Noninvasive assessment of cerebral circulation before, during and after carotid surgery

Abstract

Non-invasive ultrasound investigations were evaluated in patients with carotid artery stenosis in comparison with radiological disease gradations and perioperative blood pressure measurements. The aim was to assess cerebrovascular hemodynamics before, during and after carotid thrombendarterectomy (CEA) in relation to the clinical outcome of the surgical intervention.Intracranial collateral blood flow as a consequence of high grade carotid artery disease can be investigated by means of blood flow velocity measurements with 3D-transcranial Doppler flow mapping and proximal common carotid artery compressions. The value and risks of common carotid artery compression were therefore assessed. No adverse effects were seen in 3383 patient studies retrospectively reviewed. In addition, we found that transcranial Doppler without carotid compression may lead to false identification of the posterior cerebral artery.Preoperative blood flow velocities within the carotid stenosis and poststenotic blood pressures during intraoperative carotid clamping were analysed with respect to some serious postoperative complications. We found that blood flow velocities within severe internal carotid artery (ICA) stenoses are inversely related to the poststenotic collateral blood pressure. High diastolic blood flow velocities within the ICA stenosis might indicate low collateral blood pressures and increased risk for severe postoperative neurological complications. The discrepancies occasionally seen between preoperative ultrasound investigation and angiography might therefore be explained by high collateral backpressures, which may induce unusually low blood flow velocities within severe ICA diameter reductions.The carotid compression test, performed during the preoperative transcranial Doppler investigation, was used to predict middle cerebral artery (MCA) blood flow reductions during intraoperative carotid artery cross-clamping. Surprisingly, we found a greater decrease of the MCA blood flow velocities during the carotid compression test compared with the flow changes during cross-clamping. Signs of cerebrovascular autoregulation due to carotid compression were not reproducible during carotid clamping under general anaesthesia. The few patients with postoperative adverse reactions happened to show a pattern of low collateral blood pressures and relatively high MCA blood flow velocities during cross-clamping. Since general anaesthesia affects cerebral autoregulation we performed a postoperative transcranial Doppler study to assess the MCA blood flow pattern after surgical restoration of normal ICA blood flow. In the majority of the patients, we observed increased blood flow velocities bilaterally within the MCA, which might be a result of postoperative hyperperfusion or autonomic imbalance of carotid sinus baroreceptors.In conclusion, evaluations of cerebrovascular hemodynamics in CEA patients might give important information indicating risks of complications.