Hemodynamics of carotid back pressure and cerebral flow during endarterectomy

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.

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.

Technique and clinical results of carotid stump back-pressure to determine selective shunting during carotid endarterectomy

A method of confirming carotid back pressure accuracy, variability during carotid clamping, and the clinical results with a modified back pressure shunt criterion were evaluated in 665 carotid endarterectomies. Mean arterial pressure, back pressure, and internal jugular vein pressure were measured. Cerebral perfusion pressure (back pressure-jugular vein pressure) and the collateral to hemisphere vascular resistance ratio, (ratio = [arterial pressure-back pressure]/[back pressure-jugular vein pressure]) were calculated. A shunt was used when cerebral perfusion pressure less than 18 mm Hg. Back pressure accuracy was confirmed by test occlusion of the internal carotid artery distal to the plaque. Initial back pressure values were falsely high in 83 (12.5%) carotid endarterectomies. The mean SD (n = 665, mm Hg) were arterial pressure = 84.0 +/- 9.06, back pressure = 41.0 +/- 15.9, jugular vein pressure = 6.2 +/- 3.9, cerebral perfusion pressure = 35.1 +/- 5.7, and resistance ratio = 1.85 +/- 1.44. Perfusion pressure was less than 18 mm Hg in 82 (12.3%), of which 74 (11.1%) were shunted, and 8 (1.2%) had perfusion pressure increased greater than or equal to 18 mm Hg during carotid endarterectomy with phenylephrine. Back pressure was less than 25 mm Hg in 107 (16.1%), less than or equal to 25 in 114 (17.1%), and less than 50 mm Hg in 481 (72.3%). Pressures were continuously monitored during 28 carotid endarterectomies, and all had a positive linear relationship between arterial pressure and back pressure, and minimal variability in the back pressure/arterial pressure and resistance ratios. Only two patients (0.3%) had a new neurologic deficit in the first 12 hours after carotid endarterectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Does intracranial dye study contribute to evaluation of carotid artery disease?

One thousand consecutive cerebral arteriograms for suspected carotid artery disease were retrospectively evaluated for the intracranial disease component. Only 784 patients (78 percent) had arteriograms of the intracranial circulation. Forty-six patients (6 percent) had siphon stenosis in the range of 5 to 70 percent. No patient had a lesion encompassing more than 75 percent of the vessel diameter. Thirteen patients (2 percent) had intracranial aneurysms. All patients were asymptomatic from the standpoint of their aneurysms and none required surgical intervention. One additional patient was noted to have an intracranial tumor, which was confirmed by computerized tomography. In this patient population, intracranial dye study did not provide information that altered management.

Collateral cerebral vascular resistance in patients with significant carotid stenosis

This study tests, the hypothesis that asymptomatic patients with hemodynamically significant internal carotid artery stenosis have a lower ipsilateral collateral cerebral vascular resistance and hence greater blood flow than their symptomatic cohorts. We measured internal carotid artery blood flow and cerebral perfusion pressures intraoperatively prior to and after carotid endarterectomy in 35 symptomatic and 10 asymptomatic patients with hemodynamically significant internal carotid artery stenosis. When the stenosis produced 30% or greater reduction in blood flow the calculated nondimensional normalized ratio of collateral cerebral vascular resistance of ipsilateral hemisphere cerebral vascular resistance was 1.15 +/- 0.83 (mean +/- SD) for the 10 asymptomatic patients and 2.98 +/- 1.89 for the 35 symptomatic patients (p = 0.0044). For the subgroup of 22 patients with 50% or greater reduction in internal carotid artery blood flow the resistance ratios were 0.782 +/- 0.541 for the 5 asymptomatic patients and 3.21 +/- 2.26 for the 17 symptomatic patients (p = 0.029). These results suggest that asymptomatic patients with hemodynamically significant internal carotid artery stenoses have a lower collateral cerebral vascular resistance than their symptomatic cohorts. The low collateral resistance may provide an adequate collateral cerebral blood flow to prevent ischemia and symptoms.