Pathophysiology: An ischemic stroke is when there is a loss of blood circulating to an area of the brain. This can occur because blood flow is blocked by a blood clot.
Lack of blood flow to brain tissue caused by blood clot in cerebral vessels.
- Blood clot in vessel in brain
- No flow past clot
- 87% of all strokes
- Not immediately seen on CT scan (24 hours)
- MRI for better view
- Risk Factors
- Cardiac Dysrhythmias
- Oral Contraceptives
- Substance Abuse
- Presentation dependent on location of clot
- See Stroke Assessment Lesson
Now, let’s talk about ischemic strokes and the major points you need to know.
So Ischemia means low blood flow or low oxygen. Ischemic strokes are caused by a blood clot that blocks vessels within the brain. When that happens, there is no blood flow past that clot, which causes the brain tissue to die. So this is like having a rock plugging up your garden hose – you can’t water your flowers that way. It only takes 10 minutes without flow for brain cells to die completely. Ischemic strokes represent 87% of all strokes in the U.S. So when a patient presents to the Emergency Department with a stroke, one of the first things we do is to get a CT scan. But, ischemic strokes may not be seen right away on a CT scan. They begin to show up at about 6 hours and are obvious on a CT scan within 24 hours. You can see this scan shows this darker area here is showing that this tissue has no blood flow to it and it is dying. If we suspect damage, but can’t see detail on the CT scan, we’ll get an MRI for a better image.
Common risk factors for stroke are hypertension, diabetes, obesity, and atherosclerosis. Now, what do these disorders all have in common? They are all vascular issues or cause vascular damage. Just like we talked about in the cardiac course – any damage to the vessels can cause plaque to build up and clots to form, like the one you see here. Patients with cardiac dysrhythmias like atrial fibrillation are also at risk for clots, as well as women taking birth control and people who abuse illicit drugs, especially cocaine. These clots can form in the brain or they could form elsewhere and travel to the brain.
We’ll talk about this in more detail when we get to the assessments lesson, but we want you to be aware that the specific presentation will be different for every patient depending on where the clot is in their brain. We have a great cheatsheet on this, so make sure you check it out. But this structure here is called the Circle of Willis – it’s the main structure feeding all of the arteries in the brain. If you get a clot somewhere in this circle, you will lose a significant amount of blood flow. What you see here is as if there was a clot in the Middle Cerebral Artery here. You can see on the patient’s left side that it’s getting a little hazy and a little darker and less defined. This shows the beginnings of a Left MCA stroke. The CT scan from the first slide was actually a severe Right MCA stroke – so you can see how if it goes on for too long, it causes more and more damage. We’ll look in the therapeutic management lesson about what we do to stop it.
So remember that an ischemic stroke is a lack of blood flow to the brain caused by a blood clot in the cerebral vessels. The risk factors for stroke are anything that affects the integrity of the vessels or causes blood clots anywhere in the body. The specific symptoms and presentation will depend entirely on WHERE the clot is in the brain. Make sure you check out the cheatsheet and the assessment lesson to learn more!
So that’s the basics about ischemic stroke. Make sure you check out the rest of this module to learn more about how we manage patients with strokes. Happy nursing!