European Journal of Vascular & Endovascular Surgery
Volume 38, Issue 5 , Pages 539-545, November 2009

The Value of Near-Infrared Spectroscopy Measured Cerebral Oximetry During Carotid Endarterectomy in Perioperative Stroke Prevention. A Review

  • C.W.A. Pennekamp

      Affiliations

    • Department of Vascular Surgery (G04.129), University Medical Center Utrecht, Postbus 85500, 3508 GA Utrecht, The Netherlands
    • ,
  • M.L. Bots

      Affiliations

    • Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Postbus 85500, 3508 GA Utrecht, The Netherlands
    • ,
  • L.J. Kappelle

      Affiliations

    • Department of Neurology, University Medical Center Utrecht, Postbus 85500, 3508 GA Utrecht, The Netherlands
    • ,
  • F.L. Moll

      Affiliations

    • Department of Vascular Surgery (G04.129), University Medical Center Utrecht, Postbus 85500, 3508 GA Utrecht, The Netherlands
    • ,
  • G.J. de Borst

      Affiliations

    • Department of Vascular Surgery (G04.129), University Medical Center Utrecht, Postbus 85500, 3508 GA Utrecht, The Netherlands
    • Corresponding Author InformationCorresponding author. Tel.: +31 88 7556965.

Received 17 March 2009; accepted 13 July 2009. published online 10 August 2009.

Article Outline

Abstract 

Background

Transcranial Doppler (TCD) for identification of patients at risk for cerebral hyperperfusion syndrome (CHS) following carotid endarterectomy (CEA) cannot be performed in 10–15% of patients because of the absence of a temporal bone window. Near-infrared spectroscopy (NIRS) may be of additional value in these patients. We aimed to (1) compare the value of NIRS related to existing cerebral monitoring techniques in prediction of perioperative cerebral ischaemia and (2) compare the relation between NIRS and the occurrence of CHS.

Methods

A systematic literature search relating to NIRS and CEA was conducted in PubMed and EMBASE databases. Those included were: (1) prospective studies; (2) on NIRS for brain monitoring during CEA; (3) including comparison of NIRS to any other intra-operative cerebral monitoring systems; and (4) on either symptomatic or asymptomatic patients.

Results

We identified 16 studies, of which 14 focussed on the prediction of intra-operative cerebral ischaemia and shunt indication. Only two studies discussed the ability of NIRS in predicting CHS. NIRS values correlated well with TCD and electroencephalography (EEG) values indicating ischaemia. However, a threshold for postoperative cerebral ischaemia could not be determined. Neither could a threshold for selective shunting be determined since shunting criteria varied considerably across studies. The evidence suggesting that NIRS is useful in predicting CHS is modest.

Conclusion

NIRS seems a promising monitoring technique in patients undergoing CEA. Yet the evidence to define clear cut-off points for the presence of perioperative cerebral ischaemia or identification of patients at high risk of CHS is limited. A large prospective cohort study addressing these issues is urgently needed.

Keywords: Near-infrared spectroscopy (NIRS), Cerebral oximetry, Perioperative stroke prevention, Carotid endarterectomy (CEA), Cerebral hyperperfusion syndrome (CHS), Transcranial Doppler (TCD)

 

The benefit of carotid endarterectomy (CEA) is hampered by a 2–5% perioperative stroke rate.1 Many aetiologies of stroke following CEA have been proposed; of which the most significant are ischaemia from prolonged carotid artery clamping, intra-operative or postoperative thrombosis and embolism and postoperative cerebral hyperperfusion syndrome (CHS).2 With the introduction of intra-operative cerebral monitoring during CEA, the intra-operative stroke rate declined, but the rate of postoperative stroke was not altered.3 Postoperative CHS still occurs in 1–3% of CEA patients, and the knowledge of causes and prevention among physicians seems limited.4 CHS that causes intracerebral haemorrhage is associated with a 40% mortality rate.

Currently, electroencephalography (EEG) and transcranial Doppler (TCD) are the most frequently used methods for intra-operative monitoring in the prevention of cerebral ischaemia.5 EEG measures electrical activity produced by the brain recorded by electrodes placed on the scalp. TCD detects changes in cerebral blood flow (CBF) by measuring the flow velocity in the middle cerebral artery (FVmca) during and following CEA.3, 6 An increase of ≥100% of postoperative CBF, as compared to preoperative CBF values, has been associated with a 10 times higher risk for CHS. TCD however cannot be performed in all patients, since a temporal bone window is missing in 10–15% of CEA patients. Especially for this subgroup, a reliable alternative monitoring technique is required, but not yet available. Near-infrared spectroscopy (NIRS) has been suggested as an alternative cerebral monitoring technique. NIRS is a non-invasive technique that allows continuous monitoring of cerebral haemoglobin oxygen desaturation produced by systemic hypoxaemia.5 Yet, the information on NIRS appears to be modest.7, 8, 9 Therefore, in the present study, we performed a systematic literature review to (1) compare the value of NIRS related to existing cerebral monitoring techniques in prediction of intra- and postoperative cerebral ischaemia and (2) compare the relation between intra-operative NIRS values and risk of occurrence of postoperative CHS in patients undergoing CEA.

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Methods 

Search strategy 

A literature search on all studies related to NIRS and CEA was conducted in December 2008. Studies were initially identified from PubMed and EMBASE databases using synonyms for the following search terms:

#1(Carotid endarterectomy) OR (CEA) OR (carotid revascularization) OR (carotid deobstruction)

#2(NIRS) OR (near-infrared spectroscopy) OR (infrared spectroscopy)

#3(Hyperperfusion syndrome) OR (cerebral hyperperfusion)

Two researchers (CP and GB) independently screened the articles consecutively on title, abstract and full text. Additional studies were identified by searching the reference list of relevant studies identified. Titles and abstracts were retrieved by two independent reviewers separately (CWAP, GJdB). Doubts and differences of opinion were resolved by an open discussion.

The inclusion criteria were (1) prospective studies; (2) on NIRS for brain monitoring during CEA; (3) including comparison of NIRS to any other intra-operative cerebral monitoring systems; and (4) on either symptomatic or asymptomatic patients. Reasons for exclusion were (1) type of study design (retrospective, case report), (2) language difficulties (non-English papers), (3) full-text papers that were unavailable; (4) standardised intra-operative shunt insertion, or (5) a comparison with a non-regulatory monitoring method.

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Results 

Result of search strategy 

To address our first objective, our search generated 166 and 193 hits in PubMed and EMBASE, respectively. Of these, following exclusion of double hits, 184 studies were screened on title and abstract and 33 studies were further assessed. Finally, 14 studies met the inclusion criteria and were included for further analysis (Fig. 1; search 1).

To address our second objective, we reviewed the relationship between intra-operative NIRS monitoring and the occurrence of CHS, and our search yielded two and four hits in PubMed and EMBASE, respectively. Only two studies fulfilled our search criteria and were included (Fig. 1; search 2).

Data analytic approach 

No effort was made to pool findings from the different studies into one estimate, because the studies varied too much in presentation, cut-off points used, study population and other characteristics. Therefore, results of the analysis of selected studies are presented in a descriptive manner.

Technical aspects of NIRS application 

In nine of the 12 (search 1) studies, the Invos 3100 or the Invos 4100 (Somanetics Corp., Troy, MI, USA) or the OM220 (Shimadzu Co., Japan) were used. The remaining three studies used the NIRO 300 (Hamamatsu Photonics),10 NIR 500 and NIR 1000 (Hamamatsu, London, UK), respectively, by penetrating the scalp and brain tissue whereby the skin, scull and other tissues are relatively transparent to near-infrared wavelengths of light. By using two detectors, the light reflected and transmitted by the superficial extracranial tissues is subtracted, resulting in a signal derived from brain tissue, the so-called regional haemoglobin oxygen saturation (rSO2) index.11 The changes in concentrations of oxygenated and deoxygenated haemoglobin are measured by a modified Beer–Lambert method. Because of the different wavelengths of the oxygenated and deoxygenated haemoglobin, these can be distinguished and the ratio of oxygenated haemoglobin to total tissue haemoglobin (TOI) can be defined.12 The cerebral oximetry sensors were placed on the forehead, ipsilateral to the surgical site in seven studies, bilateral in five studies and an unspecified location in two studies.

NIRS compared with TCD sonography 

In five of the 14 studies, NIRS was compared with TCD.6, 10, 12, 13, 14 The results are described in Table 1. These studies comprised 352 patients with either symptomatic or asymptomatic but haemodynamically significant stenosis. In three studies, cerebral function monitoring (CFM) was additionally used for detection of signs of cerebral ischaemia.10, 13, 14, 15 An adequate TCD signal could not be obtained in 10%.6, 12, 14

Table 1. NIRS compared with transcranial Doppler (TCD) to detect intraoperative ischemia.
StudyMethodsIndicationRel. FV/ΔrSO2rSO2 SCISens. (%)Spec. (%)PPV (%)NPV (%)
Al Rawi and Kirkpatrick10N=167
TCD

CFM

<40% or CFMr=0.74, P<.01Δ13%1009376100
Vets et al.6N=14
TCD

EEG

<20%r=0.72, P=.02Δ13%1007833100
Grubhofer et al.12N=55TCD<20%r=0.63, P<.01
Δ13%

Δ12%

Δ11%


100

100

100


87

83

83


22

18

25


100

100

100

Kirkpatrick et al13N=76
TCD

CFM

<40% and CFMr=0.73, P<.01>6.8a8110010095
Kirkpatrick et al14N=13CFM<50% and CFMr=0.61NANANANANA

NIRS, Near-infrared spectroscopy; Methods, Used measuring methods: transcranial Doppler (TCD), cerebral function monitoring (CFM), electroencephalography (EEG); Indication, Indication for shunting. Threshold for performing a shunt measured in decrease of bloodflow measured by TCD (of preclamp value) and/or a persistent respectively a sustained fall in CBF of longer than one minute measured by CFM; Rel. FV/ΔrSO2, Relationship between flow volume in the middle cerebral artery and changes in regional cerebral oxygenation (rSO2); rSO2 SCI, rSO2 Value measured by NIRS when severe critical ischemia (SCI) occurs identified by transcranial Doppler; Sens., Sensitivity (%); Spec., Specificity (%); PPV, Positive predictive value (%); NPV, Negative predictive value (%); NA, Not available.

aICA Hbdiff (μmol): total difference in concentrations of oxyhemoglobin and deoxyhemoglobi by clamping the internal carotid artery (ICA).

In 16.8% of the population, a shunt was placed on which thresholds for severe critical ischaemia measured by NIRS were determined in four studies. The indication for shunt insertion, however, varied considerably across studies: from a decrease in mean velocity less than 50% to less than 20% of the preclamp value. Some authors used a shunt only if CFM indicated cerebral ischaemia, defined as a persistent sustained fall in CBF of longer than 1min.10, 14 In another study, a shunt was used only if it was based on signs of severe cerebral ischaemia measured both by TCD in combination with a sustained fall in CFM (>1min).13

Four out of five studies reported a significant positive relationship between changes in FVmca and rSO2 on clamping.6, 10, 12, 13 The magnitude of the relationship between NIRS-measured rSO2 and TCD-measured FVmca using linear regression ranged from 0.43 to 0.74. No conclusive data on the value of NIRS in the decision for shunt insertion could be obtained.

NIRS compared with electroencephalography (EEG) 

In four of 15 studies, both EEG and NIRS were used for brain monitoring during CEA.7, 15, 16, 17 In three of these, EEG was compared with NIRS in detection of intra-operative severe cerebral ischaemia.7, 16, 17 Yamamoto et al. only shunted their last 15 patients selectively and this report was left out of analysis.15 The other three studies comprised 228 patients with symptomatic or asymptomatic carotid stenosis. The threshold for critical ischaemia used was the asymmetry of the ipsi- and contralateral EEG, further defined with a cut-off value of >0.7Hz17 and asymmetry >20%.16 A significant correlation between EEG and rSO2 was found in all three studies. Shunt percentages varied from 6% to 17%. Thresholds for reduction in rSO2 associated with severe critical ischaemia varied from 5% to 25%.

NIRS compared with stump pressure (SP) 

NIRS has been compared with stump pressure (SP) during CEA in two studies (Table 2) comprising 105 patients.15, 17 In one study, EEG was used as a third monitoring entity.15 In both studies, a shunt was used when SP decreased below 40mmHg. A shunt was placed in 13% of the patients reported by Kragsterman, whereas shunt use in the study by Yamamoto was irrelevant for our analysis, since only their last 15 patients were shunted selectively. A significant correlation was shown between the change of the regional saturation of the frontal lobe (SdO2) and the stump pressure after cross-clamping the common carotid artery (CCA)15 or the internal carotid artery (ICA).17 In the study by Yamamoto, a SP of 40mmHg was equivalent to an SdO2 decrease of 4.1%, whereas in the Kragsterman study no threshold could be defined.

Table 2. NIRS compared with electroencephalography (EEG) to detect intraoperative ischemia.
EEGIndicationrSO2 SCISens. (%)Spec. (%)PPV (%)NPV (%)
Rigamonti et al.7N=49Asymmetry NS
Δ15%

P<.01

4482NA94
Hirofumi et al.17N=20Asymmetry >0.7HzΔ25%100100100100
De Letter et al16N=101Asymmetry >20%Δ5%1004427100

NIRS, Near-infrared spectroscopy; Indication, Indication for shunting: Threshold for performing a shunt measured by EEG; Asymmetry, asymmetry of the ipsi- and contralateral EEG; NS, Not specified; rSO2 SCI, rSO2 Value measured by NIRS if severe critical ischemia (SCI) occurred, identified by EEG; Sens., Sensitivity (%); Spec., Specificity (%); PPV, Positive predictive value (%); NPV, Negative predictive value (%); NA, Not available and could not be calculated from the available data.

NIRS compared with somatosensory evoked potentials (SSEPs) 

NIRS has been compared with SSEP as a monitoring method for cerebral ischaemia in two studies.18, 19 However, since the reliability of SSEP is under discussion and its use in CEA nowadays is scarce, and since there is no consensus about the cut-off point in detecting cerebral ischaemia, we felt that a comparison with NIRS was not appropriate.

NIRS compared with clinical signs of ischaemia 

Regional anaesthesia allows the use of clinical signs of cerebral ischaemia as a monitoring method. In two studies, clinical signs and NIRS were used.5, 7 Moritz and co-workers studied 48 patients.5 A shunt was used following the occurrence of any new neurological deficit such as speech abnormalities, motor weakness or impaired consciousness. In 17% of patients, an intravascular shunt was placed. An absolute rSO2 cut-off value below 59% in NIRS was defined as a threshold for severe cerebral ischaemia indicative for shunt placing, with a positive predictive value of 39%.

NIRS and prediction of cerebral hyperperfusion syndrome (CHS) 

In two studies (139 patients) NIRS was related to the risk of CHS.8, 9 No intraluminal shunts were used in this patient group. Neurological expression of CHS was clinically diagnosed by either decreased consciousness level, occurrence of seizures and development of focal neurological signs, such as motor weakness, or a combination of these symptoms. Using monitoring techniques, CHS was suspected in case of evidence of hyperperfusion on single photon emission computed tomography (SPECT), or doubling of cerebral blood flow (CBF) on TCD performed during CEA. Post-CEA hyperperfusion was reported in 11%8 and 12%9 of patients, whereas 1.4% of the patients developed CHS (Table 3). In all patients with CHS the rSO2 values exceeded 105% of the post-clamping value and exceeded the 110% of preclamping values by the end of the procedure (Table 4). A reduced cerebrovascular reactivity (CVR) and reduced SO2 ratio (SO2 5min before clamping/SO2 lowest value during clamping) were significant independent predictors of the development of hyperperfusion after CEA.

Table 3. Post-CEA hyperperfusion based on SPECT-imaging post-CEA.
Mean age (yrs)Ischemia post-CEAPost-CEA hyperperfusionCHS 6th day postop. (%)
Komoribayashi et al.8N=8968210 (11%)2 (2.2%)
Ogasawara et al.9N=506906 (12%)1 (2%)

CEA, Carotid endarterectomy; Ischemia post-CEA., New postoperative neurological deficit; Post-CEA hyperperfusion, Hyperperfusion, defined as an increase of cerebral blood flow of >100%, compared with preoperative values after carotid endarterectomy; CHS 6th day postop., Cerebral hyperperfusion syndrome on the 6th day after operation.

Table 4. Relationship between the cerebral blood flow (CBF) and the rSO2 ratio after cross-clamping for patients with hyperperfusion.
Ogasawara et al.9N=50%rSO2 increase of preclamping valueSens. (%)Spec. (%)PPV (%)NPV (%)
rSO2 post-CEA
>5%

r2=0.247, P<.01

10086.450100
rSO2 at the end of the procedure
>10%

r2=0.822, P<.01

100100100100

%rSO2 Increase of preclamping value, Relative increase of regional cerebral oxygen saturation compared with the preclamping value; Sens., Sensitivity (%); Spec., Specificity (%); PPV, Positive predictive value (%); NPV, Negative predictive value (%).

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Discussion 

TCD and EEG are currently the gold standard in brain monitoring during CEA.3, 20 However, both modalities have certain disadvantages. TCD monitoring cannot be performed in around 10% of the patients, because of missing a temporal bone window. Moreover, TCD is expensive and dependent on the skills of the technicians. EEG monitoring is time consuming, sometimes difficult to interpret and influenced by certain anaesthetics.

As an alternative cerebral monitoring entity, NIRS offers a non-invasive technique, which is easy and quick to apply.21 Especially for the subgroup in which TCD cannot be applied, NIRS might be helpful in identifying a threshold for postoperative risk for CHS. NIRS however has its own disadvantages: only the local conditions of the frontal lobe, supplied by the anterior cerebral artery, are measured and perfusion changes in other brain areas might escape detection.

In the present review, only 14 studies discussing the potential of NIRS in predicting intra-operative cerebral ischaemia could be identified. In several studies performed for intra-operative monitoring during CEA, NIRS values were significantly related to the results of TCD and EEG. Nevertheless, the reviewed studies had certain drawbacks, thereby limiting the quality of analysis of the reviewed data. In most reports, the investigated study cohort was small and the reference test chosen did not reflect the gold standard. Furthermore, different cut-off values were used. The most reliable cut-off value to determine severe critical ischaemia was obtained in an awake patient, using regional anaesthesia. A TCD-measured reduction of 70%3 of CBF provided a PPV of 71%, whereas EEG provided a PPV of 86.4%.22, 23 A threshold for obtained NIRS values below which shunting should be indicated could not be determined in a valid manner, since criteria used for shunting varied considerably across studies. Similarly, a NIRS value, based upon which cerebral ischaemia was likely to occur postoperatively, could not be determined from the literature due to large variability in patients and approaches taken. The evidence suggesting that NIRS is useful in predicting CHS is modest. However, the two reports focussing on NIRS application and the occurrence of CHS are consistent in their findings: in all patients with diagnosed CHS the rSO2 values exceeded 105% of the post-clamping value and exceeded 110% of preclamping values by the end of the procedure. In other words, the positive predictive value of NIRS in predicting CHS based on only two prospective studies seems high. NIRS therefore might offer a promising technique in the detection of post-CEA patients at risk for CHS development, which should be reaffirmed in further future clinical trials.

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Conclusion 

NIRS seems a promising perioperative cerebral monitoring technique in CEA. Yet the evidence to define clear cut-off points for either presence of intra- or postoperative cerebral ischaemia or for identification of patients at high risk of a CHS is limited. A large cohort study addressing these issues in a prospective and systematic manner is urgently needed, before NIRS can be possibly used as a standard monitoring technique for the prevention of peri- and postoperative stroke from CEA.

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Conflict of Interest/Funding 

None

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References 

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PII: S1078-5884(09)00383-9

doi:10.1016/j.ejvs.2009.07.008

European Journal of Vascular & Endovascular Surgery
Volume 38, Issue 5 , Pages 539-545, November 2009

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