Stump pressure, the contralateral carotid artery, and electroencephalographic changes

Intraoperative middle cerebral artery pressure measurements during superficial temporal artery to middle cerebral artery bypass procedures in patients with cerebral atherosclerotic disease

OBJECTIVE

No previous study has monitored middle cerebral artery (MCA) pressure during the superficial temporal artery (STA)-MCA bypass procedure for cerebral atherosclerotic disease. In this paper, the authors describe their method of monitoring MCA pressure and report their initial data on intraoperative MCA pressure and its relationship with hemodynamics prior to and after the bypass procedures.

METHODS

The results from a total of 39 revascularization procedures performed between 2004 and 2014 were analyzed. The patient group included 27 men and 12 women, and their mean age at surgery was 67.6 years (range 39–83 years). The authors investigated the MCA pressure via the STA during STA-MCA bypass procedures. After one branch of the STA was anastomosed to the MCA, the other branch was connected to an arterial line, and a clip was placed temporally on the main STA trunk to monitor the pre-anastomosis MCA pressure. Simultaneously, the radial artery (RA) pressure was determined before removing the temporal clip to measure the post-anastomosis MCA pressure. The relationship between MCA pressures and single photon emission computed tomography findings and the risk factors for hyperperfusion after STA-MCA bypass were analyzed.

RESULTS

The MCA/RA (%) pressure was significantly correlated with that of the resting stenotic/normal side cerebral blood flow (CBF) ratio (%) in the linear regression analysis (slope 1.200, r2 = 0.3564, F = 20.49, p < 0.0001). The intraoperative MCA pressure was 39.3% of RA pressure in patients with Powers' Stage 2 cerebral atherosclerotic disease. After 1 branch of the STA was anastomosed, the intraoperative MCA pressure increased to 75.3% of the RA pressure. The rate of increase in pressure was significantly correlated with the increase in the STA diameter in the linear regression analysis (slope 2.59, r2 = 0.205, F = 9.549, p = 0.0038). Hyperperfusion occurred in 2 cases. When mean values for these 2 patients were compared with those for the 37 patients without hyperperfusion, significant differences were found in the stenotic/normal side CBF ratio (p = 0.0001), pre-anastomosis MCA pressure (p = 0.02), rate of increase in pressure (p = 0.02), pre-anastomotic MCA/RA pressure ratio (p = 0.01), vascular reserve (p = 0.0489), and STA diameter (p = 0.0002).

CONCLUSIONS

The measurement of intraoperative MCA pressure may be a useful technique to assess cerebral perfusion and for predicting the risk of hyperperfusion. Monitoring MCA pressure is recommended during STA-MCA bypass procedures for atherosclerotic disease.

Monitoring cerebral ischemia during carotid endarterectomy and stenting

Current therapy for carotid stenosis mainly includes carotid endarterectomy and endovascular stenting, which may incur procedure-related cerebral ischemia. Several methods have been employed for monitoring cerebral ischemia during surgery, such as awake neurocognitive assessment, electroencephalography, evoked potentials, transcranial Doppler, carotid stump pressure, and near infrared spectroscopy. However, there is no consensus on the gold standard or the method that is superior to others at present. Keeping patient awake for real time neurocognitive assessment is effective and essential; however, not every surgeon adopts it. In patients under general anesthesia, cerebral ischemia monitoring has to rely on non-awake technologies. The advantageous and disadvantageous properties of each monitoring method are reviewed.

Shunting during carotid endarterectomy

BACKGROUND

The use of shunting during carotid endarterectomy (CEA) is controversial. While some surgeons advocate routine shunting, others prefer selective shunting or no shunting. Several large series have documented excellent results of CEA with routine shunting or without shunts. Others reported similar results with selective shunting using transcranial Doppler (TCD), electroencephalogram (EEG) monitoring, carotid stump pressure (SP), cervical block anesthesia (CBA), and somatosensory evoked potential (SSEP). In this study, we review the available evidence supporting shunting, nonshunting, and selective shunting during CEA.

METHODS

An electronic PubMed/MEDLINE search was conducted to identify all published CEA studies between January 1990 and December 2010, that analyzed the perioperative outcome of routine shunting, routine nonshunting, routine versus selective shunting, selecting shunting versus avoiding a shunt, and selective shunting based on EEG, TCD, SP, CBA, and SSEP.

RESULTS

The mean reported perioperative stroke rate for CEAs with routine shunting was 1.4% and for routine nonshunt was 2%. Meanwhile, the mean perioperative stroke rates for selecting shunting were 1.6% using EEG, 4.8% using TCD, 1.6% using SP, 1.8% using SSEP, and 1.1% for CBA. Similar results were noted for perioperative stroke and death rates.

CONCLUSIONS

The use of routine shunting and selective shunting was associated with a low stroke rate. Both methods are acceptable, and the individual surgeon should select the method with which they are more comfortable.

POSTCAROTID ENDARTERECTOMY CEREBRAL HYPERPERFUSION CAN BE PREVENTED BY MINIMIZING INTRAOPERATIVE CEREBRAL ISCHEMIA AND STRICT POSTOPERATIVE BLOOD PRESSURE CONTROL UNDER CONTINUOUS SEDATION

OBJECTIVE

Cerebral hyperperfusion syndrome is a major complication after carotid endarterectomy (CEA). We investigated whether our strategy of minimizing intraoperative cerebral ischemia and strict postoperative blood pressure control under continuous sedation prevented postoperative hyperperfusion.

METHODS

Eighty consecutive patients undergoing CEA were studied. A shunt was used in all patients during CEA. All patients were managed postoperatively under continuous sedation for as long as 48 hours on the basis of the regional cerebral blood flow (rCBF) measured immediately after CEA. Postoperative hyperperfusion was assessed, on the basis of the cerebral blood flow study under sedation (propofol) after CEA, either as a greater than 30% increase in rCBF compared with the contralateral side, or a greater than 100% increase in the corrected rCBF (calculated from percentage reduction of the contralateral rCBF induced by propofol) compared with preoperative values.

RESULTS

No patient developed cerebral hyperperfusion syndrome. Postoperative hyperperfusion was found at very low rates (2.5% in the middle cerebral artery territory and 1.3% in the anterior cerebral artery territory by definition 1, and 0% in both territories by definition 2). Ratios of regional oxygen saturation after internal carotid artery clamping to preclamp baseline values were greater than 0.9 in 78 of 80 patients, indicating very mild intraoperative cerebral ischemia. Parameters related to cerebral ischemia during CEA, such as regional oxygen saturation, internal carotid artery cross-clamping duration, and stump pressure (index), did not affect the incidence of postoperative hyperperfusion.

CONCLUSION

The present study suggests that minimizing intraoperative cerebral ischemia using a shunt, followed by strict postoperative blood pressure control under continuous sedation, can prevent post-CEA hyperperfusion.

Prospective evaluation of electroencephalography, carotid artery stump pressure, and neurologic changes during 314 consecutive carotid endarterectomies performed in awake patients

OBJECTIVE

This study attempted to correlate neurologic changes in awake patients undergoing carotid endarterectomy (CEA) under cervical block anesthesia (CBA) with electroencephalography (EEG) and measurement of carotid artery stump pressure (SP).

METHODS

Continuous EEG and SP monitoring was measured prospectively in 314 consecutive patients undergoing CEA between April 1, 2003, and July 30, 2006, under CBA. Indications for CEA were asymptomatic 70% to 99% internal carotid artery stenosis in 242 (77.1%), transient ischemic attacks (including transient monocular blindness) in 45 (14.3%), and prior stroke in 27 (8.6%). Mean common carotid artery pressure before clamping, mean SP after carotid clamping, and intraarterial pressure were continuously monitored in all patients. An indwelling shunt was placed when neurologic events (contralateral motor weakness, aphasia, loss of consciousness, or seizures) occurred, regardless of SP or EEG changes.

RESULTS

Shunt placement was necessary because of neurologic changes in 10% (32/314) of all CEAs performed under CBA. Only 3 patients (1.4%) of 216 required shunt placement if SP was 50 mm Hg or more, vs 29 (29.6%) of 98 if SP was less than 50 mm Hg (P < .00001; sensitivity, 29.8%; specificity, 98.6%). In patients with SP of 40 mm Hg or more, 7 (2.6%) of 270 required shunt placement, vs 25 (56.8%) of 44 if SP was less than 40 mm Hg (P < .00001; sensitivity, 56.8%; specificity, 97.4%). Ischemic EEG changes were observed in 19 (59.4%) of 32 patients (false-negative rate, 40.6%) requiring shunt placement under CBA. Three patients had false-positive EEG results and did not require shunt placement (false-positive rate, 1.0%). The perioperative stroke/death rate was 4 (1.2%) in 314. All strokes occurred after surgery and were unrelated to cerebral ischemia or lack of shunt placement.

CONCLUSIONS

Ten percent of patients required a shunt placement during CEA under CBA. Shunt placement was necessary in 56.8% of patients with SP less than 40 mm Hg. EEG identified cerebral ischemia in only 59.4% of patients needing shunt placement, with a false-positive rate of 1.0% and a false-negative rate of 40.6%. Both SP and EEG as a guide to shunt placement have poor sensitivity. Intraoperative monitoring of the awake patients under regional anesthesia (CBA) is the most sensitive and specific method to identify patients requiring shunt placement.

Correlation of carotid artery stump pressure and neurologic changes during 474 carotid endarterectomies performed in awake patients

PURPOSE

A carotid artery stump pressure (SP) of < 50 mm Hg and abnormal electroencephalography (EEG) changes have been suggested as indications for selective shunting in patients undergoing carotid endarterectomy (CEA) under general anesthesia. We attempted to determine the optimal SP threshold that correlated with neurologic changes in awake patients undergoing CEA using cervical block anesthesia (CBA) and performed a cost comparison with EEG monitoring.

METHODS

Between July 1, 1995, and December 31, 2004, SP was measured during 474 CEAs performed under CBA by inserting a 19-gauge butterfly needle into the common carotid artery. A saline-filled intravenous bag in the patient's contralateral hand was connected to pressure tubing to generate waveforms with hand squeezing that could be visualized on a monitor. Systemic pressure was maintained approximately 10 mm Hg higher than baseline. Accurate SPs were confirmed by the finding of flatline waveforms after internal carotid artery clamping. Selective shunting was performed when neurologic changes occurred (aphasia, inability to squeeze the contralateral hand, decreased consciousness), regardless of SP. During this same period, 142 patients underwent CEA using GA, and SP was also measured.

RESULTS

Shunting was necessary because of neurologic changes in 7.2% (34/474) of all CEAs performed using CBA: 0.9% (3/335) with SPs > or = 50 mm Hg systolic vs 1.0% (4/402) with SPs > or = 40 mm Hg systolic, and 22% (31/139) with SPs < 50 mm Hg systolic vs 42% (30/72) with SPs < 40 mm Hg systolic. If these 474 CEAs had been performed using GA, shunts would have been used in 29% (139/474) of patients for a SP < 50 mm Hg systolic vs 15% (72/474) for a SP < 40 mm Hg systolic. In patients not shunted, the perioperative stroke/death rate was 1.2% in patients (4/332) with SPs > or = 50 mm Hg vs 1.0% (4/398) with SPs > or = 40 mm Hg. Three of the four strokes occurred > 24 hours postoperatively and were unrelated to lack of shunting and ischemia. There was no significant difference in the percentage of patients with SPs > or = 50 mm Hg who underwent CEA using CBA (70%, 335/474) vs GA (67%, 96/142) during this time period. At our hospital, charges for SPe measurement, including anesthesia charges and tubing, were 229 dollars per case vs 3439 dollars per case for EEG monitoring. Use of SP measurements in these 474 patients would have resulted in reduced charges of 1,521,540 dollars compared with EEG monitoring if CEA had been performed under GA.

CONCLUSION

Using 40 mm Hg systolic as a threshold, the need for shunting (15%) and the false-negative rate (1.0%) for SP in our series were equivalent to the results of EEG monitoring during CEA reported in the literature. However, charges for SP measurements are dramatically lower compared with EEG monitoring. Our results suggest that a carotid artery SP > or = 40 mm Hg systolic may be considered as an equally reliable but more cost-effective method to predict the need for carotid shunting during CEA under GA compared with EEG monitoring, but further investigation is warranted.

Carotid endarterectomy with routine electroencephalography and selective shunting: Influence of contralateral internal carotid artery occlusion and utility in prevention of perioperative strokes

OBJECTIVE

Carotid endarterectomy (CEA) is associated with a risk of cerebral ischemia during carotid clamping, particularly in the face of contralateral internal carotid artery (ICA) occlusion. We examined the results of CEA with continuous electroencephalography in patients without and with contralateral ICA occlusion.

DESIGN AND SETTING

We reviewed 564 primary CEAs with routine electroencephalography and general anesthesia performed between April 1, 1989, and March 31, 1999, in a community teaching medical center. Main outcome measures were perioperative stroke, temporary lateralizing neurologic deficit, and death. Shunts were placed primarily for significant electroencephalographic changes after carotid clamping but also selectively for contralateral ICA occlusion, prior stroke, or surgeon choice. CEA was performed for asymptomatic disease in 35% of cases.

RESULTS

Significant electroencephalographic changes occurred in 16% versus 39% (P <.001) and shunts were placed in 13% versus 55% (P <.001) of patients with patent (n = 507) versus occluded contralateral ICA (n = 57), respectively. The fraction of CEAs with significant electroencephalographic changes during clamping was stable, but shunt use declined slightly over time as our confidence in electroencephalography increased. Patches were placed more often (86% versus 65%; P =.002), but other operative details were similar when the contralateral ICA was occluded. Five early (30 days) strokes (0.9%) and eight early temporary postoperative neurologic events (1.4%) occurred, all ipsilateral to CEA and all after the patient left the operating room with none in patients with contralateral ICA occlusion. Two perioperative deaths occurred, one in a patient without and one in a patient with contralateral ICA occlusion. Neither of these deaths was related to ipsilateral stroke. No increase in stroke rate with decreased shunt use over time was seen.

CONCLUSION

Routine use of electroencephalography was associated with apparent complete elimination of intraoperative strokes and less than 1% risk of perioperative strokes. These observations appear to be true even in the face of contralateral ICA occlusion. Electroencephalography is a sensitive detector of cerebral ischemia and a valuable tool for determination of need for shunting during CEA. Surgeons should consider routine use of electroencephalography and selective shunting for significant electroencephalographic changes with clamping.

Preoperative MRA flow quantification in CEA patients: flow differences between patients who develop cerebral ischemia and patients who do not develop cerebral ischemia during cross-clamping of the carotid artery

BACKGROUND AND PURPOSE

We sought to investigate whether preoperative volume flow in the internal carotid arteries (ICAs), the basilar artery (BA), and the middle cerebral arteries (MCAs) and collateral flow via the circle of Willis differ between patients who do and patients who do not develop cerebral ischemia during clamping of the carotid artery in carotid endarterectomy (CEA).

METHODS

Quantitative volume flow in the ICAs, BA, and MCAs and directional flow in the circle of Willis were measured preoperatively with 2-dimensional phase-contrast MR angiography in 86 CEA patients. During the operation, electroencephalographic (EEG) recordings were obtained that were monitored by a clinical neurophysiologist. Reference volume flow values were assessed in 24 control subjects.

RESULTS

In patients with an ICA stenosis without contralateral ICA occlusion (n=62), of whom 16% developed ischemic EEG changes during clamping, preoperative flow in the clamped ICA was significantly higher in patients with cerebral ischemia than in patients without (mean, 278 versus 160 mL/min; P:<0.05). Flow in the contralateral ICA (156 versus 273 mL/min; P:<0.01), flow in the BA (116 versus 165 mL/min; P:<0.05), and presence of collateral flow via the circle of Willis to the clamped ICA (0% versus 37%; P:<0.05) were significantly lower. MCA flow did not differ significantly between groups. Additionally, in patients with an ICA stenosis and a contralateral ICA occlusion (n=24), of whom 42% developed cerebral ischemia, preoperative flow in the clamped ICA was significantly higher in patients with cerebral ischemia than in patients without (309 versus 239 mL/min; P:<0.05). BA flow, MCA flow, and presence of willisian collateral flow (0% versus 14%) did not differ significantly between groups.

CONCLUSIONS

Preoperative volume flow in the clamped ICA is significantly higher in CEA patients with ischemic EEG changes during clamping than in CEA patients without such changes. The latter patients probably have better developed collateral pathways preoperatively.

Computer-assisted EEG monitoring during carotid endarterectomy

The purpose of this study was to develop a reliable method of EEG analysis during carotid endarterectomy. EEGs of 104 patients under general anesthesia were processed by three different methods: a) "on-line" visual analysis during surgery, b) "off-line" visual analysis in laboratory, and c) computer analysis. To identify pathological EEGs, variability and asymmetry indexes of the 0.5-3.5 Hz and 8-15 Hz bands, absolute power and variability indexes of spectral edge frequency (SEF), and main dominant frequency were evaluated. On-line visual analysis showed clamp-related modifications in 29 EEGs (27.9%). Off-line visual analysis detected 24 pathological EEGs (23.1%): 18 with major changes and 6 with moderate changes. Computer analysis showed 21 EEGs (20.19%) with at least one altered index and 7 (6.7%) with altered variability for both SEF and 8-15 Hz power. The statistical analysis was significant for SEF variability and for 8-15 Hz power variability and asymmetry (P < 0.0001, analysis of variance test). While SEF and 8-15 Hz power variability did not appear influenced by anesthesia and single electrode artifacts, 8-15 Hz power asymmetry index was confounded by the presence of contralateral internal carotid occlusion. The data show that the use of these spectral indexes adds objective information to visual analysis, supporting and making easier intraoperative strategies. Their routine clinical use does not involve additional costs remaining technical requirements unchanged compared to traditional recording.

Influence of the status of the contralateral carotid artery on the outcome of carotid surgery

From 1985 to 1995, 747 carotid arteries were operated on in 694 patients, who were under general anesthesia and continuous electroencephalogram (EEG) monitoring. These patients were divided into three groups according to contralateral carotid status. Group 1 consisted of 58 patients who had contralateral occlusion; group 2, 53 patients who had contralateral stenosis and bilateral staged surgery; and group 3, 583 patients who had nonstenotic contralateral internal carotid artery. All groups were similar with regard to age and sex ratio. There were more asymptomatic patients in group 3 than in group 1 (39.9% vs. 25.8%) (p < 0.05), and less preoperative strokes in group 2 than in the other groups (3.7% vs. 17.2% and 13. 6%, respectively) (p < 0.05). Among risk factors, smoking was less frequent in group 3 (59.5%) than in group 1 (82.7%) and group 2 (77%) (p < 0.01), and coronary artery disease was more frequent in group 2 (60%) than in group 1 (32.7%) and Group 3 (26.4%) (p < 0.01). EEG changes occurred more frequently in group 1 (25.8%) than in group 2 [5.6% (first stage) and 3.8% (second stage)] and in group 3 (4.9%) (p < 0.01). A shunt was used only when EEG changes did not disappear after pharmacologic increasing of central blood pressure, which occurred more frequently in group 1 (10.3%) than in group 2 (0%) and group 3 (0.3%) (p < 0.05). The combined morbidity/mortality rate was similar for groups 1 and 3 (1.7% and 1.5%, respectively), however, transient morbidity was more frequent in group 1 (6.9%) than in group 3 (1.5%) (p < 0.05). The combined morbidity/mortality rate was higher in group 2 than in group 3 (7.5% vs. 1.5%) (p < 0. 05), and all strokes in group 2 were seen during the second-stage operation. In conclusion, contralateral carotid artery occlusion had minimal influence over carotid surgery results. Selective use of a shunt based on EEG monitoring prevented ischemic strokes, with minimal neurologic morbidity. Contralateral carotid stenosis did not affect operative strategy for first stage, but we noted a higher incidence of strokes during the second procedure.

Hemodynamic ischemic stroke during carotid endarterectomy: an appraisal of risk and cerebral protection

PURPOSE

The purpose of this study was to validate the commonly accepted indicators of risk of ischemic stroke that indicate the necessity for cerebral protection during carotid endarterectomy (CEA), and to examine the efficacy of high-dose thiopentone sodium (thiopental) as a cerebral protection method in patients who are at high risk of intraoperative ischemic stroke.

METHOD

In a prospective study of 37 CEAs performed for symptomatic stenosis > 70%, functional and clinical indicators of risk of ischemic stroke during carotid cross-clamping were identified. Functional indicators of risk were the development of ischemic electro-encephalogram (EEG) changes and stump pressure < 25 mm Hg. Clinical indicators of risk were previous ischemic hemispheric stroke and severe bilateral disease. These indicators were correlated in all patients, some of whom had two or three coexisting indicators of risk. The EEG and stump pressure were monitored continuously during carotid occlusion in all operations. Carotid occlusion times were recorded. Intraluminal shunting was eliminated in favor of high-dose thiopental cerebral protection in all patients. Neurologic outcome was deemed to measure the efficacy of thiopental protection in patients who are identified to be at risk and, hence, in need of cerebral protection. The validity of the indicators used to identify risk of ischemic stroke during CEA was assessed.

RESULTS

The absolute stroke risk was found to be 29.7% for the whole group (37 patients) and 57.9% in 19 patients who had commonly accepted indications for protective shunting. The correlation of ischemic EEG changes with stump pressure < 25 mm Hg was only 27.3%, whereas the expected correlation based on well-documented reports in the literature was 100%. The lack of correlation may have been related to the prevention of ischemic EEG changes by thiopental. There were no neurologic deficits in the series.

CONCLUSIONS

The absence of neurologic deficit in the study indicated that thiopental protection was effective in preventing ischemic stroke in high-risk patients and safely replaced intraluminal shunting.

Stump pressure, electroencephalographic changes, and the contralateral carotid artery: another look at selective shunting

BACKGROUND

Selective shunting during carotid endarterectomy is associated with the lowest operative stroke rate; therefore, patient selection for carotid shunting is critical. Electroencephalography (EEG) can detect ischemic brain cell dysfunction before irreversible injury. The carotid stump back pressure (CSP) has been inconsistent in determining the need for shunting, and contralateral carotid disease has had a variable impact. The purpose of this study was to evaluate CSP and operative EEG changes, and to determine the effect of contralateral carotid artery disease on determining the need for carotid shunting.

METHODS

In 140 consecutive carotid procedures, operative EEG and CSP were monitored, and contralateral carotid disease was documented. The carotid stump pressure/mean arterial pressure index (CSP/MAP) was also calculated to determine if this was a better indicator of the need for shunting than the CSP alone.

RESULTS

There was a 58% incidence of EEG changes when the CSP was < or = 25 mm Hg, 32% with a CSP of 26 to 50 mm Hg, and 4% with a CSP > 50 mm Hg. There was a 43% incidence of EEG changes and lower CSP among patients with a contralateral occlusion, both of which were significantly different from patients with a patent contralateral carotid artery. Three patients with CSP > 50 mm Hg had EEG changes, but none had a contralateral occlusion. Two patients had permanent neurologic deficits, and 2 had transient deficits. Excluding combined procedures, operative stroke rate was 0.8%.

CONCLUSIONS

A CSP of < 50 mm Hg achieved a sensitivity of 89% in patients who developed ischemic EEG changes during carotid clamping, and a pressure > 50 mm Hg had a negative predictive value of 96%. However, a CSP of < 50 mm Hg had a positive predictive value of only 36%. Neither the addition of the status of the contralateral carotid artery or the calculation of the CSP/MAP improved the sensitivity of the CSP in determining the need for shunting. Operative EEG monitoring remains the most sensitive guide to carotid shunting in patients undergoing carotid endarterectomy under general anesthesia.