My sister has been diagnosed with fibromuscular dysplasia. Her left carotid artery is completely occluded by a blood clot. The right artery is occluded approximately 68%. She has been having TIA s with numbness and vision loss on one side. Recently she had feeling of her leg weighing 100 lbs and almost felt like it was dragging. She is about to see a vascular surgeon, and her primary care doctor said an ultrasound will probably be performed and if necessary carotid bypass surgery. What are her risks with having this surgery?