1. science
2. medicine
3. surgery

Indications and Benefits of
Intraoperative Monitoring
During Aneurysm Surgery
Laligam N. Sekhar, M.D., F.A.C.S
JJeffrey
ff
Slimp,
Sli
MD
Louis Kim, MD
D
Department
t
t off Neurosurgery
N
University of Washington
The Dream of Neurophysiologic
p y
g
Monitoring….
 An important Brain function can be reliably
monitored continuously during the operation
 Changes in this brain function are detected
rapidly and communicated to the surgeon
 The
Th surgeon changes
h
what
h th
he iis d
doing
i ,
which improves the outcome of the
operation
i
Pitfalls in this concept
 The relevant neural tracts, or nerves may not be reliably
measurable…
measurable
 Changes are not detected properly, or information is not
communicated in a timelyy manner
 Technical problems, or patient has a preexisting deficit
g
cannot modify
y anything
y
g which can improve
p
 The surgeon
the outcome
 There is inadequate cooperation between anesthesiologist,
surgeon and the neurophysiologist
surgeon,
Monitoring
g During
g Aneurysm
y
Surgery
 To detect changes in Somatosensory Evoked Potentials
(SEP), and Motor Evoked Potentials (MEP) during
temporary occlusion of arteries (ischemia)
 To allow Burst suppression during protracted temporary
p
occlusion ((Brain Protection)) : EEGs byy compressed
Spectral Array
 To have assurance about the patency of arteries once
blood flow has been resumed
 To make sure that important perforators have not been
occluded during aneurysm clipping
 CN Monitoring during lower posterior circulation aneurysms
Major Monitoring Modalities
 Common Monitoring Modalities:
MEP, SEP,
ABR (for Posterior Fossa operations)
Cranial Nerves 7,8, 10, 11, 12 – for Posterior Fossa Operations
EEG by Compressed Spectral Array
 Other Potential Modalities
Tissue Blood Flow
Microdialysate chemicals e.g Glutamate
Tissue Oxygen tension
Thermal property of blood vessels
Doppler flow of major vessels
SSEP Technique
 Stimulus Sites:
Median Nerve
Ulnar Nerve
Tibial Nerve
 Scalp Recording:
Tibial: Cz’ - Fz
Med/Uln: C3’
C3’–
– Fz, C4’C4’-Fz
 Peripheral Recording:
Erb’s Point
Abductor Hallucis
SSEP Stimulus Parameters
 Pulse Duration: 0.2 msec
 Stimulation Rate: 3.1 Hz
 Stimulus Amplitude: 25 mA at wrist, 50 mA at ankle or
lower if movement is problematic
Transcranial
Electrical Motor
Evoked MEPs
Stimulate:
Scalp overlying the motor
cortex
Record:
1 Compound Motor
1.
Action
Potential (CMAP) in
hands
and legs
2. Spinal cord (for cord
tumors)**
tumors)
Reflects activity in
corticospinal pathway
*
MEP Stimulus Parameters




Pulse Duration: 0.05 msec
Train of pulses: 22-7
Stimulus Amplitude: 100100-800 V
Parameters and responses may vary considerably
between patients, and even within the same procedure
 Preferred anesthesia: TIVA (propofol/narcotic) or
Desflurane only
Rationale For Monitoring MEP
MEP, SEP
 During ischemia, synaptic activity ceases
around 15 to 20 ml/minute of CBF
 Infarction occurs when flow drops below 10
ml/min.
l/ i after
ft a few
f
minutes
i t
 Caution….Large
g areas of brain are not
measured by these tests
 A normal MEP will not reflect activity of the
Supplementary motor area, or other
Eloquent areas
How Monitoring Can Help
Help…
 During microsurgery, temporary clips are applied
on arteries (or induced hypotension used)
 Changes in SEP
SEP, EEG may indicate ischemia
change may be immediate..severe ischemia
Gradual Mild tto Moderate
Gradual…
M d t iischemia
h i
 Surgeon May reverse the ischemia by
R
Removing
i ttemporary clip
li
Raising Blood Pressure to improve collateral flow
 Or preemptively Protect the Brain with : Burst
Suppression
During Bypass Procedures
Procedures…
 The patient is placed in Burst suppression
with Barbiturates and Propofol, to suppress
synaptic activity, and brain metabolic demand
 Blood Pressure may be normal
normal, or raised
20%, to improve collateral flow
 Heparin is administered intravenously, and
monitored by Activated Clotting Time
 Temporary Occlusion Time…<45 minutes
Tolerance to temporary Occlusion
 Depends on : Metabolic Demand – e.g burst
suppression
Collateral Circulation – induced
hypertension
Perforators Involved? e.g. M1 vs M2
 Basilar Artery may tolerate occlusion for 10 to 15
minutes, depending on age and collaterals
 Unruptured Aneurysm patients have much better
tolerance than SAH patients
When to report
p Changes
g in Evoked
Potentials ?
 Report as soon as a change is detected, but when it is
certain that there is a change
 Give the surgeon the freedom to act on the
information……i.e. report dubious changes as well
 Supervising Neurophysiologist must be alerted before
critical points of surgery
 It is important for the surgeon and anesthesiologist to be
aware off the significance
f
off changes
 It is important for the team to communicate well before,
during and after the Operation…
Operation
Case Examples
MCA Aneurysm,
Aneurysm Loss of SEP
 Right MCA aneurysm
 Temporary loss of SEP signal with clipping
clipping.
 Recovered with revision of clips
Left median n.
Loss
Left tibial n.
Right median n.
Right tibial n.
Intraoperative
p
Aneurysm
y
Rupture
p
Before Dura Opened
 Aneurysm ruptured intraoperatively before
dural opening at 16:10 hrs just after run 6
and prior to run 7 which was at 16:21 hrs
Left median n.
Left tibial n.
Right median n.
Right tibial n
Case 1: ICA
ICA--PCOM Aneurysm Clipping
 Patient was a 61 yo female, who presented with
severe headache, nausea, vomiting, and
obtundation.
g y was 1 day
y post a left
 At time of surgery
subarachnoid hemorrhage.
 She had a ventriculostomy to relieve pressure
from SAH with some improvement of symptoms
Angiogram showed a ruptured complex left internal carotid
artery--posterior communicating artery aneurysm.
artery
Aneurysm
ACHOR Artery
PCOM Artery
She was taken to OR for clipping of the ICA aneurysm
aneurysm.
Monitoring was done with
Median and tibial nerve SEPs
Thenar and abductor hallucis MEPs
EEG to monitor burst suppression
Monitoring findings:
No changes in SEPs
Monitoring findings:
No change in MEPs through to dura closure,
closure >15 min after clipping.
clipping
So far, so good, but the risk isn’t over.
Monitoring findings:
Cli was ki
Clip
kinking
ki th
the anterior
t i choroidal
h
id l artery,
t
which
hi h arises
i
from
f
the
th ICA and
d
perfuses the posterior limb of the internal capsule.
ACHR Artery
PCOM Artery
Focal change in right thenar MEPs occurred during dural closure.
Recovery following change and repositioning the clip.
Angiogram showed complete clipping of aneurysm
Preop
Postop
Clinical p
postoperative
p
findings:
g
No focal motor deficit of right hand
Developed hydrocephalus, requiring shunting
Slow recoveryy but at 3 months was fullyy ambulatoryy with near
normal strength in all extremities
Michel Lawton’s
Lawton s Patient
 A 5151-year
year--old women subarachnoid hemorrhage, and
basilar bifurcation aneurysm
 Temporary clipping produced no electrophysiological
changes
 But complete loss of MEPs in the right arm and leg
immediately following permanent aneurysm clipping
 Careful examination of the clips revealed a perforator
caught between the blades.
 The clip was repositioned, the perforator was released, and
the MEPs and SSEPs returned to baseline values
values.
 The patient recovered without neurological sequelae.
Quinones-Hinojosa A, Alam M, Lyon R, Yingling CD, Lawton MT,
Transcranial Motor Evoked potentials during Basilar Aneurysm Surgery,
Neuroosurgery 54:916-24, 2004
49/ F, RUPTURED Aneurysm, H/H 2, Fisher 2,
BA Ti
Tip An
A 8.6
8 6 width
idth X 7.7
7 7 width
idth X 55.6
6 hheight
i ht mm, N
Neck
k 5.6
5 6 mm
Basilar Tip Aneurysm Clipping
SSEP Changes (With No changes in MEPs )
During Basilar Tip Aneurysm Clipping
L Median N Stim
Hz
R Median N Stim
L Tibial N Stim
R Tibial N Stim 3.1
Dura opened
13 27 Temp
13:27
T
Clip
Cli
13:32 1st Perm Clip
13:38 2nd Perm
Clip; Change in
SSEPs
13:39 Temp Clip off
and
d SSEPs recover
C4’-Fz 50 msec
C3’-Fz 50 msec
Cz’-Fz 100 msec
Cz’-Fz 100 msec
N changes
No
h
iin MEP
MEPs
During Basilar Tip Aneurysm Clipping
Right Thenar
R Abductor Hallucis
Left Thenar
L Abductor Hallucis
D
Dura
opened
d
13:27 Temp Clip
p
13:32 1st Perm Clip
13:38 2nd Perm Clip;
(Change in SSEPs); No
change MEPs
13:39 Temp Clip off
(and SSEPs recover)
Postoperative Course Excellent; At 2 months, mRS 2
At home,, completely
p
y independent,
p
, ready
y to return to work
Normal MEPs despite
p Clip
p Kinking
g
the A2 (SMN syndrome)












43/woman
Ruptured ACOM aneurysm
Uneventful Clipping
Normal SEP, MEP during the case
Normal Doppler Flow, ICG Angiography not available
Patient awoke from surgery, moving all limbs symmetrically
Delayed Right Hemiparesis, progressed to Hemiplegia
Angiogram : A slight kink of the left A2 by the clip, delayed flow
Taken back to the OR and clip repositioned
Normal SEP, MEP during the second surgery as well
CT and MRI: Supplementary Motor Stroke
Outcome: Complete recovery after 2 months
Preoperative Angiogram
Postoperative Angio, showing kink,
reduced flow
D i Second
During
S
dS
Surgery, MEP
MEPs were recorded
d d and
dN
Normall
Postoperative Angio showing Normal A2 flow
MRI showing Premotor Stroke
Non Detection of Heubner’s Territoryy
Ischemia by MEP/SEP




58/F with Dissecting A1 aneurysm
Clip Reconstruction,
Reconstruction successful
No SEP or MEP changes during the case
Awoke with Hemiparesis, resolved
completely after 3 days
 MRI: Heubner’s territory Infarction
Non Detection of Heubner territory Ischemia
58/F, Dissecting
58/F
Di
ti A1
Aneurysm
Clip Reconstruction, No change
in SEP
SEP, or MEP
Heubner territory stroke; Transient
Hemiparesis for 3 days; Complete Recovery
The Evidence
Patient Outcome with SSEP
monitoring - Aneurysms

42 / 97 patients (30 MCA & 12 ICA aneurysms)
had changes in SEP after temporary occlusion
– 3 patients did not recover; had postoperative
Deficits
– 39 who recovered SEPs had no deficits
Mizoi K et al, Neurosurgery 33: 434
434--440, 1993
Outcome with SSEP monitoring
g–
Skull base Tumors
 244 procedures with SSEP monitoring
 Classification
–
–
–
–
T
Type
I:
I No
N change
h
Type II: Changes that revert to baseline
Type III: Changes that do not revert to baseline
Type IV: Complete flattening without improvement
 Conclusions: SSEP are very sensitive but not
specific to evaluate postoperative outcomes in
patients with Skull Base Tumors
Bejjani GK, Nora PC, Vera PL, Broemling L, Sekhar LN.
The predictive value of intraoperative somatosensory evoked
potential monitoring: review of 244 procedures. Neurosurgery 43:
491-498, 1998.
491-
Results Bejjani et al
Results,
Motor Evoked Potentials
 In 30 patients with BA Tip Aneurysms, MEPs and SEPs
were recorded continuously
 MEPs alone changed in 5/30
5/30, SEPs alone in1/30
in1/30, and both
changed in 4/30 patients
 Inpatients with simultaneous changes, MEP changes more
robust and occurred earlier than SEP
robust,
 EP changes occurred during temporary occlusion (6 /30),
permanent clipping (3/30), and retraction (1/30)
 In all patients, EPs returned to baseline after corrective
measures
 Conclusion: EPs are very important
important, MEPs more sensitive
than SEPs to perforator ischemia
Quinones-Hinojosa A
A, Alam M
M, Lyon R
R, Yingling CD,
CD Lawton MT,
MT
Transcranial Motor Evoked potentials during Basilar Aneurysm Surgery,
Neurosurgery 54:916-24, 2004
Future Applications
pp
of Neuro
Monitoring






Monitoring of Deep Brain Tracts
Microchemical Monitoring, using Microdialysis
Tissue O2 Monitoring
Ultrasonic Vascular Monitoring e
e.g:
g: TCDoppler
Thermal Monitoring of tissues exposed
Monitoring of the surgical team for fatigue, etc.
Seizures During MEP Monitoring
 During the years 20102010-2011 we had many cases
of intraoperative seizures apparently caused by
MEP monitoring
 The incidence declined dramatically after using
Phosphenytoin rather than Levetiracetam for
intraoperative seizure prophylaxis
 We have developed a protocol that patients with
Preoperative seizures will not have or have
minimal use of MEPs during intracranial surgery
Conclusions
 Neurophysiologic Monitoring is very Useful during
Aneurysm Surgery
 Further Correlative study of outcomes after EP Monitoring
for Aneurysm surgery is needed
 More monitoring modalities should be explored
 Both SEPs, and MEPs should be monitored
 EEG Monitoring
g is essential to induce Burst Suppression
pp
 MEPs may be more sensitive to perforator ischemia
 However, some instances of ischemia and stroke may be
missed by current monitoring techniques