Comparison of cerebral oximeter and evoked potential monitoring in carotid endarterectomy

Monitoring in carotid endarterectomy

Cerebral ischemia during carotid endarterectomy occurs via several mechanisms: inadequate collateral blood flow during carotid cross-clamping, thromboembolism due to carotid manipulation, and/or rethrombosis at the surgical site. Perioperative strokes increase not only the morbidity of endarterectomy but also its short- and long-term mortality. However, while several predictors of cerebral ischemia have been identified, precise individual risk is hard to assess. Since nonselective shunting during carotid cross-clamping is neither risk-free nor eliminates perioperative stroke, it is advisable to apply intraoperative monitoring techniques for detection and reversal of cerebral ischemia, which may occur at various stages of the procedure. This chapter addresses the methods available for monitoring, with an emphasis on neurophysiologic techniques, which are preferable given their direct assessment of how a decrease in cerebral blood flow impacts brain function. These include electroencephalography, somatosensory evoked potentials, and transcranial motor evoked potentials. Details regarding the methodology, advantages, disadvantages, and interpretation of these tests will be discussed within the anatomic, physiologic, surgical, and anesthetic contexts.

Overview and Diagnostic Accuracy of Near Infrared Spectroscopy in Carotid Endarterectomy: A Systematic Review and Meta-analysis

OBJECTIVE

Carotid endarterectomy is recommended for the prevention of ischaemic stroke due to carotid stenosis. However, the risk of stroke after carotid endarterectomy has been estimated at 2% - 5%. Monitoring intra-operative cerebral oxygenation with near infrared spectroscopy (NIRS) has been assessed as a strategy to reduce intra- and post-operative complications. The aim was to summarise the diagnostic accuracy of NIRS to detect intra-operative ischaemic events, the values associated with ischaemic events, and the relative contribution of external carotid contamination to the NIRS signal in adults undergoing carotid endarterectomy.

DATA SOURCES

EMBASE, MEDLINE, Cochrane Centre Register of Controlled Trials, and reference lists through May 2019 were searched.

REVIEW METHODS

Non-randomised and randomised studies assessing NIRS as an intra-operative monitoring tool in carotid endarterectomy were included. Studies using NIRS as the reference were excluded. Risk of bias was assessed using the Newcastle Ottawa Scale, RoB-2, and QUADAS-2.

RESULTS

Seventy-six studies were included (n = 8 480), under local (n = 1 864) or general (n = 6 582) anaesthesia. Seven studies were eligible for meta-analysis (n = 524). As a tool for identifying intra-operative ischaemia, specificity increased with more stringent NIRS thresholds, while there was unpredictable variation in sensitivity across studies. A Δ20% threshold under local anaesthesia resulted in pooled estimates for sensitivity and specificity of 70.5% (95% confidence interval, CI, 54.1 - 82.9) and 92.4% (95% CI 85.5 - 96.1) compared with awake neurological monitoring. These studies had low or unclear risk of bias. NIRS signal consistently dropped across clamping and recovered to pre-clamp values upon de-clamp in most studies, and larger decreases were observed in patients with ischaemic events. The contribution of extracranial signal to change in signal across clamp varied from 3% to 50%.

CONCLUSION

NIRS has low sensitivity and high specificity to identify intra-operative ischaemia compared with awake monitoring. Extracranial signal contribution was highly variable. Ultimately, data from high quality studies are desperately needed to determine the utility of NIRS.

Loss of Motor Evoked Potentials Due to Carotid Artery Retraction in an Exoscopic Clipping of a Basilar Tip Aneurysm

The internal carotid artery (ICA) may inhibit visualization of a basilar tip aneurysm during an orbitozygomatic craniotomy. Retraction of the ICA may be warranted for better visualization; however, it may lead to impending neurological sequelae. Impending neurological injury due to ICA retraction may be mitigated if multi-modal neuromonitoring techniques are employed. The authors present a case report showing the contemporaneous loss of transcranial motor evoked potentials and direct cortical motor evoked potentials during an exoscopic clipping of a basilar tip aneurysm due to ICA retraction and subsequent loss of perfusion to the vascular territory supplied by ICA. The motor evoked potentials immediately returned after retraction was removed and the patient awoke neurologically intact.

Association of biomarker S100B and cerebral oximetry with neurological changes during carotid endarterectomy performed in awake patients

Background: This study attempted to correlate neurological symptoms in awake patients undergoing carotid endarterectomy (CEA) under local anaesthesia (LA) with serum concentration of S100B protein and measurement of cerebral oximetry with near-infrared spectroscopy (NIRS). Patients and methods: A total of 64 consecutive CEAs in 60 patients operated under LA during an 18-month period were prospectively evaluated. A cerebral oximeter was used to measure cerebral oxygen saturation (rSO₂) before and after cross-clamping along with serum concentration of the S100B protein. Selective shunting was performed when neurological changes occurred, regardless of NIRS. Neurological deterioration occurred (neurological symptoms group) in 7 (10.9 %) operations. In 57 (89.1 %) operations, the patients were neurologically stable (no neurological symptoms group). Results: The neurological symptoms that occurred after clamping correlated with an increase in the serum level of S100B (P = .040). The cut-off of 22.5 % of S100B increase was determined to be optimal for identifying patients with neurological symptoms. There was no correlation between rSO₂ decline and neurological symptoms (P = .675). Two (3.1 %) perioperative strokes occurred. Conclusions: We found a correlation between neurological symptoms and serum S100B protein increase. However, because of the long evaluation time of serum S100B, this monitoring technique cannot be performed during CEA.

Systematic review of near-infrared spectroscopy determined cerebral oxygenation during non-cardiac surgery

Near-infrared spectroscopy (NIRS) is used to monitor regional cerebral oxygenation (rScO₂) during cardiac surgery but is less established during non-cardiac surgery. This systematic review aimed (i) to determine the non-cardiac surgical procedures that provoke a reduction in rScO₂ and (ii) to evaluate whether an intraoperative reduction in rScO₂ influences postoperative outcome. The PubMed and Embase database were searched from inception until April 30, 2013 and inclusion criteria were intraoperative NIRS determined rScO₂ in adult patients undergoing non-cardiac surgery. The type of surgery and number of patients included were recorded. There was included 113 articles and evidence suggests that rScO₂ is reduced during thoracic surgery involving single lung ventilation, major abdominal surgery, hip surgery, and laparoscopic surgery with the patient placed in anti-Tredelenburg's position. Shoulder arthroscopy in the beach chair and carotid endarterectomy with clamped internal carotid artery (ICA) also cause pronounced cerebral desaturation. A >20% reduction in rScO₂ coincides with indices of regional and global cerebral ischemia during carotid endarterectomy. Following thoracic surgery, major orthopedic, and abdominal surgery the occurrence of postoperative cognitive dysfunction (POCD) might be related to intraoperative cerebral desaturation. In conclusion, certain non-cardiac surgical procedures is associated with an increased risk for the occurrence of rScO₂. Evidence for an association between cerebral desaturation and postoperative outcome parameters other than cognitive dysfunction needs to be established.

Application of a time-resolved optical brain imager for monitoring cerebral oxygenation during carotid surgery

Recent studies have shown that time-resolved optical measurements of the head can estimate changes in the absorption coefficient with depth discrimination. Thus, changes in tissue oxygenation, which are specific to intracranial tissues, can be assessed using this advanced technique, and this method allows us to avoid the influence of changes to extracerebral tissue oxygenation on the measured signals. We report the results of time-resolved optical imaging that was carried out during carotid endarterectomy. This surgery remains the "gold standard" treatment for carotid stenosis, and intraoperative brain oxygenation monitoring may improve the safety of this procedure. A time-resolved optical imager was utilized within the operating theater. This instrument allows for the simultaneous acquisition of 32 distributions of the time-of-flight of photons at two wavelengths on both hemispheres. Analysis of the statistical moments of the measured distributions of the time-of-flight of photons was applied for estimating changes in the absorption coefficient as a function of depth. Time courses of changes in oxy- and deoxyhemoglobin of the extra- and intracerebral compartments during cross-clamping of the carotid arteries were obtained. A decrease in the oxyhemoglobin concentration and an increase in the deoxyhemoglobin concentrations were observed in a large area of the head. Large changes were observed in the hemisphere ipsilateral to the site of clamped carotid arteries. Smaller amplitude changes were noted at the contralateral site. We also found that changes in the hemoglobin signals, as estimated from intracerebral tissue, are very sensitive to clamping of the internal carotid artery, whereas its sensitivity to clamping of the external carotid artery is limited. We concluded that intraoperative multichannel measurements allow for imaging of brain tissue hemodynamics. However, when monitoring the brain during carotid surgery, a single-channel measurement may be sufficient.

Cerebral oximetry and stump pressure as indicators for shunting during carotid endarterectomy: comparative evaluation

The purpose of this work is to investigate the correlation between regional oxygen saturation (rSO2) changes and stump pressure (SP) during cross-clamping of the internal carotid artery in carotid endarterectomy (CEA) and verify the perspectives of rSO2 to become a criterion for shunting. Sixty consecutive CEAs under general anesthesia were studied prospectively. Selective shunting was based on SP ≤40 mmHg exclusively. Regression analysis with high order terms and receiver operating characteristic analysis were performed to investigate the association between ΔrSO2(%) and SP and to determine an optimal ΔrSO2(%) threshold for shunt insertion. A quadratic association between ΔrSO2(%) and SP was documented regarding the baseline to one and five minutes after cross-clamping intervals. A cut-off of 21 and 10.1% reduction from the baseline recording was identified as optimal for the distinction between patients needed or not a shunt regarding the first and fifth minute after cross-clamping, respectively. In conclusion, cerebral oximety reflects sufficiently cerebral oxygenation during CEA compared with SP, providing a useful mean for cerebral monitoring.

SELECTIVE VERSUS ROUTINE INTRAOPERATIVE SHUNTING DURING CAROTID ENDARTERECTOMY

OBJECTIVE

The use of intraluminal shunting during carotid endarterectomy (CEA) remains controversial. Over the years, different shunting strategies have been used. More recently, the use of intraoperative electroencephalography and somatosensory evoked potential monitoring with selective intraluminal shunting has been explored. No studies have assessed the independent association of selective versus routine intraluminal shunting to outcomes after CEA.

METHODS

The clinical and radiological records of all patients undergoing CEA from 1994 to 2006 at an academic institution were reviewed retrospectively to assess outcomes at 72 hours. The independent association of selective intraluminal carotid artery shunting during CEA and perioperative stroke within 72 hours was assessed through multivariate logistic regression analysis.

RESULTS

In 1411 patients with both symptomatic and asymptomatic extracranial carotid artery disease, there were a total of 49 (3.5%) perioperative strokes after CEA. There were two (1%) cases of perioperative strokes among 194 patients in the selective shunting group compared with 47 out of 1217 (4%) in the routine shunting group (P = 0.04). Symptomatic carotid artery disease was associated with a twofold increase in the odds of experiencing perioperative stroke (odds ratio, 1.95; 95% confidence interval, 1.08–3.52; P = 0.03). Patients undergoing electrophysiological monitoring with selective intraluminal carotid artery shunting were more than seven times less likely to experience a perioperative stroke (odds ratio, 0.05; 95% confidence interval, 0.01–0.40; P < 0.01). Increasing cumulative surgical volume, particularly more than 200 total cases, was associated with more than a twofold decrease in perioperative stroke (odds ratio, 0.38; 95% confidence interval, 0.20–0.74; P < 0.01).

CONCLUSION

Regardless of symptomatic carotid artery disease or cumulative surgical volume, patients undergoing CEA with intraoperative electroencephalography and somatosensory evoked potential monitoring with selective intraluminal carotid artery shunting had a stroke rate lower than that of the routine shunting group. Selective shunting based on electroencephalography and somatosensory evoked potential monitoring may be superior to the nonselective strategy.

Tissue oxygen index: thresholds for cerebral ischemia using near-infrared spectroscopy

BACKGROUND AND PURPOSE

To date, the clinical application of near infrared spectroscopy in the adult brain has been limited. The NIRO 300 (Hamamatsu Photonics) provides a continuous measurement of tissue oxygen index (TOI) using spatially resolved spectroscopy. Although TOI reflects cerebral oxygenation to a high degree of sensitivity and specificity, to become a useful clinical tool, thresholds for cerebral ischemia need to be defined. This study has attempted to identify a quantifiable TOI threshold for ischemia in the adult brain.

METHODS

One hundred sixty-seven patients undergoing carotid endarterectomy were studied. The NIRO 300 was incorporated into an established multimodal monitoring system enabling observations of cerebral hemodynamic changes under highly controlled conditions. Changes in TOI (%DeltaTOI) on clamping the internal carotid artery were compared with intracranial blood flow (middle cerebral artery flow velocity) and cerebral function monitoring to identify and quantify periods of cerebral ischemia.

RESULTS

Significant correlation was seen between changes in middle cerebral artery flow velocity and DeltaTOI on clamping (r=0.74, P=0.0001). Thirty-one patients showed cerebral ischemia on internal carotid artery clamping as defined by a sustained fall in cerebral function monitoring. A threshold for %DeltaTOI of -13 was identified, above which no patients showed any evidence of ischemia on clamping. This threshold provided 100% sensitivity and 93.2% specificity for patients satisfying the preset criteria for cerebral ischemia.

CONCLUSIONS

These data demonstrate the potential to identify TOI-quantified thresholds for cerebral ischemia in the adult brain and thus improve the clinical use of near infrared spectroscopy. Our observations have defined a drop in TOI (13%) that can be adopted as a threshold for severe cerebral ischemia with high sensitivity and specificity.

Comparison of monitoring techniques for intraoperative cerebral ischemia

OBJECTIVE

To prospectively compare somatosensory evoked potentials, electroencephalography (EEG) and transcranial Doppler ultrasound (TCD) for detection of cerebral ischemia during carotid endarterectomy (CEA).

METHODS

Somatosensory evoked potentials and EEG recordings were attempted in 156 consecutive CEAs and TCD was also attempted in 91 of them. Recordings from all three modalities were obtained for at least 10 minutes before CEA, during CEA and for at least 15 minutes after CEA. Somatosensory evoked potentials peak-to-peak amplitude decrease of >50%, EEG amplitude decrease of >75%, and ipsilateral middle cerebral artery mean blood flow velocity (mean VMCAi) decrease >75% persisting for the entire period of internal carotid artery occlusion were individually considered to be diagnostic of cerebral ischemia. Clinical neurological examination was performed immediately prior to surgery and following recovery from general anaesthesia.

RESULTS

Somatosensory evoked potentials, EEG, and TCD were successfully obtained throughout the entire period of internal carotid artery occlusion in 99%, 95%, and 63% of patients respectively. Two patients (1.3%) suffered intraoperative cerebral infarction detected by clinical neurological examination and subsequent magnetic resonance imaging. Somatosensory evoked potentials accurately predicted intraoperative cerebral infarction in both instances without false negatives or false positives, EEG yielded one false negative result and no false positive results and VMCAi one true positive, four false positive and no false negative results. Transcranial Doppler ultrasound detection of emboli did not correlate with postoperative neurological deficits. Nevertheless the sensitivity and specificity of each test was not significantly different than the others because of the small number of disagreements between tests.

CONCLUSION

A >50% decrease in the cortically generated P25 amplitude of the median somatosensory evoked potentials, which persisted during the entire period of internal carotid artery occlusion, appears to be the most reliable method of monitoring for intraoperative ischemia in our hands because it accurately detected both intraoperative strokes with no false positive or false negative results.

Neurological Evaluation by Intraoperative Wake-up During Carotid Endarterectomy Under General Anesthesia

Although general anesthesia allows relief from stressors such as pain, discomfort, or anxiety for patients undergoing carotid endarterectomy, neurologic assessment is less reliable than under local anesthesia. We describe a unique anesthetic management strategy for carotid endarterectomy patients incorporating the advantages of both general and local anesthesia. The technique allows thorough assessment of neurologic function during carotid cross-clamping by intraoperative wake-up, and guarantees airway management by tracheal intubation.

Near Infrared Spectroscopy Monitoring During Carotid Endarterectomy: Which Threshold Value is Critical?

OBJECTIVES

Retrospectively to verify which decreasing percentage in regional oxygen saturation (rSO(2)) identified patients with good collateralisation during carotid artery cross clamp.

MATERIALS AND METHODS

During 594 endarterectomies under general anaesthesia the decreasing percentage from preclamp value to value detected in the first 2 min after clamping the CCA and/or ICA was calculated in real time. No temporary shunt was placed in any case. ROC analysis was performed to determine the optimal cut-off for rSO(2) decrease to identify the occurrence of neurological complications.

RESULTS

A cut-off of 11.7% was identified as optimal. Sensitivity and specificity were 75% (95% CI 71-78) and 77% (95% CI 74-80), respectively. The cut-off of 20% had a lower sensitivity (30%) and a higher specificity (98%) to identify patients with complications, with positive and negative predictive value of 37 and 98%, respectively.

CONCLUSIONS

The study suggest that a relative decrease in rSO(2) of <20% from preclamp to early cross clamp value has a high negative predictive value, i.e. if rSO(2) does non decrease more than 20%, ischemia by hypoperfusion is unlikely and a shunt should not be necessary. Moreover, a relative decrease >20% may not always indicate intraoperative neurological complications.

Evaluation of extracranial-intracranial arterial bypass function by using near-infrared spectroscopy

OBJECT

It has been reported that extracranial-intracranial (EC-IC) arterial bypass surgery can be useful in preventing stroke in patients with hemodynamic compromise. Little is yet known, however, regarding the extent to which the bypass contributes to maintaining adequate cerebral blood oxygenation (CBO) and its temporal changes following surgery. The authors evaluated bypass function repeatedly by using near-infrared spectroscopy (NIRS) after surgery.

METHODS

The authors investigated 30 patients who had undergone EC-IC bypass surgery. Single-photon emission computerized tomography revealed a decrease in regional cerebral blood flow (rCBF) and a lowered rCBF response to acetazolamide. Changes in CBO were evaluated in the sensorimotor cortex during compression of the anastomosed superficial temporal artery (STA). When decreases in oxyhemoglobin (HbO2) and total hemoglobin (Hb) concentrations were observed, the bypass was considered to have maintained CBO in the sensorimotor cortex given that decreases in HbO2 and total Hb indicate cerebral ischemic changes. The bypass maintained CBO immediately after surgery in 36.7% of patients (Group I, 11 patients) and at some time after surgery, mostly within 1 year, in 43.3% of patients (Group II, 13 patients); however, it did not maintain it throughout the follow-up period in 20% of patients (Group III, six patients). Note that the preoperative rCBF in patients in Groups I and II was lower than that in patients in Group III (p < 0.004). In fact, the preoperative rCBF predicted whether a bypass would maintain CBO at a cutoff value of 24.5 to 25 ml/100 g/min. Among Groups I and II, 18 patients demonstrated an increase in deoxyhemoglobin during STA compression. The preoperative rCBF in these cases was lower than that in the six remaining patients (p < 0.006). Note that the preoperative rCBF predicted the postoperative deoxyhemoglobin response at a cutoff value of 22.2 to 24 ml/100 g/min.

CONCLUSIONS

The EC-IC bypass surgery can maintain CBO immediately after surgery or gradually within 1 year when the preoperative rCBF is below 24.5 to 25 ml/100 g/min. Furthermore, bypass flow plays a critical role in maintaining an adequate CBO when preoperative rCBF is below 22.2 to 24 ml/100 g/min.

The effectiveness of regional cerebral oxygen saturation monitoring using near-infrared spectroscopy in carotid endarterectomy

Nineteen patients (20 operations) underwent elective carotid endarterectomy without arterial shunt. Carotid cross-clamping caused a significant decrease (from 61.2% to 49.5%, 19.1% decrease from the preclamp baseline) of the ipsilateral cerebral oxygen saturation and it increased to 65.6% after declamping. Cross-clamping also caused a significant decrease (from 2.9 Hz to 1.6 Hz) of the ipsilateral electroencephalogram main frequency and it increased to 3.6 Hz after declamping. Asymmetry of main frequency which was greater than 0.7 Hz was observed when that of oxygen saturation decreased more than 25% during cross-clamping. The reported data indicate that cerebral oxygen saturation less than 54-56.1% and its decrease more than 15.6-18.2% is found to be a predictor of neurologic compromise. In this study, the asymmetry of cerebral oxygen saturation more than 25% was also found to be a risk. Arterial shunt should be used in haemodynamically high risk cases.

Anesthesia for carotid endarterectomy

Patients presenting for carotid endarterectomy provide anesthesiologists with many challenges. These include optimization of cerebrovascular hemodynamics and oxygen balance, as well as minimizing myocardial risk. Fiscal pressures have encouraged the development of clinical pathways in many centers, with a remarkable trend towards decreased intensive care unit utilization and length of hospital stay. Anesthetic and surgical practices vary widely, but outcomes in these high-risk patients are usually excellent despite these differences. The potential for expanded indications for carotid endarterectomy and development of percutaneous treatment for carotid stenosis will provide neurovascular anesthesiologists with additional incentives to refine the anesthetic management of these patients.

Comparison of near-infrared spectroscopy and somatosensory evoked potentials for the detection of cerebral ischemia during carotid endarterectomy

BACKGROUND AND PURPOSE

We sought to assess the clinical value of regional cerebral saturation (rSO2) obtained by means of the cerebral oximeter INVOS 3100A (Somanetics) in comparison to monitoring of somatosensory evoked potentials (SEP) for the reliable detection of severe cerebral ischemia requiring shunt placement in the individual patient undergoing carotid surgery under general anesthesia.

METHODS

In 317 patients undergoing reconstructive surgery on the internal carotid artery, simultaneous recordings of SEP and rSO2 were obtained throughout the operation.

RESULTS

All 287 patients with preserved cortical SEP remained neurologically intact. Shunt placement was performed in 27 patients (9%) after flattening of cortical SEP during cross-clamping of the internal carotid artery. A stable rSO2 value just before cross-clamping and the lowest value after cross-clamping were registered, and the decrease was calculated. A statistically significant (P<0.01) decrease of rSO2 after cross-clamping could be found in patients without (64.9+/-8.3% to 60.9+/-9.9%) as well as in patients with consecutive loss of cortical SEP (65.8+/-9.1% to 56.1+/-13.4%). The difference of the decrease of rSO2 in both groups was highly significant (6.9+/-9.0% versus 15.6+/-14.0%; P<0.001). However, substantial interindividual variability of rSO2 and derived change of rSO2 did not allow the definition of a threshold value indicating need of shunt placement.

CONCLUSIONS

The reliability of SEP for the detection of clamp-related hypoperfusion has been reaffirmed. As long as rSO2 threshold values indicating critical cerebral ischemia are not defined, therapeutic interventions based on monitoring with the cerebral oximeter INVOS 3100A are not justified.