G.H. Visser

Recurrent ischemia in symptomatic carotid occlusion Prognostic value of hemodynamic factors

Objective: To identify hemodynamic factors that predict recurrence of ipsilateral cerebral ischemic events in patients with symptomatic carotid artery occlusion (CAO). Patients and Methods: The authors studied 117 consecutive patients with CAO and corresponding recent (≤6 months) ischemic symptoms of the brain or eye that were transient or at most mildly disabling. They determined, using Cox proportional hazards analysis, the prognostic value for recurrence of ipsilateral cerebral ischemic events of 1) clinical features believed to indicate hemodynamic compromise, 2) collateral blood flow pattern, and 3) transcranial Doppler CO2-reactivity. Results: None of the 24 patients with symptoms of retinal ischemia alone had a recurrent cerebral ischemic event. In the 93 patients with cerebral ischemic symptoms on entry, recurrence of these symptoms was independently predicted by 1) the nature of the initial symptoms being of purported hemodynamic origin (limb-shaking, precipitation of symptoms by rising, exercise or low blood pressure, retinal claudication) (hazard ratio [HR] 3.8, 95% CI 1.5 to 9.5), 2) continuing symptoms after the CAO had been documented, but before inclusion in the study (HR 5.9, 95% CI 2.2 to 16.1), and 3) the presence of collateral blood flow via leptomeningeal vessels (HR 4.1, 95% CI 1.3 to 13.1). CO2-reactivity did not predict recurrence of cerebral ischemic events. Conclusions: Having cerebral in contrast to retinal ischemia, clinical features suggestive of hemodynamic compromise, continuing symptoms after demonstration of the CAO, and presence of leptomeningeal collaterals may help to identify patients with symptomatic CAO at high risk of future cerebral ischemia.

Changes in Cerebral Oxygen Uptake and Cerebral Electrical Activity During Defibrillation Threshold Testing

During cardioverter-defibrillator implantation, repeated episodes of ventricular fibrillation (VF) are induced. Insufficient recovery of oxygen metabolism may cause neurological sequelae. In this prospective clinical study, we monitored the electroencephalogram (EEG), middle cerebral artery blood flow velocity (Vmca), and jugular bulb oxygen saturation and estimated cerebral oxygen uptake. Results were analyzed for tests requiring a single shock (Group 1) and tests requiring multiple shocks for defibrillation (Group 2). Immediately after the induction of VF, the mean arterial blood pressure (MAP) decreased to <30 mm Hg, and the Vmca decreased to 0 cm/s. The EEG showed ischemic changes consisting of a decrease of fast, and an increase of slow, activity, progressively declining to isoelectricity within 11 +/- 2 s. After defibrillation, the MAP recovered rapidly regardless of the arrest duration (3 +/- 2 s). The EEG recovered within 17 +/- 9 and 22 +/- 12 s, respectively, for Groups 1 and 2 (P < 0.05) and did not reveal ischemic changes until induction of a subsequent arrest. In Group 1, the cerebral oxygen uptake increased to 191% +/- 31% of baseline values and returned to baseline in 16 +/- 7 s, whereas in Group 2, it increased to 229% +/- 38% (P < 0.05), followed by a significant decrease to less than baseline (85% +/- 18%; P < 0.005), and returned to baseline simultaneously with the Vmca. We conclude that, although restoration to normal of the EEG and cerebral oxygen uptake coincide in short arrests, EEG recovery underestimates metabolic recovery after tests requiring multiple shocks. Implications: Short test intervals have been mentioned as a cause of neurological sequelae after cardioverter-defibrillator implantation. This study demonstrates that although all systemic hemodynamic variables and the electrocardiogram may have returned to normal, cerebral oxygen uptake may still be depressed for a considerable time, especially after tests requiring two or more shocks. (Anesth Analg 1998;87:16-20)

Bilateral Increase in CO2 Reactivity After Unilateral Carotid Endarterectomy

BACKGROUND AND PURPOSE A low or absent CO2 reactivity is considered indicative of a compromised hemodynamic compensatory capacity in patients with internal carotid artery (ICA) stenosis or occlusion. The aim of the present study was to investigate whether patients with preoperatively decreased or absent CO2 reactivity show an improvement of CO2 reactivity 3 months after carotid endarterectomy (CEA) and whether the preoperative CO2 reactivity is correlated with clinical classification and hemodynamic factors. METHODS A group of 65 patients with > 70% ICA stenosis was studied. CO2 reactivity was measured by bilateral transcranial Doppler sonography before and 3 months after CEA. RESULTS The preoperative CO2 reactivity was not significantly different in subgroups formed according to the presenting clinical symptoms. Patients with severe ICA stenosis with contralateral ICA occlusion had mean low preoperative CO2 reactivity on both sides. Furthermore, patients with reversed flow in the ophthalmic artery had low mean preoperative CO2 reactivity on the same side. The CO2 reactivity was not significantly different in the subgroups of patients with signs of collateral blood flow through the anterior or posterior communicating artery. In particular, patients with low preoperative CO2 reactivity (approximately < 30%) showed an evident increase after the operation. Such an inverse correlation was found bilaterally, although it was more pronounced on the CEA side. CONCLUSIONS CEA can increase CO2 reactivity in both hemispheres. This effect is most pronounced in patients with low (< 30%) preoperative CO2 reactivity. If this group represents patients who would be at risk from low-flow stroke, then testing of CO2 reactivity might help select a subset of patients with an especially high probability of benefit from CEA.

Carotid endarterectomy monitoring: patterns of spectral EEG changes due to carotid artery clamping

OBJECTIVE The purpose of the study was to make an objective and quantitative analysis of the EEG changes caused by carotid artery clamping during carotid endarterectomy (CEA) monitoring. METHODS Factor analysis was used to study the intraoperative spectral EEG changes in 94 patients during clamping of the carotid artery. In addition, the relation between the extracted factors and the changes in blood pressure and blood flow velocity in the middle cerebral artery during clamping was studied. RESULTS Two factors were extracted with factor analysis. The first factor represented a change in power in the alpha and beta frequency ranges in combination with a less pronounced opposite change in power in the delta frequency range. The second factor represented a change in power restricted to the delta and theta frequencies. With the first factor, two types of spectral EEG changes could be distinguished: changes indicative of cerebral ischemia (decrease in fast activity and increase in slow activity) and the opposite changes suggesting cerebral activation (arousal). With the two factors combined, the changes indicative of minor ischemia (decrease in fast activity only) could also be distinguished. CONCLUSION Further study is required to test whether patients showing the EEG changes indicative of activation or minor ischemia actually require shunting.

Decreased transcranial Doppler carbon dioxide reactivity is associated with disordered cerebral metabolism in patients with internal carotid artery stenosis

PURPOSE The hemodynamic effect of stenosis of the internal carotid artery (ICA) can be assessed by measuring, with transcranial Doppler (TCD), the carbon dioxide (CO(2)) reactivity of the cerebral vessels. The aim of this study was to determine whether a decreased CO(2) reactivity is associated with a compromised cerebral metabolism, as evaluated with (1)H magnetic resonance spectroscopy (MRS). METHODS Sixty-six patients with unilateral or bilateral stenosis of the ICA, who were scheduled for carotid endarterectomy (CEA) and who had undergone both a TCD CO(2) reactivity test and a MRS examination, were included in this study. The ICA stenosis on one side (CEA side) was always more than 70%, and the extent of the stenosis on the contralateral side varied. RESULTS The CO(2) reactivity and the N-acetyl aspartate (NAA)/choline ratio were correlated in both hemispheres (r =.43; P <.001). Patients with an ICA occlusion contralateral to the CEA side are especially at risk for disordered cerebral hemodynamics and metabolism; in the contralateral hemisphere, the mean CO(2) reactivity and NAA/choline ratio were abnormal (18% and 1.52, respectively), and lactate was present in 85% of the patients. Changes indicative of disordered hemodynamics were found more often in symptomatic than in asymptomatic patients. CONCLUSION A decreased CO(2) reactivity appears to be associated with a disordered cerebral metabolism. Patients with severe bilateral ICA stenosis are at risk for disordered cerebral metabolism and hemodynamics. Therefore, the indication for CEA based on the degree of ICA stenosis and clinical grounds might be refined with an additional test, such as the TCD CO(2) reactivity test.

Lack of Evidence for a Poor Haemodynamic or Metabolic State of the Brain in Patients with Haemodynamic Clinical Features Associated with Carotid Artery Occlusion

Objective: To assess whether patients with carotid artery occlusion (CAO) who have clinical features suggesting a haemodynamic origin have a poor haemodynamic or metabolic state of the brain. Methods: In 117 patients with ischaemic symptoms of the eye or brain that were transient or at most moderately disabling and associated with a CAO, we compared CO2 reactivity, quantitative flow measurement by magnetic resonance (MR) angiography, metabolic ratios measured by 1H-MR spectroscopy, collateral blood flow patterns and the presence of infarcts of the borderzone type between patients grouped by the following clinical features: (1) presence or absence of at least one of the ‘classical’ haemodynamic symptoms: limb shaking, retinal claudication, precipitation of symptoms by exercise, by rising from a sitting or lying position, by transition from a cold to a warm environment, or by documented hypotension, and (2) symptoms having occurred after demonstration of the CAO or only before the occlusion was documented. Results: Patients with (n = 16) and without (n = 101) one of the ‘classical’ haemodynamic symptoms did not differ in any of the measured indices. Patients with recurrent symptoms after documentation of the CAO (n = 56) had lower CO2 reactivity (difference 8.3%, 95% confidence interval 0.1–16.5) than those with symptoms only before documentation of the occlusion (n = 61), whereas no significant differences were found in any of the other measured indices. The difference in CO2 reactivity was no longer significant after adjustment for the interval between the patients’ last symptoms and the CO2 reactivity measurement. Conclusion: In patients with CAO we could not find an association between symptoms that have been associated with hypoperfusion and a poor haemodynamic or metabolic state of the brain.

Increase in alpha rhythm frequency after carotid endarterectomy

OBJECTIVES Besides preventing stroke, carotid endarterectomy (CEA) is reported to improve cerebral circulation and brain function. We tested whether this improvement is reflected by changes in the qEEG. METHODS qEEG changes in 166 patients with a >70% stenosis of the internal carotid artery (ICA) were assessed after subtraction of the preoperative and postoperative spectra (eyes closed condition) before and 3 months after CEA. The mean frequency of the alpha band (MFA), the peak frequency of the alpha band (F alpha), and bands with limits relative to each patients F alpha were studied in relation to neurological symptoms, patency or occlusion of the contralateral ICA, shunt requirement, and side of surgery. RESULTS MFA and F alpha significantly increased over both hemispheres. After alignment on F alpha, a decrease of spectral band power was seen below F alpha, and a band power increase above F alpha. The group of patients with a contralateral ICA occlusion showed significantly more improvement than the group without. The group of patients with neurological deficits showed a tendency for improvement. No differences were found concerning shunt requirement or the side of surgery. CONCLUSIONS After CEA the alpha rhythm frequency increases. In general, patients with a contralateral ICA occlusion improve more than other patients, in agreement with data from the literature on cerebral circulation and brain function.