomes blocked,
blood can flow from another
part of the circle to ensure that
the brain is not compromised.
Basilar view of the Circle of
Willis
Atherosclerotic
plaque tends to
develop at the
bifurcation of ICA
and ECA (just
below the level of
the jaw)
arrow pointing to
bifurcation
Plaque material
Carotid Endarterectomy Surgery
CEA was developed to prevent cerebrovascular accidents or
TIAs
Clamping of the ICA in the neck to remove the plaque from
the blocked artery.
To avoid the risk of producing ischemia of the ipsilateral
hemisphere and a consequent deficit, techniques employed:
Intraoperative EEG monitoring
Somatosensory evoked potentials
Transcranial Doppler
CBF measurements
Internal carotid stump pressure
However, EEG is rapidly becoming the standard of care for
inpatients undergoing CEA because it is continuous, noninvasive, inexpensive and most importantly, it provides direct
feedback within seconds after carotid clamping that the brain
is adequately perfused and oxygenated.
Why are we monitoring?
EEG changes can occur 10-15 second after cross
clamping of the ipsilateral internal carotid artery
occur due to reduced cerebral perfusion as a
result of insufficient collateral circulation.
Most surgeons resort to shunting once changes
are reported,
After removal of clamp, slowing may persist for 2-3
minutes until arterial blood flow has been restored
to the carotid artery
Prior to surgical monitoring, surgeons would place
a bypass shunt around the atherosclerotic plaque,
which carried blood to the brain for oxygenation
Technical considerations
Use at least 19 electrodes (international 10-20 system) - covers major
vascular territories and allows overlap within the montage should an
electrode fail
Electrode application (vary depending on departmental policy):
disc electrodes with collodion, disposable sub-dermal needles or electrode
caps.
Patient arrives in laboratory to under go hook-up prior to entering the
operating room.
14 or more channels - allows simultaneous display of activity from a variety
of cortical areas.
Preoperative EEG baseline obtained during relaxed wakefulness should be
performed prior to surgery. Patients with an abnormal EEG are more likely
to show changes with cross-clamping of the ICA
Recording parameters:
HFF of 70 Hz, LFF 1.0 Hz (60 Hz notch filter may be necessary)
paper speed of at least 15 mm/second
Time To Put The Patient To Sleep
Effects of Anesthesia on EEG
Pharmacologic agents used for induction and
maintenance
Low doses: rhythmic beta activity (18-25 Hz) over
the anterior hemisphere (similar to a normal
awake and relaxed patients with eyes closed)
This beta increases in amplitude, widespread,
anterior maximum and rhythmic, activity (WAR)
In addition, intermittent delta waves may be seen
over the anterior hemisphere.
Other factors that can effect EEG
- lowering of PaC02 < 40 mm Hg
- decreased blood pressure
- hypothermia
- hypoxia
Surgical Procedure
Obtain baselines with patient awake
and eyes closed.
Anesthetic that provides minimal
adverse effects on CNS is preferable
Communicating with the anesthetist
to use agents that will not interfere
with the EEG recording is very
important. medications ready to use.
Just remind the anesthesiologist
“Not To Bolus”
Induction
Post induction, the EEG can demonstrate
generalized slowing, with a decrease in
voltage, or a burst suppression pattern.
Should this happen, alert the surgeon
immediately since you will not be able be
able to tell if a change has occurred from the
patient’s baseline when clamping occurs.
The surgeon can choose to proceed with the
surgery or wait until the bolus has worn off.
Keep in mind cerebral profusion can not
be determined with barbiturates on board.
Burst Suppression