Monitoring and cerebral protection during carotid endarterectomy

Transient Retinal Ischemia During Carotid Endarterectomy Estimated by Intraoperative Visual Evoked Potential Monitoring: Technical Note

OBJECTIVE

Carotid revascularization surgery is known to carry a risk of postoperative visual deterioration associated with retinal ischemia. We checked intraoperative visual evoked potential (VEP) monitoring in carotid endarterectomy (CEA).

METHODS

Ten consecutive patients who underwent CEA in Shinshu University Hospital under total intravenous anesthesia were checked by intraoperative VEP and electroretinogram (ERG) recording in addition to somatosensory evoked potential monitoring.

RESULTS

Two of 10 patients presented decreased amplitude of VEP and ERG on the ipsilateral affected side by clamping the common carotid artery and persistent attenuation of VEP and ERG during external carotid artery occlusion, using an internal carotid shunt. These findings disappeared immediately after releasing the cervical carotid artery clamping. In the other 8 patients, VEP and ERG did not change throughout the surgery.

CONCLUSIONS

Transient retinal ischemia during even brief carotid artery occlusion in the CEA procedure could be estimated by intraoperative VEP and ERG monitoring.

Ocular blood flow by laser speckle flowgraphy to detect cerebral ischemia during carotid endarterectomy

Laser speckle flowgraphy (LSFG) is a noninvasive technique that can measure relative blood flow velocity in the optic fundus contributed by the ophthalmic artery, the main first branch originating from the internal carotid artery (ICA). The aim of this study was to assess the feasibility of ocular blood flow measurement by LSFG to detect ischemic stress due to carotid clamping during carotid endarterectomy (CEA). Nineteen patients undergoing CEA with ocular blood flow measurement by LSFG and intraoperative monitoring (IOM) were prospectively enrolled between August 2016 and March 2019. The mean blur rate (MBR) of ocular blood flow by LSFG, representing relative blood flow of the branch of the retinal artery originating from the optic nerve head, was compared between before and after carotid clamping during CEA. The correlation between the reduction ratio of MBR and the regional saturation oxygen (rSO₂) index by near infrared spectroscopy was investigated. Ocular blood flow measurement by LSFG could not be performed in one patient with a severe cataract. In the other 18 patients, LSFG could be performed in all 106 sessions during surgery. The MBR reduction ratio between before and after carotid clamping ranged from - 12 to 100%. The MBR reduction ratio was positively correlated with the rSO₂ index (r = 0.694, 95% confidence interval: 0.336-0.877, p = 0.001). The MBR reduction ratio of ocular blood flow by LSFG after carotid clamping was significantly correlated with the rSO₂ index. The ocular blood flow by LSFG could be considered an adjunct modality for evaluating cerebral ischemic tolerance during CEA.

Cerebral Oximetry Monitoring During Carotid Endarterectomy: Effect of Carotid Clamping and Shunting

Cerebral oximetry is a simple method of measuring regional cerebral oxygen saturation (rSO2). One promising application is its use during carotid endarterectomy (CEA) to help minimize the risk of perioperative stroke. The authors used the INVOS-4100 cerebral oximeter at several steps during CEA to measure the effect of carotid clamping and shunting on rSO2. The authors prospectively evaluated 42 consecutive CEAs in 40 patients. All had CEA under general anesthesia with the routine use of a Javid shunt. The INVOS-4100 oximeter was used to measure rSO2 before clamping (t1), after clamping but before shunting (t2), 5 minutes after shunt insertion (t3), and after patch closure with reestablished flow (t4). The Wilcoxon signed-rank and rank-sum tests were used for analysis. Clamping of the internal carotid artery (t1 vs t2) resulted in a drop of ipsilateral rSO2 by –12.3% (p<0.001). Shunt insertion (t2 vs t3) increased rSO2 by 10.9% (p< 0.001). Contralateral rSO2 for the same time periods was insignificant. Patients with preoperative neurologic symptoms had a greater decrease in rSO2 after clamping (–18.4%) compared with a decrease of –10.4% in asymptomatic patients (p=0.037). Cerebral oximetry monitoring is simple and inexpensive. The study showed statistically significant changes in rSO2 as a result of clamping and shunting of the carotid artery. Symptomatic patients had a greater drop in rSO2.

Is Near-Infrared Spectroscopy a Reliable Method to Evaluate Clamping Ischemia during Carotid Surgery?

Guidelines do not include cerebral oximetry among monitoring for carotid endarterectomy (CEA). The purpose of this study was to evaluate the reliability of near-infrared spectroscopy (NIRS) in the detection of clamping ischemia and in the prevention of clamping-related neurologic deficits using, as a cutoff for shunting, a 20% regional cerebral oxygen saturation (rSO(2)) decrease if persistent more than 4 minutes, otherwise a 25% rSO(2) decrease. Bilateral rSO(2) was monitored continuously in patients undergoing CEA under general anesthesia (GA). Data was recorded after clamping, declamping, during shunting and lowest values achieved. Preoperative neurologic, CT-scan, and vascular lesions were recorded. We reviewed 473 cases: 305 males (64.5%) mean age 73.3 ± 7.3. Three patients presented transient ischemic deficits at awakening, no perioperative stroke or death; 41 (8.7%) required shunting: 30 based on the initial rSO(2) value and 11 due to a decrease during surgery. Using the ROC curve analysis we found, for a >25% reduction from baseline value, a sensitivity of 100% and a specificity of 90.6%. Reliability, PPV, and NPV were 95.38%, 9%, and 100%, respectively. In conclusion, this study indicates the potential reliability of NIRS monitoring during CEA under GA, using a cutoff of 25% or a cutoff of 20% for prolonged hypoperfusion.

Near-infrared spectroscopy as an index of brain and tissue oxygenation

Continuous real-time monitoring of the adequacy of cerebral perfusion can provide important therapeutic information in a variety of clinical settings. The current clinical availability of several non-invasive near-infrared spectroscopy (NIRS)-based cerebral oximetry devices represents a potentially important development for the detection of cerebral ischaemia. In addition, a number of preliminary studies have reported on the application of cerebral oximetry sensors to other tissue beds including splanchnic, renal, and spinal cord. This review provides a synopsis of the mode of operation, current limitations and confounders, clinical applications, and potential future uses of such NIRS devices.

Current status of carotid endarterectomy and stenting for symptomatic carotid stenosis

There is still considerable uncertainty about the place of carotid stenting in patients with recently symptomatic carotid bifurcation stenosis. Most reviews of carotid endarterectomy versus carotid stenting concentrate on technical aspects and advances in stenting, but the techniques involved in both carotid endarterectomy and stenting are evolving. In addition to reviewing the results of the various randomised controlled trials of carotid endarterectomy versus stenting for symptomatic carotid stenosis, this review considers recent advances and current best practice for endarterectomy. Ongoing randomized trials will determine whether or not the procedural risk of stroke and death is definitely lower with endarterectomy than with stenting, but the key issue that remains to be determined reliably is how the procedural risks of stenting vary with patient characteristics - perhaps the most important question being not whether endarterectomy is better than stenting or vice versa, but for whom is one technique likely to be better than the other.

A clinical evaluation of near-infrared cerebral oximetry in the awake patient to monitor cerebral perfusion during carotid endarterectomy

STUDY OBJECTIVE

To evaluate the relationship between continuous noninvasive monitoring of cerebral saturation (regional cerebral oxygen saturation [rSo2]) and occurrence of clinical and electroencephalographic (EEG) signs of cerebral ischemia during carotid cross-clamping.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PATIENTS

Fifty ASA physical status II and III inpatients undergoing elective carotid endarterectomy with a cervical plexus block.

INTERVENTIONS

rSo2 was continuously monitored throughout surgery, while an independent neurologist evaluated the occurrence of both clinical and EEG signs of cerebral ischemia induced during carotid cross-clamping.

MEASUREMENTS AND MAIN RESULTS

rSo2 was recorded 1 and 3 minutes after clamping the carotid artery during a 3-minute clamping test. In 5 patients (10%), the carotid clamping test was associated with the occurrence of clinical and EEG signs of cerebral ischemia. All these patients were treated with the placement of a Javid shunt, which completely resolved the symptoms. In no patient was permanent neurological injury reported at hospital discharge. In 4 of these patients, EEG signs of cerebral ischemia were present at both observation times, and in one of them, the duration of cerebral ischemia was less than 2 minutes. The percentage rSo2 reduction from baseline during the carotid clamping test was 17% +/- 4% in patients requiring shunt placement and only 8% +/- 6% in those who did not require it (P = .01). A decrease in rSo2 15% or greater during the carotid clamping test was associated with a 20-fold increase in the odd for developing severe cerebral ischemia (odds ratio, 20; 95% confidence interval, 6.7-59.2) (P = .001); however, this threshold had a 44% sensitivity and 82% specificity, with only 94% negative predictive value.

CONCLUSIONS

Continuous rSo2 monitoring is a simple and noninvasive method that correlates with the development of clinical and EEG signs of cerebral ischemia during carotid cross-clamping; however, we could not identify an rSo2 threshold that can be used alone to predict the need for shunt placement because of the low sensitivity and specificity.

Evaluation of Quality Improvement Interventions for Reducing Adverse Outcomes of Carotid Endarterectomy

BACKGROUND

Clinical and health services interventions should be evaluated for their effectiveness.

OBJECTIVES

The objectives of this study were to evaluate the effectiveness of quality improvement interventions for reducing the adverse outcome of the carotid endarterectomy (CEA) procedure, and to study the relationship between pre- and postintervention 30-day mortality and stroke rates. These interventions were implemented in 1997-1998 by the Peer Review Organizations (PRO) for 7 states.

RESEARCH DESIGN

In a quasiexperimental study, a control state was matched with each of the 7 intervention states. Pretest-posttest analyses compared the preintervention outcome rates in each intervention and control state with the corresponding postintervention rates. In a time (1991-2001) series analysis, the trends in the preintervention 30-day, 7-state mortality in intervention and control states were compared with the trends in the corresponding postintervention rates.

STUDY POPULATION

We studied Medicare beneficiaries aged 65 years and older who had a CEA procedure in 14 states during 1991-2001.

RESULTS

There was no correlation between the state-specific, preintervention 30-day mortality and the corresponding postintervention mortality. After interventions, there was no significant decline in 30-day mortality in any intervention or control state, or in all 7 intervention states combined or all control states combined. Similarly, the 30-day stroke rate did not decrease after interventions in any state. The trend in the 7-state, 30-day mortality also did not show further decline after interventions.

CONCLUSION

After PRO interventions, the post-CEA 30-day mortality and stroke rates did not decrease in any individual intervention state or in all states combined.

Carotid artery disease and stroke during coronary artery bypass: a critical review of the literature

OBJECTIVES

to determine the role of carotid artery disease in the pathophysiology of stroke after coronary artery bypass (CABG).

DESIGN

systematic review of the literature.

RESULTS

the risk of stroke after CABG was 2% and remained unchanged between 1970-2000. Two-thirds occurred after day 1 and 23% died. 91% of screened CABG patients had no significant carotid disease and had a <2% risk of peri-operative stroke. Stroke risk increased to 3% in predominantly asymptomatic patients with a unilateral 50-99% stenosis, 5% in those with bilateral 50-99% stenoses and 7-11% in patients with carotid occlusion. Significant predictive factors for post-CABG stroke included; (i) carotid bruit (OR 3.6, 95% CI 2.8-4.6), (ii) prior stroke/TIA (OR 3.6, 95% CI 2.7-4.9) and (iii) severe carotid stenosis/occlusion (OR 4.3, 95% CI 3.2-5.7). However, the systematic review indicated that 50% of stroke sufferers did not have significant carotid disease and 60% of territorial infarctions on CT scan/autopsy could not be attributed to carotid disease alone.

CONCLUSIONS

carotid disease is an important aetiological factor in the pathophysiology of post-CABG stroke. However, even assuming that prophylactic carotid endarterectomy carried no additional risk, it could only ever prevent about 40-50% of procedural strokes.

Transcranial oximetry as a new monitoring method for HEMS (Helicopter EMS)

INTRODUCTION

Transcranial oximetry (TCO) is a new method to measure continuous changes in brain blood oxygen saturation (rSO2) by using near-infrared spectroscopy (NIRS). To our knowledge, no studies about TCO in air medical transport have been published.

METHODS

Twenty healthy volunteers (HEMS medical crew) were investigated during flight missions without patients. We measured oxygen saturation (SpO2), cardiac rate, and rSO2 with an INVOS 4100 Cerebral Oximeter at sea level and at each 1000 feet until we reached a flight level of 5000 feet.

RESULTS

The oximeter did not produce any interference with medical or aeronautical equipment. Subjects' SpO2 showed a slight decrease with altitude (P < 0.010), but rSO2 remained constant (P = 0.28), with little delay in the physiological correction of SpO2 and rSO2 values.

CONCLUSION

TCO may play an important role in the development of new monitoring methods for critical patients in air medical transport. Further studies with large sample sizes and patients are necessary to generalize findings.

A policy of quality control assessment helps to reduce the risk of intraoperative stroke during carotid endarterectomy

OBJECTIVES

A pilot study in our unit suggested that a combination of transcranial Doppler (TCD) plus completion angioscopy reduced incidence of intra-operative stroke (i.e. patients recovering from anaesthesia with a new deficit) during carotid endarterectomy (CEA). The aim of the current study was to see whether routine implementation of this policy was both feasible and associated with a continued reduction in the rate of intraoperative stroke (IOS).

MATERIALS AND METHODS

Prospective study in 252 consecutive patients undergoing carotid endarterectomy between March 1995 and December 1996.

RESULTS

Continuous TCD monitoring was possible in 229 patients (91%), while 238 patients (94%) underwent angioscopic examination. Overall, angioscopy identified an intimal flap requiring correction in six patients (2.5%), whilst intraluminal thrombus was removed in a further six patients (2.5%). No patient in this series recovered from anaesthesia with an IOS, but the rate of postoperative stroke was 2.8%.

CONCLUSIONS

Our policy of TCD plus angioscopy has continued to contribute towards a sustained reduction in the risk of IOS following CEA, but requires access to reliable equipment and technical support. However, a policy of intraoperative quality control assessment may not necessarily alter the rate of postoperative stroke.

Quality control during carotid endarterectomy

Although some form of quality control assessment is standard practice following virtually all forms of peripheral vascular reconstruction, it is seldom applied to carotid endarterectomy. This is despite the fact that the complications following endarterectomy can be catastrophic, are often related to technical error and are not easily remedied. A number of novel quality control techniques are now available. This review article summarizes the application of these methods to ensuring optimal surgical practice in patients undergoing carotid endarterectomy.

Preoperative carbon dioxide reactivity studies do not predict the hemodynamic changes seen during carotid endarterectomy after internal carotid artery clamping

BACKGROUND AND PURPOSE

A preoperative warning of progressive cerebral ischemia during surgery may be of use in planning carotid endarterectomy (CE). We have set out to determine whether preoperative cerebrovascular reactivity studies predict the late hemodynamic changes detected during the procedure.

PATIENTS AND METHODS

Sixty-seven patients awaiting CE for high-grade carotid stenosis underwent preoperative cerebral CO(2) reactivity assessment using standard transcranial Doppler (TCD) methods. During subsequent surgery, hemodynamic changes were monitored with TCD, near-infrared spectroscopy, and a cerebral function monitor. Signals of mean MCA flow velocity (FV) and of cerebral oxyhemoglobin and deoxyhemoglobin concentration were recorded continuously, and the mean values were measured at 5, 10, and 15 minutes after internal carotid clamping. For each variable, the maximum signal change was measured 5 minutes after clamp application (Max(5)), and in addition the spontaneous hemodynamic recovery over the next 10 minutes (I(rec)) was calculated. Scatterplots of Max(5) and I(rec) against preoperative CO(2) reactivity indices (ipsilateral, bihemispheric mean, and interhemispheric assymmetry) were generated for correlative analysis.

RESULTS

The Max(5) for oxyhemoglobin and deoxyhemoglobin were inversely related (r=-.302, P=.015). There was no relationship between ipsilateral preoperative CO(2) reactivity index and Max(5) for any intraoperative variable measured. In addition, the reactivity did not predict the hemodynamic recovery (I(rec)) observed during clamp application. However, the interhemispheric asymmetry did show a modest inverse correlation to Max(5) FV (r=-.256, P=.046).

CONCLUSION

Preoperative TCD cerebral CO(2) reactivity cannot be used clinically to predict the intraoperative hemodynamic changes seen during CE.

Experience with transcranial Doppler monitoring reduces the incidence of particulate embolization during carotid endarterectomy

BACKGROUND

The aim of this study was to investigate whether the introduction of routine transcranial Doppler (TCD) ultrasonography during carotid endarterectomy reduces the incidence of microembolization by altering operative technique.

METHODS

The number and nature of microemboli detected during the first 75 consecutive carotid endarterectomies performed with TCD monitoring during 1992-1993 (group 1) were compared with those in a similar series of 75 consecutive patients undergoing carotid endarterectomy in 1995 (group 2), after substantial experience (210 patients) with TCD monitoring. Emboli were classified as either particulate or gaseous.

RESULTS

In patients with evidence of particulate emboli during the dissection phase of the operation, the total number of particulate emboli fell significantly in patients in group 2 (P = 0.019). Similarly, in patients in whom microembolization was detected on immediate opening of the shunt, the total number of microemboli also fell significantly in group 2 (P = 0.003). Overall, the median (95 per cent confidence interval) number of particulate emboli detected during the entire procedure fell significantly from 21 (16-29) in group 1 to 9 (7-14) in group 2 (P = 0.0008).

CONCLUSIONS

TCD monitoring plays an important role in the training and quality control of carotid endarterectomy and helps significantly to reduce the amount of microembolization.

Prevention of postoperative thrombotic stroke after carotid endarterectomy: the role of transcranial Doppler ultrasound

PURPOSE

To determine the incidence of particulate embolization after carotid endarterectomy (CEA), the effect of dextran-40 infusion in patients with sustained postoperative embolization, and the impact of transcranial Doppler (TCD) monitoring plus adjuvant dextran therapy on the rate of postoperative carotid thrombosis.

METHODS

Prospective study in 100 patients who underwent CEA with 6-hour postoperative monitoring using a TCD that was modified to allow automatic, intermittent recording from the ipsilateral middle cerebral artery waveform (10 minute sample every 30 minutes). An incremental dextran-40 infusion was commenced if 25 or more emboli were detected in any 10-minute period.

RESULTS

Overall, 48% of patients had one or more emboli detected in the postoperative period, particularly in the first 2 hours. However, sustained embolization that required Dextran therapy developed in only five patients. In each case, the rate of embolization rapidly diminished.

CONCLUSIONS

A small proportion of patients have sustained embolization after CEA, which in previous studies has been shown to be highly predictive of thrombotic stroke. Intervention with dextran reduced and subsequently stopped all the emboli in those in whom it was used and contributed to a 0% perioperative morbidity and mortality rate in this series.

Inadequate cerebral perfusion is an unlikely cause of perioperative stroke

The purpose of this study was to determine the importance of hypoperfusion ischemia as a cause of stroke during carotid endarterectomy (CEA). A retrospective analysis of 128 consecutive CEA procedures were examined in patients at risk for hypoperfusion ischemia, namely, patients with occlusion of the contralateral carotid artery. All procedures were performed under general anesthesia without the use of a temporary indwelling shunt. Sixty-one percent of patients had cerebrovascular symptoms preoperatively and 39% were asymptomatic. The degree of stenosis of the carotid artery was 80%-99% in 67% (86/128) of patients, 60%-79% in 25% (32/128), 20%-59% in 7% (9/128), and 0-19% in 0.8% (1/128). The perioperative mortality was 0.8% (1/128), the incidence of permanent neurologic morbidity was 1.6% (2/128), and the incidence of transient neurologic morbidity was 3.9% (5/128). In conclusion, these data suggest that hypoperfusion ischemia is a rare cause of stroke during CEA even in patients with occlusion of the contralateral carotid artery and that CEA can be performed safely even in patients with contralateral occlusion without the use of a temporary indwelling shunt.

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.

Intraoperative transcranial Doppler sonography monitoring during carotid surgery under locoregional anaesthesia

OBJECTIVES

Studies comparing transcranial Doppler ultrasonography (TCD) with other intraoperative monitoring techniques for detecting clamping ischaemia during carotid endarterectomy under general anaesthesia suggest that a reduction of > two-thirds in the mean middle cerebral artery velocity (mMCAv) or a reduction of > 0.4 in the preclamping mMCAv: clamping mMCAv ratio warrants cerebral protection. Our aim was to study the relationship between mMCAvs and clamping ischaemia during carotid endarterectomy in awake patients.

MATERIALS AND METHODS

In a consecutive series of 57 patients undergoing carotid endarterectomy under locoregional anaesthesia 51 were monitored by intraoperative TCD, continuous EEG, and neurologic awake testing.

RESULTS

Five of the 51 (9.8%) patients had transient clamping ischaemia, which carotid shunting reversed. TCD showed that these five patients had significant lower mean mMCAvs than the other 46 patients, who had no deficits (1.8 +/- 1.1 cm/s vs. 26.2 +/- 8.5, p = 0.0003). Current TCD criteria indicated that four other patients (7.8%) should have been shunted. All four had significantly higher clamping mMCAvs than the five shunted patients (11.5 +/- 1.9 vs. 1.8 +/- 1.1, p = 0.0012).

CONCLUSIONS

Intraoperative TCD detected cerebral ischaemia and yielded no false-negative. An mMCAv of 10 cm/s or less may indicate the risk of clamping ischaemia better than the higher threshold currently proposed. This would avoid unnecessary shunting due to false-positives.

Somatosensory evoked potential monitoring during carotid surgery

Controversy exists over the value of intraoperative monitoring and shunting in patients undergoing carotid endarterectomy. Although it is widely believed that contralateral carotid occlusion and previous stroke mandate intraoperative shunting, the susceptibility of these two groups of patients to cerebral ischemia during carotid artery endarterectomy is not well defined. Somatosensory evoked potentials (SSEPs) were monitored in 113 carotid artery endarterectomy patients. Of these, 32 (28.3%) had a previous stroke, 24 (21.2%) had a contralateral carotid occlusion and 33 (29.2%) were diabetic. There were no deaths and only one perioperative stroke (0.9%). Cerebral ischemia occurred in 14 patients (12.4%). Six of these patients had a contralateral carotid occlusion. Some 29 patients (25.7%) were shunted, including 10 with contralateral carotid occlusions that did not have major SSEP changes. In the latter half of the study, 14 patients with contralateral carotid occlusions were selectively shunted (six shunted, eight not shunted) with no neurological complications. Thirty-two patients with prior strokes were selectively shunted (nine shunted, 23 not shunted); of these, one shunted patient undergoing combined carotid artery endarterectomy and coronary artery bypass grafting had a perioperative stroke. Intraoperative monitoring with SSEPs accurately identifies cerebral ischemia secondary to carotid clamping as well as patients requiring shunts. With use of intraoperative SSEP monitoring, selective shunting may be safely performed in patients with a contralateral carotid occlusion or a previous stroke.

Assessment of intracranial primary collaterals using transcranial color-coded real-time sonography

Transcranial color-coded sonography (TCCS) was used to assess primary willisian collaterals in 100 patients with extracranial internal carotid artery (ICA) stenosis. Their importance was determined during carotid endarterectomy (CEA) by transcranial Doppler measurement of blood flow velocity in the ipsilateral middle cerebral artery (MCAV) before and after carotid clamping. All patients had unilateral ICA disease of at least 60% stenosis. Twenty-nine ICAs (14.5%) were occluded, 70 vessels (35%) were stenosed by 80 to 99%, 43 vessels (21.5%) were stenosed by 60 to 79%, and 53 ICAs had stenosis of less than 60%. Temporal hyperostosis precluded TCCS in 15 patients (15%). Anterior cerebral/communicating artery collaterals were detected in 40 patients (49%) and posterior cerebral/communicating artery collaterals were detected in 22 patients (27%). No patients with ICA stenosis of less than 80% had established collateral pathways. Patients with willisian collaterals showed higher postclamp MCAVs as a proportion of the preclamp value during CEA (72% [62-81]; median with 95% confidence interval) than did those without primary collaterals (46% [34-58], p = 0.02). TCCS allows noninvasive assessment of intracranial primary collaterals whose functional importance is recognized during abrupt hemodynamic challenge. It may determine which patients are at greatest risk of ischemia during cerebral revascularization.

Effect of intermittent reperfusion and nitric oxide synthase inhibition on infarct volume during reversible focal cerebral ischemia

The authors examined the effects of both intermittent reperfusion and nitric oxide synthase (NOS) inhibition, caused by NG-nitro-L-arginine methyl ester (L-NAME) during episodes of focal cerebral ischemia induced to simulate the neurosurgical setting. Seventy-eight Wistar rats underwent single (60 minutes of ischemia) or repetitive (four 15-minute periods of ischemia separated by 5 minutes of reperfusion) episodes of middle cerebral artery occlusion while under anesthesia (1.0% halothane). Twenty-four hours after the procedure, the animals were given neurological examinations and then sacrificed for histological preparation and examination. The intermittent reperfusion groups tended to have smaller mean cortical infarctions. There was also a trend showing a decrease in infarction size in groups given L-NAME. The combination of intermittent reperfusion and preischemic administration of L-NAME (10 mg/kg) resulted in a 65% reduction in infarction size (p < 0.05) when compared to that caused by 60 minutes of single occlusion without L-NAME. The use of NOS inhibition combined with intermittent reperfusion may be a technique to provide intraoperative cerebral protection during neurovascular procedures that require temporary vascular occlusion.

Effects of intermittent reperfusion on brain pHi, rCBF, and NADH during rabbit focal cerebral ischemia

BACKGROUND AND PURPOSE

The use of intermittent reperfusion versus straight occlusion during neurovascular procedures is controversial. This experiment studied the effects of intermittent reperfusion and single occlusion on intracellular brain pH (pHi), regional cerebral or cortical blood flow, and nicotinamide adenine dinucleotide (NADH) fluorescence during temporary focal ischemia.

METHODS

Twenty fasted rabbits under 1.0% halothane anesthesia were divided into four groups: (1) nonischemic controls, (2) 60 minutes of uninterrupted focal ischemia, (3) 2 x 30-minute periods of focal ischemia separated by a 5-minute reperfusion, and (4) 4 x 15-minute periods of focal ischemia separated by three 5-minute reperfusion periods. Focal ischemia was produced by occlusion of both the middle cerebral and ipsilateral anterior cerebral arteries. After the final occlusion, there was a 3-hour reperfusion period in all groups. Regional cerebral and cortical blood flow, brain pHi, and NADH fluorescence were measured with in vivo panoramic fluorescence imaging.

RESULTS

During occlusion, regional cerebral and cortical blood flows and NADH fluorescence values were not different among the groups. Brain pHi was significantly lower in the 4 x 15-minute group compared with the 1 x 60-minute group (6.57 +/- 0.02 versus 6.73 +/- 0.06; P < .03) but not significant when compared with the 2 x 30-minute group. During the short reperfusion periods, all parameters returned to normal except for NADH fluorescence levels, which remained elevated. During the postischemic final reperfusion period, there was a mild brain alkalosis of approximately 7.1 in all groups. There were no significant differences in NADH fluorescence among groups during the final reperfusion. Regional cerebral and cortical blood flow returned to near normal values in all groups.

CONCLUSIONS

This study demonstrates that intermittent reperfusion during temporary focal ischemia has different effects on the intracytoplasmic and the intramitochondrial compartments: worsening of brain cytoplasmic pHi but no significant differences in the oxidation/reduction level of mitochondrial NADH.

Cerebral hypoxia detected by near infrared spectroscopy

Near infrared spectroscopy is a relatively new technique for monitoring intracerebral oxygen saturation. Using the technique, three episodes of cerebral hypoxia were detected during elective carotid endarterectomy which were not reliably recorded by more standard monitoring of cerebral perfusion. In one case, cerebral hypoxia was related to slippage of the tracheal tube into the right main bronchus and in the other two to episodes of hypotension. Near infrared spectroscopy is a reliable indicator of peripheral cortical perfusion and provides continuous and noninvasive monitoring of intracerebral oxygen saturation.

Intraoperative duplex monitoring of the carotid bifurcation for the detection of technical defects

OBJECTIVES

Intraoperative Duplex examination can be used to identify technical imperfections during carotid endarterectomy. The objectives of this study were: (1) to evaluate the technical feasibility of intraoperative Duplex; (2) to compare Duplex findings with contrast arteriography; (3) to correlate intraoperative Duplex findings with postoperative complications and with Duplex data obtained during follow-up.

DESIGN

Prospective clinical study.

SETTING

Department of Vascular Surgery, Catharina Hospital, Eindhoven, The Netherlands.

MATERIALS

44 patients underwent Duplex scanning at the completion of carotid endarterectomy. In addition intraoperative arteriography was performed in the first 16 consecutive patients. Follow-up included a Duplex examination at three monthly intervals during the first postoperative year.

OUTCOME MEASURES

Technical defects and flow disturbance at the time of surgery, and postoperative restenosis.

RESULTS

At contrast arteriography a distal intimal ridge with 15-20% diameter reduction was observed in two, an occlusion of the external carotid artery in three and moderate kinking in one patient. All abnormalities were identified at Duplex imaging. In none of the cases were the Duplex findings considered an indication to re-explore the endarterectomised internal carotid artery. Postoperative complications occurred in six patients: three strokes, two transient ischaemic attacks and two internal carotid occlusions (in one patient combined with a stroke). Severe spectral broadening (spectral class D) correlated significantly with early postoperative complications (p = 0.027). In contrast, moderate defects on Duplex imaging did not correlate significantly with early complications. Duplex examination during the first year of follow-up demonstrated recurrent stenosis in four patients. Intraoperative spectral broadening did not correlate significantly with the development of common or internal carotid restenosis. However, external carotid recurrent stenosis was positively related to intraoperative flow disturbance (p = 0.0003).

CONCLUSION

Duplex scanning is easy to use after completion of carotid endarterectomy. There is good agreement between intraoperative Duplex scanning and contrast arteriography. Extensive spectral broadening of the Doppler velocity signal is associated with an increased prevalence of early postoperative complications. Restenosis at follow-up appears to be related to severe flow disturbance as was demonstrated for the external carotid artery.

On-table diagnosis of incipient carotid artery thrombosis during carotid endarterectomy by transcranial Doppler scanning

We present a case where transcranial Doppler ultrasound monitoring of a carotid endarterectomy enabled us to detect the incipient thrombosis of the operated artery before reversal of anesthesia. The use of transcranial Doppler ultrasound monitoring in carotid endarterectomy has the potential to detect this complication before serious neurologic damage has occurred and therefore reduce the morbidity and mortality rates associated with the operation.

Cerebral oxygen saturation, transcranial Doppler ultrasonography and stump pressure in carotid surgery

Transcranial Doppler ultrasonography (TCD) of the middle cerebral artery (MCA), light-reflective cerebral oximetry and measurement of internal carotid artery stump pressure were compared as methods of monitoring cerebral perfusion during carotid surgery in 33 patients. Median cerebral oxygen saturation was 70 (range 62-85) per cent and TCD-measured mean blood velocity 42 (range 19-91) cm/s before carotid cross-clamping, falling to 68 (53-83) per cent and 16 (0-50) cm/s respectively on application of the clamps (P < 0.001). Stump pressure correlated closely with MCA blood velocity 30 s after the start of cross-clamping (rs = 0.58, P < 0.001), but not with cerebral oxygen saturation. A fall of 5 per cent or more in cerebral oxygen saturation following cross-clamp application was predicted by a decrease in mean MCA blood velocity of at least 60 per cent. Changes in cerebral oxygen saturation correlated significantly with systolic blood pressure throughout the perioperative period (rs = 0.41, P < 0.001). Significant falls in cerebral oxygenation were not predicted by low stump pressure but were associated with large reductions in the mean MCA blood velocity measured by TCD.

Role of completion angioscopy in detecting technical error after carotid endarterectomy

Completion fibreoptic angioscopy was performed in 30 consecutive patients after carotid endarterectomy. The aim was to evaluate the potential role of angioscopy as a quality-control technique. Major abnormalities (two initial flaps, two large thrombi) were identified in four patients and minor adherent thrombus was encountered in five. All abnormalities were corrected before restoration of flow. This preliminary experience suggests that completion angioscopy merits further study as a method for the intraoperative detection of potentially harmful lesions after carotid endarterectomy.