Stroke stops oxygen from reaching the brain and causes brain cells to die immediately. It’s caused by a bleeding or clotting event that interferes with blood flow to the brain. When it comes to treatment, time is critical. Patients also must meet rigorous existing criteria to receive the two treatment options that doctors have in their arsenal: a clot-dissolving drug that must be administered within 3-4½ hours after stroke, and surgery to remove the clot, which can be performed up to 24 hours after the occlusion.