Relation between middle cerebral artery blood flow velocity and stump pressure during carotid endarterectomy

Optimal cutoff value of carotid stump pressure for determining the need for a carotid shunt in carotid artery endarterectomy

OBJECTIVE

This study was conducted to identify the diagnostic value of carotid stump pressure for determining the need for a carotid artery shunt in patients undergoing carotid artery endarterectomy.

MATERIALS AND METHODS

Carotid stump pressure was prospectively measured in all carotid artery endarterectomies performed under local anesthesia between January 2020 and April 2022. The shunt was selectively used when neurological symptoms appeared after carotid cross-clamping. Carotid stump pressure was compared between patients who needed shunting and those who did not. Demographic and clinical characteristics, hematological and biochemical parameters, and carotid stump pressure of the patients with and without shunts were statistically compared. To determine the optimal cutoff value and diagnostic performance of carotid stump pressure for identifying the patients who need a shunt, receiver operating characteristic analysis was performed.

RESULTS

Overall, 102 patients (61 men and 41 women) who underwent carotid artery endarterectomy under local anesthesia were included, with an age range of 51-88 years. A carotid artery shunt was used in 16 (8 men and 8 women) patients. The carotid stump pressure values of the patients with a shunt were lower than those without a shunt (median (min-max): 42 (20-55) vs 51 (20-104), p < 0.0006). In the receiver operating characteristic curve analysis performed to determine the need for a shunt, the optimal cutoff value of carotid stump pressure was ≤48 mmHg, sensitivity was 93.8%, and specificity was 61.6% (area under the curve: 0.773, p < 0.0001).

CONCLUSION

Carotid stump pressure has sufficient diagnostic power to determine the need for a shunt, but it cannot be used alone in the clinical setting. Instead, it can be used in combination with other neurological monitoring methods.

ASNM and ASN joint guidelines for transcranial Doppler ultrasonic monitoring: An update

Today, it seems prudent to reconsider how ultrasound technology can be used for providing intraoperative neurophysiologic monitoring that will result in better patient outcomes and decreased length and cost of hospitalization. An extensive and rapidly growing literature suggests that the essential hemodynamic information provided by transcranial Doppler (TCD) ultrasonography neuromonitoring (TCDNM) would provide effective monitoring modality for improving outcomes after different types of vascular, neurosurgical, orthopedic, cardiovascular, and cardiothoracic surgeries and some endovascular interventional or diagnostic procedures, like cardiac catheterization or cerebral angiography. Understanding, avoiding, and preventing peri- or postoperative complications, including neurological deficits following abovementioned surgeries, endovascular intervention, or diagnostic procedures, represents an area of great public and economic benefit for society, especially considering the aging population. The American Society of Neurophysiologic Monitoring and American Society of Neuroimaging Guidelines Committees formed a joint task force and developed updated guidelines to assist in the use of TCDNM in the surgical and intensive care settings. Specifically, these guidelines define (1) the objectives of TCD monitoring; (2) the responsibilities and behaviors of the neurosonographer during monitoring; (3) instrumentation and acquisition parameters; (4) safety considerations; (5) contemporary rationale for TCDNM; (6) TCDNM perspectives; and (7) major recommendations.

Limitations of median nerve somatosensory evoked potential monitoring during carotid endarterectomy

OBJECTIVE

Hypoperfusion during carotid artery cross-clamping (CC) for carotid endarterectomy (CEA) may result in the major complication of perioperative stroke. Median nerve somatosensory evoked potential (MNSSEP) monitoring, which is an established method for the prediction of cerebral ischemia, has low sensitivity in detecting such hypoperfusion. In this study the authors sought to explore the limitations of MNSSEP monitoring compared to tibial nerve somatosensory evoked potential (TNSSEP) monitoring for the detection of CC-related hypoperfusion.

METHODS

The authors retrospectively analyzed data from patients who underwent unilateral CEA with routine shunt use. All patients underwent preoperative magnetic resonance angiography and were monitored for intraoperative cerebral ischemia by using MNSSEP, TNSSEP, and carotid stump pressure during CC. First, the frequency of MNSSEP and TNSSEP changes during CC were analyzed. Subsequently, variables related to stump pressure were determined by using linear analysis and those related to each of the somatosensory evoked potential (SSEP) changes were determined by using logistic regression analysis.

RESULTS

A total of 94 patients (mean age 74 years) were included in the study. TNSSEP identified a greater number of SSEP changes during CC than MNSSEP (20.2% vs 11.7%; p < 0.05). Linear regression analysis demonstrated that hypoplasia of the contralateral proximal segment of the anterior cerebral artery (A1 hypoplasia) (p < 0.01) and hypoplasia of the ipsilateral precommunicating segment of the posterior cerebral artery (P1 hypoplasia) (p = 0.02) independently and negatively correlated with stump pressure. Both contralateral A1 hypoplasia (OR 26.25, 95% CI 4.52-152.51) and ipsilateral P1 hypoplasia (OR 8.75, 95% CI 1.83-41.94) were independently related to the TNSSEP changes. However, only ipsilateral P1 hypoplasia (OR 8.76, 95% CI 1.61-47.67) was independently related to MNSSEP changes.

CONCLUSIONS

TNSSEP monitoring appears to be superior to MNSSEP in detecting CC-related hypoperfusion. Correlation with stump pressure and SSEP changes indicates that TNSSEP, and not MNSSEP monitoring, is a reliable indicator of cerebral ischemia in the territory of the anterior cerebral artery.

Assessment of boundary conditions for CFD simulation in human carotid artery

Computational fluid dynamics (CFD) is an increasingly used method for investigation of hemodynamic parameters and their alterations under pathological conditions, which are important indicators for diagnosis of cardiovascular disease. In hemodynamic simulation models, the employment of appropriate boundary conditions (BCs) determines the computational accuracy of the CFD simulation in comparison with pressure and velocity measurements. In this study, we have first assessed the influence of inlet boundary conditions on hemodynamic CFD simulations. We selected two typical patients suspected of carotid artery disease, with mild stenosis and severe stenosis. Both patients underwent digital subtraction angiography (DSA), magnetic resonance angiography, and the invasive pressure guide wire measured pressure profile. We have performed computational experiments to (1) study the hemodynamic simulation outcomes of distributions of wall shear stress, pressure, pressure gradient and (2) determine the differences in hemodynamic performances caused by inlet BCs derived from DSA and Womersley analytical solution. Our study has found that the difference is related to the severity of the stenosis; the greater the stenosis, the more the difference ensues. Further, in our study, the two typical subjects with invasively measured pressure profile and thirty subjects with ultrasound Doppler velocimeter (UDV) measurement served as the criteria to evaluate the hemodynamic outcomes of wall shear stress, pressure, pressure gradient and velocity due to different outlet BCs based on the Windkessel model, structured-tree model, and fully developed flow model. According to the pressure profiles, the fully developed model appeared to have more fluctuations compared with the other two models. The Windkessel model had more singularities before convergence. The three outlet BCs models also showed good correlation with the UDV measurement, while the Windkessel model appeared to be slightly better ([Formula: see text]). The structured-tree model was seen to have the best performance in terms of available computational cost and accuracy. The results of our numerical simulation and the good correlation with the computed pressure and velocity with their measurements have highlighted the effectiveness of CFD simulation in patient-specific human carotid artery with suspected stenosis.

Cerebral Neuromonitoring during Carotid Endarterectomy and Impact of Contralateral Internal Carotid Occlusion

BACKGROUND

The aim of this study was to identify the reliability of carotid artery stump pressure (SP) in predicting the neurologic changes and correlation with contralateral internal carotid artery (ICA) occlusion in patients undergoing eversion carotid endarterectomy (CEA). The optimal method for monitoring cerebral perfusion during CEA, performed under either local or general anesthesia, is still controversial.

METHODS

We prospectively analyzed 118 consecutive patients undergoing eversion CEA under local anesthesia. We had 78 symptomatic (66%) and 40 asymptomatic patients (33.9%). Selective shunting was performed in patients who developed neurologic changes after carotid clamping regardless of SP. Correlation of preoperative symptom status, a degree of stenosis, status of contralateral ICA, arterial blood pressure, SP value, and the intraoperative need for shunting due to neurologic changes was evaluated for both groups: shunted and nonshunted.

RESULTS

Selective shunting was performed in 12 patients (10%). There was no significant difference among the groups regarding the demographic characteristics. Mean carotid clamping time was 14.57 minutes. We had no perioperative mortality, stroke, or myocardial infarction. None of the patients required conversion to general anesthesia. We found a mean SP of 31 mm Hg as a reliable threshold for shunting (P < .001; sensitivity 92.3%; specificity 91.3%). Contralateral carotid occlusion was correlated with the significantly lower SP (27 ± 13 mm Hg; P = .001) and the higher need for shunt (50%).

CONCLUSIONS

SP measurement is a reliable and simple method for monitoring the collateral cerebral perfusion and can predict the need for shunting during CEA. Patients with the contralateral ICA occlusion showed significantly lower SP, although it did not have impact on the outcome.

Selective Carotid Shunting Based on Intraoperative Transcranial Doppler Imaging during Carotid Endarterectomy: A Retrospective Single-Center Review

Background

Carotid endarterectomy (CEA) with selective shunting is the surgical method currently used to treat patients with carotid artery disease. We evaluated the incidence of major postoperative complications in patients who underwent CEA with selective shunting under transcranial Doppler (TCD) at our institution.

Methods

The records of 45 patients who underwent CEA with TCD-based selective shunting under general anesthesia from November 2009 to June 2015 were reviewed. The risk factors for postoperative complications were analyzed using univariate and multivariate analysis.

Results

Preoperative atrial fibrillation was observed in three patients. Plaque ulceration was detected in 10 patients (22.2%) by preoperative computed tomography imaging. High-level stenosis was observed in 16 patients (35.5%), and 18 patients had contralateral stenosis. Twenty patients (44.4%) required shunt placement due to reduced TCD flow or a poor temporal window. The 30-day mortality rate was 2.2%. No cases of major stroke were observed in the 30 days after surgery, but four cases of minor stroke were noted. Univariate analysis showed that preoperative atrial fibrillation (odds ratio [OR], 40; p=0.018) and ex-smoker status (OR, 17.5; p=0.021) were statistically significant risk factors for a minor stroke in the 30-day postoperative period. Analogously, multivariate analysis also found that atrial fibrillation (p<0.001) and ex-smoker status (p=0.002) were significant risk factors for a minor stroke in the 30-day postoperative period. No variables were identified as risk factors for 30-day major stroke or death. No wound complications were found, although one (2.2%) of the patients suffered from a hypoglossal nerve injury.

Conclusion

TCD-based CEA is a safe and reliable method to treat patients with carotid artery disease. Preoperative atrial fibrillation and ex-smoker status were found to increase the postoperative risk of a small embolism leading to a minor neurologic deficit.

Preoperative beta blocker use associated with cerebral ischemia during carotid endarterectomy

PURPOSE

Cerebral ischemia is a known complication of carotid cross-clamping during carotid endarterectomy. Selective intraluminal shunting for cerebral protection is not always effective and carries risks. The purpose of this study was to identify potentially modifiable risk factors for intraoperative cerebral ischemia and shunting during carotid endarterectomy.

METHODS

We performed an historical case-control chart review of primary carotid endarterectomies with electroencephalographic (EEG) monitoring and selective shunting. Randomized controls and cases that showed ischemic EEG changes and required shunting were matched by year of surgery and the presence or absence of a contralateral carotid occlusion. Detailed perioperative data were collected for all cases. Results were analyzed using the Mantel-Haenszel test, analysis of variance, and a multivariate logistic regression model.

RESULTS

Of 523 charts screened, 69 patients had experienced evidence of cerebral ischemia on clamping of the carotid and required shunting. These patients were more likely than their matched controls to have been receiving regular preoperative beta blockers (33/69 vs 18/69, respectively; P = 0.01; odds ratio [OR] 2.5; 95% confidence interval [CI] 1.2 to 5.1). Ipsilateral moderate carotid stenosis (60-80%) was also associated with increased risk. An adjusted multivariate regression model estimated an OR of 3.6 (95% CI 1.5 to 8.9; P = 0.005) for the association between use of a beta blocker and shunting. Intraoperative hemodynamic values were similar for the shunt and control groups as well as for patients receiving and not receiving preoperative beta blockers.

CONCLUSION

The current study found an association between regular preoperative use of beta blockers and intraoperative cerebral ischemia in patients undergoing carotid endarterectomy. This effect did not relate to intraoperative hemodynamics.

Intracranial collateralization determines hemodynamic forces for carotid plaque disruption

INTRODUCTION

Percent diameter reduction provides an imperfect assessment of the risk for stroke from carotid atheroembolism. Stroke associated with atherosclerotic carotid stenosis commonly results from plaque disruption brought about by hemodynamic shear stress and Bernoulli forces. The aim of the present study was to predict the effect of incomplete intracranial collateralization through the circle of Willis (COW) on disruptive hemodynamic forces acting on carotid plaques.

METHODS

A simple circuit model of the major pathways and collaterals that form and supply the COW was developed. We modeled the intra- and extracranial arterial circuits from standard anatomic references, and the pressure-flow relationships within these conduits from standard fluid mechanics. The pressure drop caused by (laminar and turbulent) flow along the internal carotid artery path was then computed. Carotid circulation to the brain was classified as being with or without collateral connections through the COW, and the extracranial carotid circuit as being with or without severe stenosis. The pressure drop was computed for each scenario. Finally, a linear circuit model was used to compute brain blood flow in the presence/absence of a disconnected COW.

RESULTS

Pressure drop across a carotid artery stenosis increased as the flow rate within the carotid conduit increased. Poststenotic turbulence from a sudden expansion distal to the stenosis resulted in an additional pressure drop. Despite the stenosis, mean brain blood flow was sustained at 4.15 mL/s bilaterally. In the presence of an intact (collateralized) COW, this was achieved by enhanced flow in the contralateral (normal) carotid artery. However, in a disconnected COW, this was achieved by sustained systolic and enhanced diastolic flow through the stenosed artery. For a similar degree of stenosis, flow and velocity across the plaque was much higher when the COW was disconnected compared with an intact COW. Furthermore, the pressure drop across a similar stenosis was significantly higher with a disconnected COW compared with an intact COW.

CONCLUSIONS

Incomplete intracranial collateralization through the COW results in increased flow rates and velocities, and therefore large pressure drops across a carotid artery stenosis. This exerts large disruptive shear stress on the plaque compared with patients with an intact COW. Percent diameter reduction provides an inaccurate assessment of risk for atheroembolic stroke. An assessment of carotid flow rates, flow velocities, and the intracranial collateral circulation may add independent information to refine the estimation of stroke risk in patients with asymptomatic carotid atherosclerosis.

Correlation of intraoperative collateral perfusion pressure during carotid endarterectomy and status of the contralateral carotid artery and collateral cerebral blood flow

BACKGROUND

The optimal method for predicting when carotid shunting is not necessary during carotid endarterectomy (CEA) is controversial. This study will analyze the correlation of collateral perfusion pressure and the status of contralateral carotid/cerebral collaterals and determine whether preoperative duplex ultrasound/cerebral angiography can predict when CEA can be done without shunting.

METHODS

Ninety-eight patients were randomized into routine shunting and 102 into selective shunting when the collateral perfusion pressure (systolic carotid stump pressure) was <40 mm Hg during CEA. All patients had preoperative carotid duplex ultrasound and 87 had angiography, the results of which were evaluated for the presence of collateral flow from the contralateral carotid artery or posterior circulation through the anterior and/or posterior communicating arteries.

RESULTS

The perioperative stroke rate was 1.5% for the entire group. There was no correlation between preoperative symptoms and the status of the contralateral carotid artery (normal, stenosed, or occluded). The mean collateral perfusion pressure was inversely related to the severity of the contralateral carotid stenosis: 60, 57, 55, 56, and 38 mm Hg for normal, <50% stenosed, 50-69% stenosed, 70-99% stenosed, and occluded arteries, respectively (p = 0.005). There was a direct relation between the number of patients with a collateral perfusion pressure of <40 mm Hg (shunted group) and the severity of the contralateral carotid stenosis: 6 of 62 (10%) for normal carotid, 7 of 43 (16%) for <50% stenosis (OR = 1.82), 12 of 69 (17%) for 50-69% stenosis (OR = 1.97), 3 of 10 (30%) for 70-99% stenosis (OR = 4, CI = 0.81-19.68), and 9 of 13 (70%) for occlusion (OR = 21, CI = 4.98-89.32) (p < 0.0001). None of the patients (0/56) with normal to <70% contralateral carotid stenosis with cross-filling had a collateral perfusion pressure of <40 mm Hg (no shunting was necessary). However, 9 of 17 (47%) patients with <70% contralateral carotid stenosis and no cross-filling had a collateral perfusion pressure of <40 mm Hg (p < 0.0001), whereas 6 of 7 (86%) patients with ≥70% contralateral carotid stenosis and cross-filling versus 2 of 7 (29%) with ≥70% contralateral carotid stenosis and no cross-filling had a collateral perfusion stump pressure of >40 mm Hg (p = 0.1026). Overall, 62 of 63 (98.4%) patients with cross-filling versus 10 of 24 (42%) without cross-filling had a collateral perfusion pressure of ≥40 mm Hg (p < 0.0001).

CONCLUSIONS

There was an inverse correlation between collateral perfusion pressure and severity of contralateral carotid stenosis, and patients with severe contralateral carotid stenosis/occlusion were more likely to be shunted. The presence of cross-filling with normal to <70% contralateral carotid stenosis was associated with a collateral perfusion stump pressure of ≥40 mm Hg in 100% of patients for whom shunting was not carried out in our series.

Effectiveness of near-infrared spectroscopy during surgical repair of tracheo-innominate artery fistula

Monitoring regional cerebral oxygen saturation (rSO(2)) by use of near-infrared spectroscopy (NIRS) is a useful method for detecting cerebral ischemia. Tracheo-innominate artery fistula is a rare but life-threatening complication of tracheostomy. The surgical procedures for management of tracheo-innominate artery fistula include direct or patch closure of the fistula, ligation or division of the innominate artery, and anatomical or extra-anatomical reconstruction of the flow of the innominate artery. Division of the innominate artery is the best method to prevent postoperative recurrence of bleeding and infection. However, cutting off the innominate artery flow may cause brain ischemia. We present the case of a patient with tracheo-innominate artery fistula successfully treated by dividing the innominate artery while the rSO(2) was monitored. In this case report, we have shown that NIRS is a useful method for deciding the surgical maneuver for tracheo-innominate artery fistula.

Prospective randomized trial of routine versus selective shunting in carotid endarterectomy based on stump pressure

BACKGROUND

The use of shunting in carotid endarterectomy (CEA) is controversial. This randomized trial compared the results of routine (RS) vs selective shunting (SS) based on stump pressure (SP).

METHODS

Two-hundred CEA patients under general anesthesia were randomized into RS (98 patients) or SS (102 patients), where shunting was used only if systolic SP (SSP) was <40 mm Hg. Clinical and demographic characteristics were comparable in both groups. Patients underwent immediate and 30-day postoperative duplex ultrasound follow-up. Analysis was by intention-to-treat.

RESULTS

Of 102 SS patients, 29 (28%) received shunting. Indications for CEA were similar (42% symptomatic for RS; 47% for SS, P = .458). The mean internal carotid artery diameter was comparable (5.5 vs 5.5 mm, P = .685). Mean preoperative ipsilateral and contralateral stenosis was 76% and 38% for RS (P = .268) vs 78% and 40% for SS (P = .528). Mean preoperative ipsilateral and contralateral stenosis was 79% and 56% in the shunted (P = .634) vs 78% and 34% in the nonshunted subgroup of SS patients (P = .002). The mean SSP was 55.9 mm Hg in RS vs 56.2 for SS (P = .915). The mean SSP was 33 mm Hg in the shunted vs 65 in the nonshunted subgroup (P < .0001). Mean clamp time in the nonshunted subgroup of SS was 32 minutes. Mean shunt time was 35 minutes in RS and 33 in SS (P = .354). Mean operative time was 113 minutes for RS and 109 for SS (P = .252), and 111 minutes in shunted and 108 in the nonshunted subgroup (P = .586). Mean arteriotomy length was 4.4 cm for RS and 4.2 for SS (P = .213). Perioperative stroke rate was 0% for RS vs 2% for SS (one major and one minor stroke, both related to carotid thrombosis; P = .498). No patients died perioperatively. Combined perioperative transient ischemic attack (TIA) and stroke rates were 2% in RS vs 2.9% in SS (P > .99). The overall perioperative complication rates were 8.3% in RS (2 TIA, 3 hemorrhage, 1 myocardial infarction [MI], and 1 asymptomatic carotid thrombosis) vs 7.8% in SS (2 strokes, 1 TIA, 3 hemorrhage, 1 MI, and 1 congestive heart failure; P = .917).

CONCLUSIONS

RS and SS were associated with a low stroke rate. Both methods are acceptable, and surgeons should select the method with which they are more comfortable.

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.

Prevention of Ischemic Neurologic Injury With Intraoperative Monitoring of Selected Cardiovascular and Cerebrovascular Procedures: Roles of Electroencephalography, Somatosensory Evoked Potentials, Transcranial Doppler, and Near-Infrared Spectroscopy

All neuromonitoring techniques, although imperfect, provide useful information for monitoring cardiothoracic and carotid vascular operations. They may be viewed as providing complementary information, which may help surgical technique and, as a result, possibly improve clinical outcomes. As of this writing, the efficacy of TCD and NIRS monitoring during cardiothoracic and vascular surgery cannot be considered established. Well designed, prospective, adequately powered, double-blind, and randomized outcome studies are needed to determine the optimal neurologic monitoring modality (or modalities), in specific surgical settings.

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.

Unruptured large intracranial aneurysms in patients with transient cerebral ischemic episodes

This report analyzes the treatment of six patients with transient cerebral ischemic episodes in combination with large unruptured aneurysm. Priority treatment of the symptomatic lesions had to be delayed in five cases because the large aneurysms were ipsilateral to stenoses of the internal carotid artery. The hemodynamic effect of surgery on the compromised cerebral circulation was pre-examined with digital subtraction angiography and technetium-99m ((99m)Tc) single photon emission computed tomography. The data were correlated to aneurysm location and anatomical territory of the transient ischemic episodes. Only one patient showing a severe carotid stenosis contralateral to the large aneurysm, with decreased technetium uptake in the symptomatic hemisphere, required surgical correction of the stenosis first. In five patients, areas of reduced (99m)Tc uptake were mostly found within vascular boundary zones with angiographically verified effective collateral circulation. Clipping of the large aneurysms in these patients ipsilaterally to the stenotic lesion or on the anterior communicating artery as first option did not substantially increase the risk of subsequent stroke.

Cerebral hemodynamics immediately following carotid occlusion

During carotid endarterectomy, we routinely monitor internal carotid artery pressure (P(ICA)) and middle cerebral artery flow velocity (V(MCA)). P(ICA) has been previously shown to accurately reflect pressure at the origin of the middle cerebral artery, even during times of rapidly changing pressure such as occurs with sudden occlusion of the common carotid artery. We retrospectively analyzed pressure recordings around the time of carotid cross clamping in 29 consecutive carotid endarterectomy operations. Suitable transcranial Doppler recordings of V(MCA) were available from eight of the operations. Comparing the cardiac cycle prior to cross clamping with the first complete cardiac cycle after cross clamping, the mean P(ICA) fell from 93 mm Hg to 62 mm Hg and the mean V(MCA) fell from 41 cm x sec-1 to 25 cm x sec-1. Over the subsequent 10 seconds, there was a further decrease in P(ICA) to 51 mm Hg (P <.0001), while V(MCA) changed in the opposite direction, increasing to 32 cm x sec-1 (P <.01). The patients with the greatest decrease in P(ICA) immediately on cross clamping also had the greatest additional decrease over the following 10 seconds (r = 0.74). The increase in V(MCA) during the first 10 seconds after carotid occlusion is well recognized and is presumed to be due to autoregulatory vasodilatation. The simultaneous decrease that we observed in P(ICA) indicates an increase in the pressure gradient along the collateral vessels, which is to be expected during a period of increasing flow along those vessels.

Unruptured intracranial aneurysms in patients with transient cerebral ischemic episodes. Optional managements and literature review

Clinical experience about the management of patients with an unruptured intracranial aneurysm (UIA) presenting transient cerebral ischemic attacks (TIAs) is usually restricted to a few case reports. Some authors assume tha it is safe to perform an endarterectomy without acutely increasing the risk of aneurysm rupture while others reported a post-operative aneurysmal bleeding even for aneurysms smaller than 10 mm between some days and several months after endarterectomy. The aim of this paper is to analyse the factors involved in the particular ischemic episodes, the examination methods to be employed, and the optional management for each individual case on a literature review and own experience-based data.

Remifentanil conscious sedation during regional anaesthesia for carotid endarterectomy: rationale and safety

OBJECTIVES

to prospectively evaluate the safety and efficacy of remifentanil during regional anaesthesia for carotid endarterectomy.

METHODS

twenty-eight consecutive patients underwent carotid endarterectomy with combined superficial and deep cervical plexus block supplemented with continuous intravenous 0.04 microg.kg(-1).min(-1)remifentanil infusion. Depth of sedation was monitored using the Observer's Assessment of Alertness/Sedation Scale (OAA/S). The degree of pain, discomfort and anxiety was self-assessed by the patients using a horizontal visual analogue scale.

RESULTS

all patients experienced adequate comfort and analgesia. No local anaesthetic supplementation was necessary. No patient had a OAA/S score lower than 4 (with 5=awake/alert to 1=asleep). Respiratory depression did not occur. Selective shunting was required in four cases. No patient was converted to general anaesthesia. There were no permanent neurological deficits, cardiopulmonary complications or deaths.

CONCLUSION

remifentanil as a supplement to regional anaesthesia for carotid endarterectomy, provides comfort and analgesia without hampering mental status evaluation.

Transcranial Doppler ultrasonography: year 2000 update

In this update, the main clinical applications of transcranial Doppler ultrasonography are reassessed. A specific format for technology assessment, personal experience, and an extensive review of the literature form the basis of the evaluation. The document is approved by the American Society of Neuroimaging and the Neurosonology Research Group of the World Federation of Neurology.

Transcranial Doppler findings during balloon test occlusion of the internal carotid artery

The authors performed transcranial Doppler ultrasonography (TCD) during internal carotid artery (ICA) balloon test occlusion (BTO) and observed changes in mean flow velocity (Vm) in the middle cerebral artery (MCA), and pulsatility index (PI) while monitoring the stump pressure (Sp) of the internal carotid artery (ICA), and neurologic findings. A group of 17 patients requiring possible temporary or permanent occlusion of the ICA in the course of planned procedures first underwent BTO. A patient who either developed neurologic changes or maintained less than 60% of preocclusion Sp or Vm in the ipsilateral MCA during BTO was considered to have a positive test. Eleven patients had negative results, while in six patients, tests were positive. Mean flow velocity showed a decrease after occlusion in all cases but not to a remarkable extent in some patients. Stump pressure decreased in all negative cases after balloon inflation and than tended to increase progressively during 15 minutes of BTO. Pulsatility index tended to decrease gradually during BTO in all negative patients. However, in positive cases, PI and Sp fell steeply. Only one positive case had a neurologic symptom of severe headache. The decreased PI in the MCA reflected autoregulatory dilation of cerebral vessels to compensate for decreased absolute cerebral blood volume following ICA occlusion. Changes in PI are a good indicator for evaluating blood flow during BTO.

Hemodynamic evaluation by using near infrared spectroscopy during carotid endarterectomy

To evaluate the hemodynamic changes during carotid endarterectomy, we compared changes in oxyhemoglobin levels with changes in the internal carotid artery flow and the somatosensory evoked potential (SEP). In 40 of 42 patients, the oxyhemoglobin level, measured in the frontal area on the operated side using near infrared spectroscopy (NIRS), decreased immediately after cross-clamping the internal carotid artery and returned to the preclamping level after the clamp was removed. There was no linear relationship between the internal carotid flow and the decrement in the oxyhemoglobin level after carotid clamping. Nineteen patients (45%) had a large internal carotid flow (> or =90 mL/min), but a small decrease in the oxyhemoglobin level (<0.04 in index); presumably these patients had adequate collateral circulation. Eight patients (19%) had a large internal carotid flow and a marked decrease in the oxyhemoglobin level (> or =0.04); presumably these patients had insufficient collateral circulation. The changes in oxyhemoglobin and SEP after carotid clamping agreed in 77.5% of the patients; however, in the other 22.5%, the disparity between the two factors indicated different causes of cerebral ischemia following carotid clamping. A marked decrease in oxyhemoglobin without a significant change in SEP suggests ischemia predominantly in the frontal area, whereas a small decrease in oxyhemoglobin and a significant change in SEP suggest ischemia predominantly in the somatosensory pathway or cortex. In conclusion, the relationship between the internal carotid flow and the change in HbO(2) provides information about the collateral circulation. Simultaneous monitoring of NIRS and SEP is useful for assessing of the pattern of cerebral ischemia during carotid clamping.

Transcranial Doppler ultrasonography-guided management of internal carotid artery closure

OBJECTIVE

To emphasize the integrated use of transcranial Doppler ultrasonography (TCD) in the management of internal carotid artery (ICA) closure.

METHODS

Thirty-three patients being considered for ICA closure underwent TCD assessment, vasomotor reserve testing/estimation, and carotid artery test occlusion with concomitant middle cerebral artery (MCA) blood velocity (V(MCA)) monitoring, including calculation of the MCA pulsatility index. Twelve of these patients proceeded to undergo ICA sacrifice. Sequential TCD sonograms guided their postoperative treatment.

RESULTS

ICA aneurysms and neck neoplasms affected the TCD results and vasomotor reserve insignificantly, whereas carotid-cavernous fistulae induced characteristic circulatory alterations. The 10 subjects who tolerated ICA sacrifice hemodynamically all showed an initial decrease in the ipsilateral V(MCA) to > or =60% of the preocclusion value and a progressively decreasing MCA pulsatility index during carotid artery test occlusion. The two patients who developed hemodynamic cerebral infarctions exhibited a decrease in V(MCA) to <60% and a MCA pulsatility index that remained stable after a vast initial reduction. Postoperative hypervolemic and hypertensive support was safely titrated in all patients who received postoperative TCD surveillance, providing an ipsilateral V(MCA) of > or =80% of the preocclusion value. ICA closure permanently altered the cerebral circulatory pattern.

CONCLUSION

The hemodynamic outcome of ICA sacrifice can be correctly predicted by using the TCD occlusion test. TCD provides the means to titrate the extent of postoperative hypervolemic/hypertensive support.

Intracarotid pressure measurements in the evaluation of a computer model of the cerebral circulation

BACKGROUND

It is difficult to predict which patients will tolerate occlusion of the internal carotid artery. This difficulty arises primarily because of uncertainties in the prediction of the adequacy of collateral circulation. Because of these uncertainties, balloon test occlusion and other methods have been developed to determine a priori the safety of carotid occlusion. However, all the methods are associated with significant false-positive and false-negative rates, as well as other neurologic complications. Because of these problems, more accurate and less invasive methods for predicting tolerance of carotid occlusion are needed.

METHODS

In this report, we present the initial clinical evaluation of a new method for assessing the collateral circulation aided by a mathematical model of the cerebral vasculature. Data from the angiograms of 14 patients who underwent carotid endarterectomy were used to create individualized simulations of their cerebral circulations. As a test of the accuracy of the simulations, we compared values of the intracarotid stump pressures predicted by the model to those measured at surgery during the period of carotid occlusion.

RESULTS

The pressure predictions of the model correlated well with those measured at surgery. Linear regression analysis of measured versus predicted values yielded a line with slope 1.05. The line with slope 1.00, which denotes perfect agreement between predictions and measurements, is within the 95% confidence interval of the slope determined from the regression analysis.

CONCLUSIONS

Mathematical models of the cerebrovascular circulation can provide good predictions of intravascular pressure in the collateral circulation, and may provide accurate predictions of the flow as well. The present study reveals several areas that need further development, such as the models of the microvasculature, measurement of the arterial dimensions from angiograms, and consideration of other collateral sources such as the leptomeningeal and retrograde ophthalmic sources of flow. Incorporation of these improvements may lead to a clinically useful, noninvasive assessment of the state of the cerebrovascular collateral circulation in the individual patient.

Microembolic signals and intraoperative stroke in carotid endarterectomy

OBJECTIVES

Microembolic signals (high-intensity transient signals, HITS) detected by means of transcranial Doppler sonography (TCD) may be relevant for intraoperative strokes in carotid endarterectomy (CEA).

MATERIAL AND METHODS

An intraoperative HITS detection study was performed on 77 patients (63 men, 14 women, mean age+/-SD, 64+/-8 years) with a total of 81 CEAs. Using the Scandinavian Stroke Scale the patients were clinically examined by a neurologist preoperatively and postoperatively within 6 h. A deterioration of the Scandinavian Stroke Scale was considered an intraoperative stroke if persisting longer than 24 h. Cranial computed tomography (CT scan) was performed preoperatively and 3 to 5 days postoperatively. By means of TCD total HITS count and mean blood velocity changes, for shunting, were recorded sufficiently in the middle cerebral artery in 79 CEAs.

RESULTS

HITS were significantly more frequent in symptomatic [n = 53; HITS: median, 15 (range 1-159)] than in asymptomatic stenoses [n = 26; HITS: 6.5 (0-41); P < 0.001]. An intraoperative stroke in the hemisphere ipsilateral to the operation occurred in eight of the 81 CEAs. On postoperative CT scans, five of the eight strokes showed new corresponding territorial infarctions. In the three strokes without new CT lesions, the mean blood velocity changes after clamping indicated normal cerebral perfusion. Total HITS count was significantly higher in procedures with intraoperative strokes [n = 8; HITS: 33 (11-159)] than in the uncomplicated [n = 71; HITS: 10 (0-62); P = 0.002]. No stroke occurred in 37 CEAs with 10 or less HITS, but eight in 42 CEAs with 11 or more HITS [P = 0.006; relative risk 1.23 (95% confidence interval: 1.06 to 1.43)].

CONCLUSION

Microembolism seems clinically relevant in carotid endarterectomy. Asymptomatic patients may run a lower risk of intraoperative embolization.

Cerebral haemodynamics in internal carotid artery trial occlusion

The purpose of this study was to analyse the cerebral haemodynamic changes brought about by trial occlusion of the internal carotid artery (ICA). Sixteen patients with surgically inaccessible cerebral aneurysms, carotid cavernous fistulas or neck neoplasms were monitored with transcranial Doppler ultrasonography (TCD) during 90-120 s angiographic ICA balloon occlusion or ICA closure with a Selverstone clamp. The blood velocity (V) was registered continuously in both middle cerebral arteries (MCA) while the pulsatility index (PIMCA) and haemodynamic tension (Uhem MCA) were calculated. ICA closure led to an instantaneous drop in the ipsilateral VMCA, PIMCA and Uhem MCA. The VMCA thereafter increased gradually until reaching a stable level. The subjects were grouped into those with initial drops in VMCA to > or = 60% of pre-occlusion value (group 1) and those that fell to < 60% (group 2), respectively. In group 1 autoregulatory mechanisms made the PIMCA decline further, while the Uhem MCA remained unaltered during ICA closure. In group 2, however, the PIMCA did not change further, while the Uhem MCA increased slightly. The cerebral haemodynamic features during ICA test occlusion were thus essentially different in the two groups. On re-opening the ICA, there was an overshoot in VMCA and Uhem MCA. Contralaterally, the VMCA was increased during ICA occlusion. Seven of the patients later had their ICA closed permanently. While none of five group 1 patients developed haemodynamic complications, two group 2 individuals experienced haemodynamic stroke. Assuming ICA sacrifice is feasible when test occlusion results in an ipsilateral initial reduction in VMCA to > or = 60% of pre-occlusion value, the corresponding limit for the Uhem MCA is > or = 40%. In the pre-operative evaluation of the haemodynamic risk related to ICA loss, TCD emerges as a reliable method. It also seems to allow for the reduction of test occlusion time to 90-120 s.

Transcranial Doppler monitoring during carotid endarterectomy: is it appropriate for selecting patients in need of a shunt?

PURPOSE

This report summarizes our experience in evaluating a series of 168 patients who underwent a total of 175 carotid endarterectomy procedures under local anesthesia. Patients were monitored by stump pressure (SP) measurement and transcranial Doppler scanning (TCD). The need for shunting was compared between SP/TCD flow velocity reduction and the awake response (gold standard).

METHODS

The study cohort represented 56% of all the carotid patients treated during the study period. Clamping ischemia was defined as the appearance of focal deficit (focal ischemia) or unconsciousness (global deficit) on carotid clamping. In the case of clamping ischemia, a shunt was inserted. To define the optimal value of SP and TCD flow velocity that is able to discriminate patients with clamping ischemia, a receiver operator characteristic (ROC) curve was constructed. Sensitivity and specificity tests, together with negative and positive predictive values (NPV and PPV), were calculated. Cutoff values were defined as the ROC curve values that correlated the highest sensitivity with the highest specificity for both SP and TCD.

RESULTS

Clamping ischemia was present in 18 procedures (10%) in which a shunt was used. No perioperative deaths were recorded. Major perioperative morbidity occurred in one patient (0.6%). Two nondisabling strokes were also recorded (1.8% overall rate of neurologic morbidity). Cutoff values for both SP and TCD, using the ROC curve, were < or = 50 mm Hg and > or = 70% flow velocity reduction from baseline, respectively. SP values of < or = 50 mm Hg or less showed a sensitivity of 100%, a specificity of 83%, a PPV of 40%, and an NPV of 100%. TCD flow monitoring (> or = 70% flow reduction) revealed a lower sensitivity (83%) but a greater ability to avoid false positive results (96% specificity), resulting in increased PPV (71%) and NPV (98%). Combining SP and TCD failed to provide better results in terms of specificity (81%) and PPV (38%).

CONCLUSIONS

SP measurement using a 50 mm Hg cutoff appears to be a reliable predictor of clamping ischemia but requires the use of a shunt in 17% of the patients who would otherwise not require this procedure. In contrast, TCD has greater specificity but is associated with a lower sensitivity, with 17% false negative results. In our experience, both SP and TCD show limitations, as they overestimate or underestimate carotid endarterectomy procedures in need of a shunt. We believe that sensitivity is more important than specificity in carotid endarterectomy, and thus conclude that TCD flow velocity measurement is not an optimal method for detecting clamping ischemia.

Transcranial Doppler monitoring and causes of stroke from carotid endarterectomy

BACKGROUND AND PURPOSE

The value of carotid endarterectomy (CEA) depends on the safety of the operation. Transcranial Doppler ultrasound (TCD) was used to evaluate the possibilities of hypoperfusion, hyperperfusion, and embolization as causes of stroke and to evaluate the significance of Doppler microembolic signals (DMES).

METHODS

Five hundred CEAs were monitored with TCD of the ipsilateral middle cerebral artery during various phases of CEA to determine hemodynamic changes and incidence of DMES. Complications were graded according to their severity, and their probable cause was determined from TCD criteria and review of hospital charts.

RESULTS

We observed 24 cerebrovascular complications (4.8%), including 9 with transient ischemic attacks and 15 (3%) with permanent deficits. Among all cerebrovascular complications, embolism was judged to be responsible in 13 (54%; P < .02 compared with hypoperfusion), hyperperfusion in 7 (29%; P < .14 compared with hypoperfusion), and hypoperfusion in 4 (17%; P < .08 compared with embolism plus hyperperfusion). The surgeons responded to TCD information by several strategies depending on the TCD information. The incidence of permanent deficits diminished from 7% in the first 100 operations to 2% in the last 400 (P < or = .01). Shunting was more strongly associated with cerebrovascular complications than nonshunting, but this difference was not significant (P = .24). Intraoperative prevalence of DMES was strongly associated with cerebrovascular complications (P = .02).

CONCLUSIONS

Embolism is the principal cause of cerebrovascular complications from CEA; hyperperfusion and hypoperfusion are also important causes. TCD provides information that allows prompt identification and treatment of these three major causes of stroke from this operation. The perioperative stroke rate can be reduced by appropriate measures, taken by the surgeons, based on findings of TCD monitoring.

Transcranial Doppler intraoperative monitoring during carotid endarterectomy: experience with regional or general anesthesia, with and without shunting

To determine whether continuous transcranial Doppler (TCD) can significantly alter therapeutic conduct during carotid endarterectomy, a retrospective study of 117 carotid endarterectomies was done. There was no perioperative mortality; one perioperative stroke was recorded in a patient who was symptomatic preoperatively. Continuous TCD of the ipsilateral middle cerebral artery (MCA) was attempted in 99 cases, and successful in 90; nine patients (9.1%) had inadequate temporal windows for MCA access. MCA velocities and emboli were recorded before and during carotid cross-clamping, and on clamp release. There were no significant velocity differences between the patients with regional and general anesthesia, and patients with and without carotid shunts, but there was a statistically significant difference in the total number of emboli (air and particulate transients) noted for the shunted and nonshunted patients after clamp release: 12.7 versus 23.6, respectively (p = 0.05). There was no significant difference when particulate and air microemboli were compared. During surgery TCD identified residual flow of less than 40% in the MCA in 17 patients (18.8%). TCD also identified hyperperfusion in two patients, shunt abnormalities in three patients, and influenced postop treatment in four patients, one of whom was returned to surgery. TCD is an important tool for identifying patients who would benefit from a shunt, preventing hyperperfusion, identifying postop emboli, and detecting technical errors.

Is transcranial Doppler effective in avoiding the hazards of carotid surgery?

The middle cerebral artery flow velocities were measured to test the hypothesis that transcranial Doppler is a useful technique for intraoperative monitoring in 50 consecutive carotid endarterectomies which were performed under local anaesthesia. The patients' neurological status was continuously monitored. The peak middle cerebral artery velocities were measured before clamping, during clamping and after restoration of flow, and again 24 h and 4 weeks later. Clamping produced a decrease in the velocity of the middle cerebral artery, from 97 to 45 cm/s (P < 0.001). Neurological manifestations occurred in eight patients; one patient lost consciousness, and seven experienced transient focal deficits during the procedure. Another three (6%) developed minor strokes postoperatively. The velocity changes were similar in those who developed complications to those who did not. These results do not support the view that transcranial Doppler monitoring is helpful in deciding whether to use a shunt during carotid endarterectomy. Further data are needed to evaluate the importance of transcranial Doppler monitoring during carotid surgery.

The relationship between cerebral blood flow and transcranial Doppler blood flow velocity during hypothermic cardiopulmonary bypass in adults

A noninvasive, simple, and continuous method to assess cerebral perfusion during cardiopulmonary bypass (CPB) could help prevent cerebral ischemia. Transcranial Doppler sonography (TCD) allows a noninvasive, on-line measurement of blood flow velocity in cerebral arteries. The correlation of TCD-estimated and actual cerebral blood flow (CBF) has not been well studied during CPB. We determined the correlation of middle cerebral artery (MCA) mean velocity and CBF determined by the Kety-Schmidt method during nonbypass and two hypothermic bypass flow conditions. Sixteen patients undergoing hypothermic (27 degrees C) CPB for coronary artery bypass grafting and/or valve replacement surgery were enrolled in the study. We were able to determine MCA velocity in only 12 patients. We determined CBF and MCA velocity in each patient during four 15-min study periods: 1) prebypass after sternotomy before aortic cannulation; 2) hypothermic (27 degrees C) CPB with 1.2 L.min-1.m-2 pump flow; 3) hypothermic CPB with 2.4 L.min-1.m-2 pump flow, and 4) 30 min after weaning from CPB. There was no difference in the mean arterial pressure between the two CPB pump blood flows. The pooled change in MCA velocity and CBF as percentage of baseline (prebypass) for all patients and at all time points had a correlation of 0.33 (r). A decrease or increase in MCA velocity did not necessarily indicate a corresponding decrease or increase in CBF. This technology may be of limited usefulness during the circulatory condition of hypothermic, nonpulsatile CPB.

Near-infrared monitoring of cerebral oxygenation state during carotid endarterectomy

BACKGROUND

Recent studies have indicated that near-infrared spectroscopy (NIRS) could continuously and noninvasively observe the changes in cerebral oxygenation state during hypoxia and ischemia, using their optical properties. Its validity and usefulness during cerebrovascular surgery, however, still remain to be clarified.

METHODS

Using NIRS, we continuously monitored the changes in the concentration of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin ([oxy-HB], [deoxy-Hb], and [total Hb], respectively) and redox state of cytochrome oxidase (cyt ox) during carotid endarterectomy for 22 patients, and we compared the NIRS responses with those of intraoperative somatosensory evoked potentials (SEP) and regional cerebral blood flow (rCBF).

RESULTS

In 9 of 22 patients, cross-clamping of the carotid artery caused a continuous decrease [oxy-Hb] and [total Hb], and an increase in [deoxy-Hb]. Cyt ox was partially reduced during the clamping. These NIRS responses demonstrated the occurrence of severe hypoxia in the ipsilateral cerebral tissue. These patients showed a marked decrease in the N20 amplitude of SEP and rCBF. In contrast, the other 13 patients did not show a significant decrease in the cerebral oxygenation state, which showed no remarkable changes in either SEP or in rCBF.

CONCLUSIONS

NIRS could successfully jude the cerebral oxygenation state noninvasively during carotid surgery and was more sensitive to ischemic crisis than other indirect methods.

A comparison of quality control methods applied to carotid endarterectomy

OBJECTIVES

To compare the ability of continuous wave Doppler (CWD), B-mode ultrasound (BMU), angioscopy and transcranial Doppler (TCD) to detect technical error during carotid endarterectomy (CEA).

DESIGN

A prospective, comparative study in 100 consecutive patients.

SETTING

Leicester Royal Infirmary, Leicester, U.K.

MATERIALS

Intraoperative TCD monitoring was performed using a SciMed PcDop 842 2 MHz TCD. An Olympus 2.8mm flexible angioscope was used to inspect the arterial lumen prior to restoration of bloodflow. After restoration of flow 10Mhz BMU images and 8Mhz CWD velocity spectra of carotid artery blood flow were obtained.

CHIEF OUTCOME MEASURES

The detection of intimal flaps, thrombus, stenoses or other errors of surgical technique likely to result in perioperative morbidity.

MAIN RESULTS

CWD and BMU images were technically inadequate in 9% and 24% of cases respectively and neither technique altered clinical management. Angioscopy demonstrated significant technical errors in 12 cases (four intimal flaps, thrombus in eight). TCD detected shunt malfunction in 13% of patients, emboli during dissection in 23% and early postoperative carotid artery thrombosis in three patients.

CONCLUSIONS

A combination of TCD monitoring and completion angioscopy provided the maximum yield in terms of diagnosing technical error and establishing the cause of perioperative morbidity.

Transcranial Doppler sonography indicates critical brain perfusion during hemorrhagic hypotension in dogs

This study investigated the effects of hemorrhagic hypotension on cerebral blood flow velocity and brain electrical activity (by electroencephalogram [EEG]). Eleven mongrel dogs were anesthetized with isoflurane (1 minimum alveolar anesthetic concentration [MAC]) and catheters were placed into both femoral arteries and veins for mean arterial blood pressure (MAP) measurement, blood withdrawal, and drug administration. Brain temperature, arterial blood gases, and pH were maintained constant. EEG was recorded from temporoparietal recording sites versus a frontal reference. A pulsed transcranial Doppler (TCD) probe (2 MHz, Transpect, Medasonics) was placed on the dura via a temporal bone window to measure mean (Vmean, cm/s) and diastolic blood flow velocity (Vdiast, cm/s) in the middle cerebral artery. At the end of the surgical preparation, isoflurane was discontinued and all animals received fentanyl (bolus, 25 micrograms/kg intravenously (IV); infusion, 50 micrograms.kg-1.h-1 IV) plus 50% N2O/O2 during 30 min of equilibration. After recordings of baseline data, the dogs were hemorrhaged at a rate of 80-100 mL/min. The observation interval was 14 min. EEG spectral edge frequency (SEF 95%) and Vmean did not change when MAP was decreased from 109 +/- 10 to 63 +/- 7 mm Hg. This indicates preserved neuronal function and intact autoregulation of cerebral blood flow. Below MAP of 49 +/- 9 mm Hg, a shift of the EEG to lower frequencies was associated with decreases in Vmean and Vdiast. EEG burst suppression occurred at a MAP of 31 +/- 7 mm Hg, paralleled by a loss of the diastolic flow velocity pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Technical issues in carotid artery surgery 1995

In reviews in the 1980s, we discussed both indications for and surgical techniques in carotid endarterectomy. Significant changes in the practice of extracranial cerebrovascular reconstruction have occurred over the past few years. The newest indications and cooperative study data have recently been discussed by Camarata and Heros in this topic review series. In this article, we aim to review the advances in operative monitoring and surgical techniques of the last decade. We would be remiss, however, not to note that the latest Asymptomatic Carotid Atherosclerosis Study data, released in September 1994, indicate that carotid endarterectomy is significantly superior to medical therapy for asymptomatic stenosis of > 60%. These data, along with the North American Symptomatic Carotid Endarterectomy Trial results, will revitalize and lend scientific validity to carotid artery reconstruction.

Prediction of tolerance to carotid artery occlusion using transcranial Doppler ultrasound

Surgical sacrifice of the carotid artery is a frequently anticipated event during the treatment of certain aneurysms and tumors. The ability to predict tolerance to carotid artery occlusion is therefore of benefit when planning procedures in which the carotid artery is at risk. A trial of carotid artery occlusion using an angiographic balloon during concurrent neurological examination or blood flow studies is an accepted method for testing tolerance, but it carries the risks of an angiogram and cannot be performed at the bedside. Transcranial Doppler ultrasound (TCD) is a noninvasive modality that permits measurement of blood velocity in cerebral vessels. The immediate effects of carotid artery occlusion on middle cerebral artery (MCA) perfusion can be obtained by insonating this artery during manual carotid artery compression. To compare the TCD response to carotid artery compression with the data obtained with more formal testing, the MCA of 22 patients was insonated during manual carotid artery compression and the results compared with the clinical tolerance to balloon occlusion in all patients and to blood flow studied by single photon emission computerized tomography before or during balloon occlusion in 14 of the 22 patients. Surgery was planned to treat giant unruptured aneurysms in 17 cases, intracranial tumors in three, a carotid-cavernous fistula in one, and a carotid artery injury in one. Fifteen patients showed a reduction in TCD flow velocities by no more than 65%; of these, 14 (93%) clinically tolerated the balloon occlusion test. Of the seven patients showing a TCD flow velocity decrease of more than 65%, six (86%) developed a transient focal deficit during the occlusion. It is concluded that the change in MCA velocity measured with TCD studies during manual carotid artery occlusion is a useful predictor of the clinical and blood flow responses to a trial of carotid artery occlusion with an angiographic balloon.

Transient ischemic attacks, carotid stenosis, and an incidental intracranial aneurysm. A decision analysis

Three patients with transient ischemic attacks (TIAs), a stenotic or ulcerating carotid lesion, and an unruptured aneurysm are discussed. Decision analysis is used in comparing treatment strategies for each patient: clipping of the aneurysm, endarterectomy, or both, with or without platelet aggregation inhibitors. Bayesian sensitivity analysis with Monte Carlo simulation is used to estimate 95% confidence limits for the difference in discounted quality-adjusted life expectancy between the treatment strategies. Platelet-inhibiting therapy is indicated for all three patients, despite the increased risk of complications from subarachnoid hemorrhage. Carotid endarterectomy cannot be recommended for any of the three patients. With regard to aneurysm surgery, a toss-up exists in one patient; in another, the aneurysm should be clipped; and in one, the decision depends on the probability that the TIAs originate from the aneurysm. Guidelines for the management of similar patients are given. For patients with TIAs, a moderate carotid stenosis, and an intracranial aneurysm that does not seem to be related to the symptoms, neither clipping of the aneurysm nor endarterectomy can be recommended with confidence; however, when the intracranial aneurysm is just as likely to be the source of the TIAs as not, clipping is recommended up to the age of 70, when the surgical risks are moderately high.