iom during carotid endarterectomy 2008

Intraoperative monitoringduring carotid endarterectomy

Intraoperative monitoringduring carotid endarterectomy

Dr.Tuan Tu Quoc Le(presented at Tuen Mun Hospital, Hong

Kong 2008)

BackgroundCEA is a surgical procedure designed to

prevent ischemic stroke by removing anatheromatous lesion at the carotid bifurcation& restoring the patency of the carotid vesselsto an almost normal levelBut: Stroke is the most feared complication of

carotid artery surgery, stroke rate ranges from2% to 7.5% (Sila,1998).CEA is recommended in patients with: 50–69% symptomatic stenosis provided that the rate of

stroke/ death is < 6%, 60–99% asymptomatic stenosis provided that the risk is < 3%

(Chaturvedi et al., 2005 ).

CEA is a surgical procedure designed toprevent ischemic stroke by removing anatheromatous lesion at the carotid bifurcation& restoring the patency of the carotid vesselsto an almost normal levelBut: Stroke is the most feared complication of

carotid artery surgery, stroke rate ranges from2% to 7.5% (Sila,1998).CEA is recommended in patients with: 50–69% symptomatic stenosis provided that the rate of

stroke/ death is < 6%, 60–99% asymptomatic stenosis provided that the risk is < 3%

(Chaturvedi et al., 2005 ).

Carotid endarterectomy

Mechanism Preventative methods Drawbacks of preventativemethods

IntraoperativeEmbolism Careful manipulation

Shunt avoidanceDuration of surgeryRisk of brain hypoperfusion

Hemodynamic Shunt Blood presure

Risk of embolismRisk of myocardial infarct

The neurological complications of CEA

Intra- and postoperative factors determining CEA morbidity and mortality,the ways to prevent those, and drawbacks of preventative methods

Shunt Blood presure

Risk of embolismRisk of myocardial infarct

Myocardiac infarction ↓ Blood presure Risk of brain hypoperfusion

PostoperativeCarotid restenosis Angioplasty Duration of surgery

Brain hemorrhage Avoid ischemiaTreat HTA

IOM during carotid endarterectomy

During CEA surgery, a cross clamp mustbe applied to the proximal and distal endsof the surgery to be incrised and repaired20% carotid clamping results in a significant

cerebral ischemia with an associated highprobability of ischemic stroke

During CEA surgery, a cross clamp mustbe applied to the proximal and distal endsof the surgery to be incrised and repaired20% carotid clamping results in a significant

cerebral ischemia with an associated highprobability of ischemic stroke


Inherent risks associated with shunting may beattributed to the following factors:Intraoperative thrombosis formationTechnical problems that limit the surgeon’s ability to

expose and dissect the atheroma,especially the distalsegmentShunt kinking or occlusion due to improper

placement,resulting in ischemiaIncreased risk of cerebral embolization of

atherosclerotic debris and air into the distal cerebralcirculationPotential intimal damage resulting in postoperative

thrombosis at the operative

Inherent risks associated with shunting may beattributed to the following factors:Intraoperative thrombosis formationTechnical problems that limit the surgeon’s ability to

expose and dissect the atheroma,especially the distalsegmentShunt kinking or occlusion due to improper

placement,resulting in ischemiaIncreased risk of cerebral embolization of

atherosclerotic debris and air into the distal cerebralcirculationPotential intimal damage resulting in postoperative

thrombosis at the operative


the potential usefulness of IOM in CEA isthreefold: (1) immediately after induction and before any surgical

maneuver to check whether head positioning is welltolerated (2) to decide whether a shunt should be installed and, in

the affirmative, whether the shunt is well functioning (3) to decide whether BP is compatible with sufficient

brain perfusion.In addition, IOM might provide useful information in orderto decide for combined carotid and coronary bypassgrafting (CABG) surgery.

the potential usefulness of IOM in CEA isthreefold: (1) immediately after induction and before any surgical

maneuver to check whether head positioning is welltolerated (2) to decide whether a shunt should be installed and, in

the affirmative, whether the shunt is well functioning (3) to decide whether BP is compatible with sufficient

brain perfusion.In addition, IOM might provide useful information in orderto decide for combined carotid and coronary bypassgrafting (CABG) surgery.

EEG Technique in CEA all authors have used symmetrical

montages. Channels that provide a frontoparietal &

frontotemperal coverage correlative with thedistribution of the blood supply of the superior andinferior M2 branch of the middle cerebral artery,respectively 4/8 channel IOM machine: F3-C3,F7-T3/T3-T5 and F4-T4,F8-

T4/T4-T6 or C3-P3,F7-T3/T3-T5 and C4-P4,F8-T4/T4-T6 16 channel IOM machine: F3-C3,C3-P3,F7-T3/T3-T5 and F4-

T4,C4-P4,F8-T4/T4-T6 UCLA(Nuwer,2008): F3-C’3, C’3-T3,T3-O1 and F4-C’4, C’4-

T4, T4-O2

all authors have used symmetricalmontages. Channels that provide a frontoparietal &

frontotemperal coverage correlative with thedistribution of the blood supply of the superior andinferior M2 branch of the middle cerebral artery,respectively 4/8 channel IOM machine: F3-C3,F7-T3/T3-T5 and F4-T4,F8-

T4/T4-T6 or C3-P3,F7-T3/T3-T5 and C4-P4,F8-T4/T4-T6 16 channel IOM machine: F3-C3,C3-P3,F7-T3/T3-T5 and F4-

T4,C4-P4,F8-T4/T4-T6 UCLA(Nuwer,2008): F3-C’3, C’3-T3,T3-O1 and F4-C’4, C’4-

T4, T4-O2

EEG Technique in CEA(cont.)

UCLA(Nuwer,2008):F3-C3, C3-T3,T3-O1and F4-C4, C4-T4,T4-O2

UCLA(Nuwer,2008):F3-C3, C3-T3,T3-O1and F4-C4, C4-T4,T4-O2


Filter: 0.3 and 70Hz (UCLA: 1 and 30Hz),notch filter ONSensivity:3-5µV/mmCompressing the EEG with a slow time

base: 5-15mm/s( normal: 30mm/s)

Filter: 0.3 and 70Hz (UCLA: 1 and 30Hz),notch filter ONSensivity:3-5µV/mmCompressing the EEG with a slow time

base: 5-15mm/s( normal: 30mm/s)


At least 10minutes of preclamp baseline EEGbe record while the patient is anasthesized toappreciate any clamp associated changesAdjusting gain until the fast activity pattern

produces a deflection of about 1cm help detectthe signs of ischemiaAn asymmetric EEG usually occurs with

antecedent cerebral lesionClamp related EEG changes usually occur

within 1 minute

At least 10minutes of preclamp baseline EEGbe record while the patient is anasthesized toappreciate any clamp associated changesAdjusting gain until the fast activity pattern

produces a deflection of about 1cm help detectthe signs of ischemiaAn asymmetric EEG usually occurs with

antecedent cerebral lesionClamp related EEG changes usually occur

within 1 minute


The effect of clamping of the right internal carotid artery (ICA). Eight EEG channelsare shown and transcranial Doppler envelope for the ipsilateral middle cerebralartery

SEP Technique in CEA

SEP: almost use both Median and Tibial SEP,but could use alone upper/lower limb SEP(Median SEP more than Tibial SEP)SEP recordings should be obtained

preoperatively if possibleCertainly operative baselines should be obtains

prior to Carotid cross clamping(CCC).

SEP: almost use both Median and Tibial SEP,but could use alone upper/lower limb SEP(Median SEP more than Tibial SEP)SEP recordings should be obtained

preoperatively if possibleCertainly operative baselines should be obtains

prior to Carotid cross clamping(CCC).

SEP Technique in CEA(cont.)

Display cortical, subcortical and peripheralwaveforms if IOM machine enough channels.This allows more precise localization of ischemiaand helps with troublshooting.An attemp should be made to reproduce the SEP

waveforms every 30seconds during CCC toprovide rapid feedback.

Display cortical, subcortical and peripheralwaveforms if IOM machine enough channels.This allows more precise localization of ischemiaand helps with troublshooting.An attemp should be made to reproduce the SEP

waveforms every 30seconds during CCC toprovide rapid feedback.

EEG vesus SEP Technique in CEA

EEGmonitors the

spontaneous electricalactivity of corticalneurons and is widelyused to monitorcerebral perfusionduring CEA andendovascular procedure

SEP improve the ability to

detect deep brain andbrainstem ischemia.Ischemic damage tocortical or subcorticalneurons produces acharacteristic, detecablepattern: a decrease insignal amplitude &concomitant increase insignal latency.

monitors thespontaneous electricalactivity of corticalneurons and is widelyused to monitorcerebral perfusionduring CEA andendovascular procedure

improve the ability todetect deep brain andbrainstem ischemia.Ischemic damage tocortical or subcorticalneurons produces acharacteristic, detecablepattern: a decrease insignal amplitude &concomitant increase insignal latency.


EEG is limited by an inability

to detect subcorticalinjury, a high falsepositive rate (lowerspecility, mainly due tosentivitive to anesthesiaand drugs), and adiminished sentivity inpatients who have ahistory of stroke

SEPare particularly

useful for patienswho have an normalEEG as a result ofprior stroke

is limited by an inabilityto detect subcorticalinjury, a high falsepositive rate (lowerspecility, mainly due tosentivitive to anesthesiaand drugs), and adiminished sentivity inpatients who have ahistory of stroke

are particularlyuseful for patienswho have an normalEEG as a result ofprior stroke


EEGNormal mean cerebral blood

flow(CBF): 50ml/100g/minMild hypotension: 22-

50ml/100g/min,doesn’t induceneuronal perfusion.

Mean CBF< 22ml/100g/min:EEG amplitude decrease, and/orEEG slowing become manifest

Mean CBF 7-15ml/100g/min:suppresion of EEG activity

Mean CBF 12-15ml/100g/min:neural damage begin to occur,making EEG a useful monitor forcortical ischemia

SEPMean CBF 16-20ml/100g/min: cortical

waveform s amplitude decrease<50%Mean CBF <14ml/100g/min: cortical

waveforms amplitude decrease >50%,5% latency prolongatiionMean CBF 12-15ml/100g/min: Cortical

waveform s dissappear, subcorticalwaveform s amplitude decrease

But CBF values resulting in a loss ofspontaneous neuronal activities isextremely variable(6-22ml/100g/min).This large variability can be explainedby the differences among individualneurons in energy metabolism andlocal feature of blood supply

Normal mean cerebral bloodflow(CBF): 50ml/100g/min

Mild hypotension: 22-50ml/100g/min,doesn’t induceneuronal perfusion.

Mean CBF< 22ml/100g/min:EEG amplitude decrease, and/orEEG slowing become manifest

Mean CBF 7-15ml/100g/min:suppresion of EEG activity

Mean CBF 12-15ml/100g/min:neural damage begin to occur,making EEG a useful monitor forcortical ischemia

Mean CBF 16-20ml/100g/min: corticalwaveform s amplitude decrease<50%Mean CBF <14ml/100g/min: cortical

waveforms amplitude decrease >50%,5% latency prolongatiionMean CBF 12-15ml/100g/min: Cortical

waveform s dissappear, subcorticalwaveform s amplitude decrease

But CBF values resulting in a loss ofspontaneous neuronal activities isextremely variable(6-22ml/100g/min).This large variability can be explainedby the differences among individualneurons in energy metabolism andlocal feature of blood supply

EEG & SEP criteria for alam in CEA

Diagnosis EEG SEPsMild <50% decrease of fast activities (+)

<50% increase of slow activities (+)Desynchronization ordisappearance of the frontalN30 and/or parietal P45

Moderate >50% decrease of fast activities (+)>50% increase of slow activities (+)

Desynchronization ordisappearance of the parietalP27 (early warning) or P27 andP24 (urgent warning)

>50% decrease of fast activities (+)>50% increase of slow activities (+)

Desynchronization ordisappearance of the parietalP27 (early warning) or P27 andP24 (urgent warning)

Severe EEG loss over all frequency bandsBurst suppression

Disappearance of all activitiesfollowing N20Desynchronization ordisappearance of N20

Criteria of mild, moderate, and severe EEG and SEP changes suggestive ofimpaired brain perfusion (Guérit et al.,1997; Smith and Prior, 2003)

Evidence supporting use of IOM inCEA

It is difficult whether IOM with EEG or SEP helpsdecrease the morbidity of CEA, as most surgeon shuntthe carotid artery if neurophysiological changes arenoted

Florent et al(2004)

This analysis suggests that there is no clear superiorityof one technique over the other. Multimodallitymonitoring may be more effetive than any singlemodality alone.

Sensivity Specificity

It is difficult whether IOM with EEG or SEP helpsdecrease the morbidity of CEA, as most surgeon shuntthe carotid artery if neurophysiological changes arenoted

Florent et al(2004)

This analysis suggests that there is no clear superiorityof one technique over the other. Multimodallitymonitoring may be more effetive than any singlemodality alone.

Sensivity SpecificityEEG 0.27 0.87SEP 0.52 0.98

Proposed decision algorithms before the cross-clampingperiod.

Proposed decision algorithms during the cross-clampingperiod.


IOM modalities:EEGSEP

Transcranial doppler(TCD): intraoperativedetection of microembolism

Proved extremely sensitive to hemodynamic disturbances andmacroembolism

IOM modalities:EEGSEP

Transcranial doppler(TCD): intraoperativedetection of microembolism


IOM modalities:EEG:EEG+SEPUCLA:The vascular surgeons like EEG for CEA.The neurosurgeons like both EEG and SEP. EEG covers a wider area and is more sensitive to changes. SEP is covers a more restricted region, and only changes when

the ischemia is more severe. It is a choice as to what to do

IOM modalities:EEG:EEG+SEPUCLA:The vascular surgeons like EEG for CEA.The neurosurgeons like both EEG and SEP. EEG covers a wider area and is more sensitive to changes. SEP is covers a more restricted region, and only changes when

the ischemia is more severe. It is a choice as to what to do

Technical considerations

There are many patients-relatedconditions that may effect IOM.Prior stroke , demyelinating disease may result in

slowing of EEG frequencies at baseline→keep inmind in interpreting focal slowing after CCCThe presence of peripheral neuropathy,

neuromuscular disorder,myelopathy, cerebralpalsy: may effect SEPs

There are many patients-relatedconditions that may effect IOM.Prior stroke , demyelinating disease may result in

slowing of EEG frequencies at baseline→keep inmind in interpreting focal slowing after CCCThe presence of peripheral neuropathy,

neuromuscular disorder,myelopathy, cerebralpalsy: may effect SEPs

Technical considerations

Procedure8 channel IOM machine:At least 4 EEG channels are usedSEP: C3,Cz,C4,CSp5

16 channel IOM machineAnterio-posterior longitudinal montage shoul be usedMedian and tibial SEPs

Communication between IOM,surgery andanesthesia teams is critical for optimalmonitoring

Procedure8 channel IOM machine:At least 4 EEG channels are usedSEP: C3,Cz,C4,CSp5

16 channel IOM machineAnterio-posterior longitudinal montage shoul be usedMedian and tibial SEPs

Communication between IOM,surgery andanesthesia teams is critical for optimalmonitoring

Conclusion

IOMduring CEA can provide the surgeonwith critical information that may modifysurgical procedure.A complementary working environment

between IOM,suregy,anesthesia team willensure the best monitoring

IOMduring CEA can provide the surgeonwith critical information that may modifysurgical procedure.A complementary working environment

between IOM,suregy,anesthesia team willensure the best monitoring

Thank you for your attention

iom during carotid endarterectomy 2008

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