Monitoring during carotid surgery: somatosensory evoked potentials vs. carotid stump pressure

In the following prospective study of 125 carotid endarterectomies, we compared monitoring of somatosensory evoked potentials (SEPs) with carotid stump pressure (CSP) measurement in order to determine the efficacy of both methods in reliably predicting cerebral ischemia caused by cross-clamping of the carotid artery. A complete flattening of the cortical SEP was the sole criterion for selective shunting. Two patients suffered from transitory neurological deficits in the postoperative period. Both experienced complete disappearance of postcentral SEP components after carotid cross-clamping. In a further 10 cases, an intraoperative loss of SEP amplitudes occurred, but could be reversed by the insertion of a shunt or by induced hypertension. All of these patients showed a normal neurological examination postoperatively as did all of the patients with identifiable SEPs after cross-clamping. In all of the 12 patients with complete flattening of the cortical waveform, we found CSP levels less than 50 mm Hg. A further 61 patients had a CSP less than 50 mm Hg, but neither an intraoperative loss of SEP amplitudes nor postoperative neurological deficits were detected in any of these patients. We conclude that, in contrast to CSP, SEPs not only help to identify patients with insufficient collateral blood flow who benefit from specific cerebral protection, but also to avoid improper and hazardous application of these measures in patients with sufficient cerebral perfusion.     

Somatosensory evoked potentials in carotid surgery

During carotid surgery a monitoring device that will identify patients with inadequate cerebral perfusion and impending cerebral damage after carotid clamping is desirable. Such patients may benefit from cerebral protective measures, which should be applied selectively as their use can also lead to complications. METHODS. In order to evaluate the reliability of somatosensory evoked responses as a means of detecting patients with insufficient collateral perfusion after carotid cross clamping, a prospective study involving 482 operations for reconstruction of supraaortic vessels was performed. Somatosensory evoked potentials (SEPs) were recorded from a cervical (C2-Fz) and a parietal (C3'/C4'-Fz) electrode above the ipsilateral hemisphere following stimulation of the contralateral median nerve. RESULTS. In 22 procedures (4.6%) complete flattening of the cortical SEP occurred after carotid cross clamping. In 7 of 9 cases in which no indwelling shunt was used despite electrical silence neurological deficits were found postoperatively. The SEP amplitude was restored in 12 of the remaining 13 patients with complete loss of the SEP after shunt insertion. Only 3 of these patients demonstrated neurological impairment. During 460 operations evoked potentials were always present. Nevertheless, 5 neurological sequelae were noticed despite unchanged SEP after carotid artery clamping. All deficits, however, were caused by embolization and were unrelated to reduced blood flow after carotid cross clamping. CONCLUSIONS. Our results confirm the reliability of SEP monitoring for the detection of significant cerebral ischemia after carotid clamping. In absence of the cortical SEP immediate shunt placement is necessary to avoid neurological deficits. On the other hand, the risks attendant on indiscriminate cerebral support (embolism after shunt placement, cardiac ischemia due to induced hypertension) can be avoided in the presence of cortical potentials. This allows protection of the heart and the brain by anesthetic management and enables the surgeon to perform endarterectomy with no hurry, to avoid technical failure. SEP data may also be helpful in decision making on reoperation to look for sources of embolization. In conclusion, advanced monitoring by somatosensory evoked responses may help to improve the outcome of carotid surgery.     

Transcranial cerebral oxymetry during carotid endarterectomy: agreement between frontal and lateral probe measurements as compared with an electroencephalogram

Objective: Transcranial cerebral oximetry, which is considered a novel technique, was evaluated during carotid endarterectomy. For practical reasons, the use of a single probe attached to the forehead and overlying the territory of the anterior cerebral artery is recommended. Other monitoring systems (transcranial Doppler, electroencephalograms (EEG)) focus more on the territory of the middle cerebral artery. The aim of this study was to evaluate whether a probe in the frontal area is as representative for monitoring cerebral ischaemia during carotid cross-clamping as a probe in the lateral area. Design: Clinical prospective study. Materials: Sixty patients who underwent carotid endarterectomy were studied with continuous and simultaneous EEG and transcranial cerebral oximetry. Forty-three patients (72%) simultaneously underwent frontal and lateral transcranial cerebral oximetry. The lateral probe was only used in 17 patients. Methods: The percentage decrease of transcranial cerebral oximetry was calculated during cross-clamping. Using the EEG findings as the gold standard in order to detect cerebral ischaemia during carotid cross-clamping, the relationship with transcranial cerebral oximetry was described in terms of sensitivity, specificity and the area under the curve in a receiver operating characteristic curve. Results: The 95% confidence interval of the area under the curve of the receiver operating characteristic of the lateral probe was 0.61–1.00 and that of the frontal probe was 0.65–1.00; therefore there is virtually no difference between the two methods. In 18% of the cases the lateral transcranial cerebral oximetry was hindered by practical failures. Conclusion: Considering the lack of additional information and the practical problems experienced with the lateral probe, it was concluded that transcranial cerebral oximetry with a single frontal probe is a practical non-invasive monitoring system and is at least as representative for monitoring cerebral ischaemia during carotid cross-clamping as a lateral probe.     

Cerebral oximetry in patients undergoing carotid endarterectomy: preliminary results

Carotid endarterectomy (CEA) is an appropriate treatment for carotid occlusive disease. The risk of stroke during CEA ranges from 1.1% to 7.5%. Shunting is usually advised when severe ischemia during cross-clamping of the internal carotid artery is suspected. Routine use of an intraluminal shunt may increase the perioperative stroke rate. Popular and well documented methods of neurologic monitoring for ischemia during general anesthesia are electroencephalography (EEG) and transcranial Doppler ultrasonography (TCD) of the middle cerebral artery. The purpose of this prospective study was to compare cerebral oximetry using near infrared spectrophotometry (NIRS) with EEG and TCD. Preliminary data on 14 patients scheduled for elective carotid endarterectomy were included and a literature search was performed to correlate the findings. No postoperative neurologic events occurred. During carotid clamping there was a significant decrease in regional oxygen saturation (rSO2) but there was only a weak correlation with the decrease in mean Doppler flow (R = 0.74; P = 0.02) and no correlation with EEG changes (R = 0.49; P = 0.18). A useful rSO2 cut-off value predictive for cerebral ischemia could not be defined.     

Cerebral monitoring of somatosensory evoked potentials during carotid surgery: a review of 100 cases

The purpose of this study was to evaluate immediate and middle-term results of surgical carotid artery revascularization (CAR) with cerebral monitoring of intraoperative somatosensory evoked potentials (SEPs). Between 1998 and 2004, a total of 100 CARs in 86 patients were performed under general anesthesia with SEP monitoring. A shunt was inserted if SEP amplitude decreased by 50% or latency time increased by 10%. Immediate and middle-term results were analyzed retrospectively. The shunt insertion rate was 5%. Two transient ischemic attacks were observed, and one patient died postoperatively due to myocardial infarction. The cumulative stroke and death rate was 1% at 30 days. Intraoperative SEP monitoring with selective shunt placement can be used safely for carotid surgery. Randomized studies will be necessary to determine the respective indications for various cerebral monitoring techniques.     

Carotid endarterectomy monitored with transcranial Doppler.

Intraoperative transcranial Doppler monitoring of cerebral ischemia during carotid clamping under general anesthesia was done in 238 carotid artery operations, mostly endarterectomy. Depending on the severity of reduction of middle cerebral artery mean velocity, patients were classified as no, mild, or severe ischemia at clamping. With a carotid shunt, velocity was always in the "no ischemia" category during shunting. For patients with no ischemia, stroke was significantly lower without a shunt (2/175 no shunt versus 2/12 shunt). For mild ischemia, shunting did not affect the stroke rate (1/20 no shunt versus 0/9 shunt). For severe ischemia, strokes were less frequent with a shunt (4/9 no shunt versus 0/13 shunt). Intraoperative electroencephalogram predicted most, but not all severely ischemic cases. Carotid back pressure correlated with Doppler velocity, but transcranial Doppler was more helpful. Transcranial Doppler is a new and valuable technique in carotid surgery.     

Continuous monitoring to detect brain ischemia during carotid endarterectomy and aortic arch replacement by near infrared spectrophotometory--a case report

We report two cases in which continuous monitoring was used to detect brain ischemia by 8-channel electroencephalograph (EEG), transcranial Doppler (TCD) of middle cerebral blood flow velocities and near infrared spectrophotometric monitoring (NIR) of bifrontal area simultaneously. The symptom of brain ischemia was indicated by NIR and TCD but not by EEG following temporary cross-clamping of the common carotid artery during carotid endarterectomy. According to this sign we successfully used temporary shunt during CEA. On the other hand, these methods of monitoring did not show abnormal findings of cerebral blood flow disorders during aortic arch replacement. Nevertheless, neurologic disorders were complicated postoperatively. In conclusion, these methods monitor carotid artery blood flow but not vertebral artery blood flow.     

Pre- and intraoperative transcranial doppler: Prediction and surveillance of tolerance to carotid clamping

We report 91 patients (mean age 70 years) operated upon, prospectively for a total of 100 carotid revascularizations (nine bilateral). Eighty-five of these patients had pre-, intra-, and postoperative transcranial Doppler investigations. Preoperatively, these 85 patients (92 procedures) were classified into two groups based on the results of their Doppler examinations: Group A (65 patients, 72 procedures), those who did not require an intraoperative indwelling shunt and Group B (20 patients, 20 procedures), those who did. The shunt was inserted only when the mean stump (back) pressure was less than 50 mmHg after cross-clamping. Group A all had satisfactory collaterality with a functional anterior and one or two posterior communicating arteries. Group B had no communicating arteries (anterior or posterior) identified by transcranial Doppler. In 17 of 20 patients in this group, the stump pressure was less than 50 mmHg and a shunt was placed. The overall prediction based on Doppler examination of whether or not patients would need a shunt during operation for the two groups A and B (i.e., 92 procedures) was correct in 95.6% (88/92) of cases. Moreover, six hemodynamically significant stenoses (four in the cavernous portion, two in the middle cerebral artery) were disclosed. Sensitivity and specificity of transcranial Doppler as correlated with arteriographic findings were 70 and 90%. Preoperative transcranial Doppler can measure the velocities of the principal cerebral arteries and the collateral capacity of the circle of Willis, and can forecast tolerance to carotid cross-clamping. Intraoperatively, the velocity of flow in the middle carotid artery was correlated with stump pressure, which allowed for surveillance of the shunt.Presented at the Annual Meeting of the Société de Chirurgie Vasculaire de Langue Française, May 18–19, 1990, Nancy, France.     

Monitoring of somatosensory evoked potentials during surgical procedures on the thoracoabdominal aorta. I. Relationship of aortic cross-clamp duration, changes in somatosensory evoked potentials, and incidence of neurologic dysfunction

To determine if intraoperative monitoring of somatosensory evoked potentials detects spinal cord ischemia, we subjected 21 dogs to aortic cross-clamping distal to the left subclavian artery. Group I animals (short-term studies, n = 6) demonstrated decay and loss of somatosensory evoked potentials at 8.5 +/- 1.1 minutes after aortic cross-clamping. During loss of somatosensory evoked potentials, significant decreases in spinal cord blood flow occurred in cord segments below T6. Significant reactive hyperemia occurred without normalization of somatosensory evoked potentials after reperfusion. Fifteen Group II animals (long-term studies) were studied to determine the relationship between duration of spinal cord ischemia (evoked potential loss) and subsequent incidence of paraplegia. Extension of aortic cross-clamping for 5 minutes after loss of somatosensory evoked potentials in six dogs resulted in no paraplegia (mean cross-clamp time 12.7 +/- 0.6 minutes). Prolongation of aortic cross-clamping for 10 minutes after evoked potential loss in nine dogs (mean cross-clamp time 17.6 +/- 0.6 minutes) resulted in a 67% (6/9) incidence of paraplegia 7 days postoperatively (p = 0.02 versus 10 minutes of aortic cross-clamping). These findings demonstrate that simple aortic cross-clamping uniformly results in spinal cord ischemia and that such ischemia is detectable by monitoring of somatosensory evoked potentials. Duration of ischemia, as measured by the time of evoked potential loss during the cross-clamp interval, is related to the incidence of postoperative neurologic injury.     

Is transcranial Doppler useful in the detection of internal carotid artery cross-clamp intolerance?

The aim of this study was to test the hypothesis that a drop in the systolic blood flow velocity in the middle cerebral artery of 70% or more, measured by transcranial Doppler, is a better criteria in the detection of cross-clamp intolerance than electroencephalogram (EEG) and somatosensory evoked potential (SSEP) monitoring. After exclusion of patients with a recent stroke, urgent procedures and combined procedures, a transcranial Doppler with compression test was scheduled in 85 patients. In 13 patients the drop was 70% or more and in these patients a transcranial Doppler was also performed during the reconstruction of the internal carotid artery (the study group) under general anaesthesia. A shunt was used because of EEG and SSEP abnormality in one patient. No changes were observed in the remaining patients and no intraoperative strokes were seen. The transcranial Doppler monitoring was unreliable in three patients. During cross-clamp, the systolic blood flow velocity in the middle cerebral artery dropped less than 70% in four and 70% or more in six patients. It is concluded that using a drop of 70% or more of the systolic blood flow velocity in the middle cerebral artery during internal carotid artery cross-clamp, as an indicator of cross-clamp intolerance, will lead to unnecessary shunting.     

Monitoring of somatosensory evoked potentials during extracranial revascularization

Intraoperative somatosensory evoked potentials (SEPs) were measured in 17 patients during 21 extracranial revascularization and related procedures. The operations included 13 carotid endarterectomies (CEAs), two cervical internal carotid ligations, one vertebral artery (VA) clipping, one VA-common carotid artery (CCA) transposition, and four temporary balloon occlusion tests (TBOTs). Three of the 13 CEAs (23%) showed reduced amplitude and delayed latency of primary cortical SEPs during clamping of the carotid artery, followed by their recovery after emplacement of the internal shunt. Flattening of SEPs during clamping of the CCA was observed in the case of VA-CCA transposition; however, SEPs returned to normal immediately after insertion of a balloon indwelling shunt into the CCA. One of the four TBOTs showed alteration of SEPs during balloon occlusion of the subclavian artery proximal to the origin of the VA. In the others, SEPs remained stable during the entire procedure. Only one transient intraoperative ischemic complication was encountered among the cases of CEA. It was detected through flattening of SEPs, which led to the discovery of an internal shunt obstruction. Carotid stump pressure was also measured in 12 CEAs and two TBOTs, and seven of these 14 had pressure less than or equal to 50 mmHg. Four of the seven had carotid stump pressure less than or equal to 30 mmHg, and three of these four also showed altered SEPs. SEPs remained stable if the collateral flow was sufficient during vascular occlusion and showed obvious alteration when the blood flow was reduced to below the threshold. The authors conclude that monitoring of SEPs during extracranial revascularization is very useful.     

Monitoring of somatosensory evoked potentials during surgical procedures on the thoracoabdominal aorta. IV. Clinical observations and results

Thirty-three patients undergoing operations on the descending thoracic or thoracoabdominal aorta were monitored to evaluate causes and effects of spinal cord ischemia as manifested by changes in somatosensory evoked potentials. Maintenance of distal aortic perfusion pressure (greater than 60 mm Hg) by either shunt or bypass techniques in 17 patients resulted in preservation of somatosensory evoked potentials and a normal postoperative neurologic status, irrespective of the interval of thoracic cross-clamping (range 23 to 105 minutes). In 16 other patients in whom cross-clamp time ranged from 16 to 124 minutes, evoked potential loss was observed because of failure to provide distal perfusion (n = 8), inadequate maintenance of distal perfusion pressure (less than 60 mm Hg) despite shunt/bypass (n = 6), or interruption of critical intercostal arteries (n = 2). Incidence of paraplegia in the entire group was 15.1% (5/33) and was limited to only those patients in whom evoked potential loss occurred (5/16, 31.2%) (p = 0.02). Loss of somatosensory evoked potentials for more than 30 minutes resulted in a 71.2% (5/7) incidence of paraplegia, whereas no neurologic deficit was noted in patients (0/26) in whom evoked potential loss was either prevented or limited in duration to 30 minutes (p less than 0.001 versus loss for more than 30 minutes). Intraoperative monitoring of somatosensory evoked potentials is a sensitive indicator of spinal cord ischemia. Simple aortic cross-clamping, failure to maintain distal perfusion pressure above 60 mm Hg, and inability to reimplant critical intercostals in a timely fashion result in a high rate of paraplegia if duration of spinal cord ischemia as measured by somatosensory evoked potentials exceeds 30 minutes. Routine evoked potential monitoring during thoracoabdominal procedures appears useful in assessing the adequacy of spinal cord perfusion. Furthermore, it can alert the surgeon to the necessity for critical intercostal artery reimplantation as well as the need for adjustment or regulation of distal aortic perfusion.     

Does anatomical completeness of the circle of Willis correlate with sufficient cross-perfusion during unilateral cerebral perfusion?

OBJECTIVES: The aim of the study was to evaluate the role of anatomical completeness of the circle of Willis for sufficient brain perfusion during unilateral cerebral perfusion and the methodology of the preoperative and intraoperative functional assessments of adequate cross-perfusion. METHODS: This prospective observational study included all elective patients (99) who underwent elective open arch surgery (hemiarch in 74 and arch replacement in 25 patients, respectively) at our institution between September 2004 and September 2006. Preoperative neuro-vascular evaluation included color-coded duplexsonography of the extracranial arteries, cranial CT angiography, and transcranial sonography. A functional test of cerebral cross-perfusion was performed during cross-clamping of the common carotid artery during cannulation by transcranial Doppler, electroencephalography and measurement of somatosensory evoked potentials. These examinations, which were completed through measurement of arterial pressure in both radial arteries, also served as an intraoperative assessment of cerebral perfusion during surgery. During mild hypothermic (30 degrees C) circulatory arrest with a mean duration of 18 min (range, 7-70) brain protection using unilateral cerebral perfusion was performed in all patients. RESULTS: As assessed in preoperative CT angiography, the circle of Willis was complete in only 59 patients. Eighteen patients showed a singular abnormal location within the circle of Willis, 13 patients presented with abnormalities within the posterior communicating arteries on both sides, and 9 patients within the anterior and posterior communicating arteries. Nevertheless, functional tests during carotid artery cross-clamping as well as intraoperative cerebral monitoring including transcranial Doppler showed no pathology in any patient, and only one patient with severe aortic valve calcification suffered from embolic minor stroke after surgery. CONCLUSIONS: The anatomical status of the circle of Willis assessed with cranial CT angiography does not correlate with functional and intraoperative tests examining the cerebral cross-perfusion. The authors do not recommend cranial CT angiography as a preoperative standard examination before open arch surgery in which unilateral cerebral perfusion is scheduled.     

Significant correlation between cerebral oximetry and carotid stump pressure during carotid endarterectomy

Limited information on a correlation between carotid stump pressure and cerebral oximetry changes associated with cross-clamping of carotid vessels during carotid endarterectomy (CEA) prompted us to prospectively evaluate 38 consecutive CEAs in 37 patients. The authors used the INVOS-4100 cerebral oximeter to measure cerebral oximetry (cerebral oxygen saturation) before (t1) and after (t2) cross-clamping along with carotid stump pressure. All patients had CEA under general anesthesia with the routine use of a Javid shunt. Cross-clamping (t1 vs. t2) resulted in statistically significant changes (p < 0.0001) on the operated side of 6.03 units or a percent change of 9.2% when analyzed using the nonparametric signed-rank test. The nonoperated side had insignificant change (p = 0.71). Spearman correlation analysis revealed significant correlation (r = -0.63) between cerebral oximetry changes on the operated side and carotid stump pressure such that a larger change in cerebral oximetry due to cross-clamping was strongly and significantly correlated with lower carotid stump pressure. Using regression analysis, stump pressures of 25 and 50 mm Hg were predicted by cerebral oximetry changes of 28.5 or 8.8 units, respectively. This is equivalent to a percent change from baseline (t1) of 41.1% or 13.1%, respectively. Taken together, these findings suggest that cerebral oximetry can be used as an alternative to carotid stump pressure to provide noninvasive, inexpensive, and continuous real-time monitoring during CEA.     

Somatosensory-evoked potentials during carotid artery surgery: experience in 400 operations

A prospective study was undertaken to determine the efficacy of monitoring somatosensory-evoked potentials (SEP) during carotid artery surgery in predicting a new ischemic neurologic deficit. Three hundred seventy-six patients underwent 400 reconstructions of the internal carotid artery. The mortality rate of the entire series was 0.8%. In 383 procedures, SEP amplitudes were always present during cross-clamping of the internal carotid artery. In spite of that, three neurologic deficits occurred, but all were associated with technical failures and not related to clamping ischemia. Complete loss of SEP amplitudes was noted in 17 procedures. Five of seven patients without an indwelling shunt showed a neurologic deficit after surgery, whereas shunt insertion in 10 resulted in three neurologic deficits. It is concluded that at present SEP recording is an accurate monitoring method in detecting clamping-related cerebral ischemia during carotid artery surgery.     

Assessment of Early Brain Damage in Carotid Endarterectomy: Evaluation of S-100B Serum Levels and Somatosensory Evoked Potentials in a Pilot Study

The release of the neuronal protein S-100B into the circulation has been suggested as an early indication of cellular brain damage. The objective of this prospective pilot study was to determine S-100B serum levels in patients undergoing cross-clamping during carotid endarterectomy (CEA) and to correlate the results with the monitoring of somatosensory evoked potentials (SSEP) and the neurological short-term outcome. Arterial blood samples of 21 patients were drawn before oral intubation, cross-clamping, and unclamping, as well as before extubation and 6 hours later. Recording of SSEP was obtained during carotid occlusion and reperfusion. If loss of SSEP appeared, cerebral ischemia was assumed and an intraluminal shunt was placed. During cross-clamping, S-100B serum levels of 14 patients increased significantly from 0.05 ng/ml to 0.21 ng/ml, but returned to baseline levels after unclamping. In 5 cases, loss of SSEP amplitudes occurred but was reversed by the shunt insertion. No significant differences of S-100B serum values, neurological examination, and carotid duplex surveillance became obvious in this group when compared to the patients with undisturbed SSEP. However, 2 patients with complete disappearance of postcentral SSEP components suffered from neurological deficits in the postoperative period. S-100B serum levels remained highly elevated 6 hours after extubation (0.78 ng/ml and 0.41 ng/ml) compared to the baseline values (0.15 ng/ml and 0.07 ng/ml). During CEA a transitory increase of the S-100B serum levels appears to present an impairment of the blood–brain barrier integrity without any neurological deficits. In contrast, persistently elevated S-100B serum levels seem to be associated with transient loss of SSEP and development of neurological deficits.     

Cerebral Ischemia during Carotid Artery Cross-Clamping: Predictive Value of Phase-Contrast Magnetic Resonance Imaging

The goal of this prospective study was to determine the utility of preoperative cerebral magnetic resonance imaging (MRI) in predicting cerebral ischemia during carotid artery cross-clamping for endarterectomy. Between January 2000 and December 2003, a total of 121 patients (95 men, 26 women) underwent three-dimensional phase-contrast MRI to assess collateral function prior to carotid endarterectomy. During regional anesthesia, patients were monitored to detect ischemic events and their timing in relation to cross-clamping and to determine mean intraoperative arterial pressure. These findings were then correlated with the collateral variations observed in the circle of Willis on preoperative MRI. Patients were classified into three groups according to neurological tolerance: normal tolerance (n = 106), immediate severe deficit (n = 9), and late deficit associated with arterial hypotension (n = 6). In the second group, a significant correlation was found between the absence of collateral circulation and neurological deficit (p < .0001). These results indicated that three-dimensional phase-contrast MRI is useful for predicting cerebral ischemia during carotid cross-clamping and selecting indications for shunting. Absence of visible collaterals of the circle of Willis on MRI is significantly predictive of early ischemia and an indication for systematic shunt placement.     

Incidence,timing, and causes of cerebral ischemia during carotid endarterectomy with regional anesthesia

Purpose: Controversy exists regarding the best technique to identify cerebral ischemia during carotid endarterectomy (CEA). Regional anesthesia allows continuous evaluation of neurologic function and therefore can help determine the incidence, timing, and causes of cerebral ischemia. Methods: The timing and clinical manifestations of any neurologic event during CEA and as long as 30 days afterward was determined by review of operative reports, hospital charts, and outpatient records of consecutive patients who underwent CEA under regional anesthesia over a 68-month period. Results: Two hundred patients underwent CEA; indications were asymptomatic stenosis >60% in 25%, transient ischemic attack with stenosis >50% in 52%, and prior stroke with stenosis >50% in 23%. Eight patients (4%) were converted to general anesthesia for nonischemic reasons. Of the remaining 192 patients, 183 (95.5%) underwent the procedure with regional anesthesia and no shunt, 2% had cerebral ischemia and underwent shunt placement, and 2.5% had cerebral ischemia, were converted to general anesthesia, and underwent shunt placement. Cerebral ischemia developed in nine patients after carotid cross-clamping, manifested by loss of consciousness in four, confusion in two, dysarthria and confusion in one, and decreased contralateral motor strength in two. Immediate cerebral ischemia developed in four of the nine patients within 1 minute of cross-clamping; all four underwent shunt placement. In five of the nine patients, cerebral ischemia occurred between 20 and 30 minutes after cross-clamping; all occurred during relative intraoperative hypotension (average reduction of 35 mm Hg in the systolic pressure). All awake patients in whom ischemic symptoms developed immediately regained and maintained normal neurologic function with shunt placement. Five of 26 patients (19%) with contralateral occlusion required a shunt; none had postoperative ischemia. The mean carotid cross-clamp time was 27 minutes. Postoperative (30 day) complications included a 0.5% stroke rate, a 0.5% rate of postoperative transient ischemic attack, a 0.5% rate of worsening of preexisting acute stroke, and a 0.5% rate of myocardial infarction (no deaths). Of the nine patients who had intraoperative ischemic changes, none had a postoperative neurologic deficit; the three patients who had postoperative neurologic changes had no intraoperative ischemic symptoms. Conclusions: CEA with regional anesthesia allows continuous neurologic monitoring and can be performed safely even when contralateral occlusion coexists; intraoperative shunting for ischemia is necessary in 4.5% of all cases and in 19% of patients with contralateral occlusion. Intraoperative ischemia was flow-related in our patients; it occurred early from ipsilateral carotid clamping and late from reduced collateral flow as a result of hypotension. Monitoring should be continued throughout cross-clamping to identify late cerebral ischemia. Postoperative cerebral ischemia is not associated with intraoperative ischemia, if corrected. (J Vasc Surg 1998;27:329-37.)     

Combined carotid endarterectomy, innominate artery reconstruction, and coronary artery bypass grafting: Case report

Neurologic injury is one of the most devastating complications of combined carotid and cardiac procedures. Although the cause of the deficit is usually embolic, the exact cause is often not apparent at the time of surgery. We present a complex case of combined carotid endarterectomy, innominate artery reconstruction, and coronary artery bypass procedures in which intraoperative monitoring with somatosensory evoked potentials and transcranial Doppler ultrasonography combined with postoperative acetazolamide single photon emission computed tomographic scans was used to correlate intraoperative events with cerebral activity and functional results. Although computed tomographic scan, magnetic resonance imaging, and clinical evaluation were negative for any evidence of stroke, the patient exhibited subtle postoperative changes in neuropsychologic function. These changes were correlated with intraoperative microemboli detected by transcranial Doppler monitoring, and postoperative acetazolamide single photon emission computed tomographic scanning, which revealed bilateral cortical defects. (J Vasc Surg 1996;24;1017-21.)     

Accuracy of cerebral monitoring in detecting cerebral ischemia during carotid endarterectomy: a comparison of transcranial Doppler sonography, near-infrared spectroscopy, stump pressure, and somatosensory evoked potentials

BACKGROUND: This study compares the accuracy of cerebral monitoring systems in detecting cerebral ischemia during carotid endarterectomy. METHODS: The authors compared transcranial Doppler sonography (TCD), near-infrared spectroscopy (NIRS), stump pressure (SP) measurement, and somatosensory evoked potentials (SEP) in 48 patients undergoing carotid surgery during regional anesthesia. Cerebral ischemia was assumed when neurologic deterioration occurred. During clamping, the minimum mean middle cerebral artery velocity (TCD(min)), its percentage change (TCD%), the minimum regional saturation of oxygen (NIRS(min)), its percentage change (NIRS%), the mean SP, and the changes of SEP amplitude were recorded. To analyze the corresponding sensitivity and specificity of each parameter, the authors performed receiver operating characteristic analysis. RESULTS: Neurologic deterioration occurred in 12 patients. SP and NIRS were successfully performed in all patients. TCD monitoring was not possible in 10 (21%); SEP was not possible in 2 patients (4%). All parameters provided the ability to distinguish between ischemic and nonischemic patients. TCD% and NIRS% showed significantly better discrimination than TCD(min) and NIRS(min) (P < 0.05). The highest area under the curve (AUC) was found for TCD% (AUC = 0.973), but there was no significant difference compared with NIRS% (AUC = 0.905) and SP (AUC = 0.925). The lowest AUC was found for SEP (AUC = 0.749), which was significantly lower than that for TCD%, NIRS%, and SP. CONCLUSIONS: TCD%, NIRS%, and SP measurement provide similar accuracy for the detection of cerebral ischemia during carotid surgery. Lower accuracy was found for SEP monitoring. Because of the high rate of technical difficulties (21%), TCD monitoring was the least practical of the investigated monitoring devices.