Week 12: Stroke Flashcards
Differentiate between cerebral hypoxia and cerebral ischemia
Cerebral Hypoxia: is a result of low oxygen in the blood; while the perfusion and flow remain uninterrupted, there is insufficient blood supply to the brain
Cerebral Ischemia: is low oxygen in this tissues and is a result of impaired blood flow to the brain; oxygen in the blood is normal or unaltered, however, flow is obstructed.
In both cases, neurons will die as a result of lack of oxygen. Neuronal die-off is initiated by a series of chemical reactions known as an ischemic cascade.
Describe the molecular mechanisms of neuronal injury in stroke
An injured brain reacts with (1) structural, (2) chemical, and (3) pathophysiologic changes where the primary injury (original trauma) results in a secondary injury that is a consequence of alterations in cerebral blood flow and increased intracranial pressure (ICP) and O2 delivery.
Differentiate the pathogenesis of ischemic and hemorrhagic stroke
nIschemic strokes make up 80% of all cases of stroke and involve obstruction of blow flow to cerebral arteries, obstruction may be caused by thrombi or emboli or atherosclerosis, or a combination. Ischemic stroke includes:
* thrombotic stroke
* embolic stroke - typically resulting from atrial fibrillation
* lacunar stroke - lacunar infarcts or small vessel disease
* hemodynamic stroke - brain hypoperfusion
Ischemic stroke is the result of cellular injury that triggers the inflammatory response. 6-12 hours after occlusion, the affected area becomes pale and softens. Necrosis and swelling begin to develop 48-72 hours later. After two weeks, the necrosis resolves but a cavity remains surrounded by glial scarring. Vascular remodeling will occur (angiogenesis) to promote collateral circulation but will not be the same as previous vessels.
Hemorrhagic stroke makes up to 20% of all cases of stroke and results from bleeding in the brain due to a variety of factors that may include hypertension, tumors, coagulation disorders, trauma, or illicit drug use (particularly cocaine). Hemorrhagic stroke is also known as spontaneous intracranial hemorrhage. May manifest in focal neurologic deficits, altered consciousness, headache (sudden, severe).
Note: tumors are extremely vascular and make their own blood supply through the generation of vessels - if tumor vasculature ruptures, it will bleed into the brain.
Describe risk factors for stroke
Risk factors for stroke include:
* poorly controlled or uncontrolled HTN
* smoking (increases risk by 50%)
* insulin resistance and diabetes
* polycythemia (increased RBCs), thrombocythemia (increased platelets), sickle cell
* high total cholesterol, low HDL, elevated lipoprotein(a)
* obesity
* physical inactivity
* congestive heart disease, peripheral vascular disease
* arterial fibrillation
* family history and genetics
* sleep apnea
* depression
* chlamydia pneumoniae infection
* post-menopausal hormone therapy
* high sodium intake, low potassium intake
* hyperhomocysteinemia
Describe the manifestations that occur with an evolving stroke
Manifestations will depends on the distribution of the artery obstructed , different sites of obstruction create different occlusion symptoms.
If the cortex or medulla are impacted contralateral sensory and motor manifestations occur because the motor tracts originate in the cortex and most cross over the medulla (both sides of the body)
Ipsilateral manifestations (one sided) occurs on same side for tracts that do not cross over
Stroke can be identified using the FAST acronym:
Face - is it drooping?
Arms - can you raise both?
Speech - is it slurred or jumbled?
Time - to call 9-1-1 right away!
Discuss the diagnostics and timeliness of treatment for stroke
Clients presenting to the ED with suspected or acute stroke or TIA must have an IMMEDIATE clinical evaluation & investigations to establish a diagnosis and determine eligibility for thrombolytic therapy and endovascular thrombectomy treatment (EVT). We need to determine ASAP if the stroke is ISCHEMIC or HEMORRHAGIC because treatment is NOT the same! We need to (1) restore perfusion ASAP, (2) counteract the ischemic cascade pathways, (3) lower cerebral metabolic demand (decrease the oxygen demand - can do this by cooling the patient down or inducing coma in severe cases), (4) prevent recurrent ischemic events, (5) promote tissue restoration, and (6) treat hypertension with CAUTION!
Note: If we lower blood pressure too much we may decrease perfusion which is NOT ideal!!
Acute Ischemic Stroke:
* Within 24 hours of symptom ONSET (not admission) the patient needs to be screened clinically and have imaging
* Within 4.5 hours of of ONSET we need to determine eligibility for IV thrombolytics (alteplase) and/or endovascular thrombectomy
* Within 6 hours of ONSET we need to determine eligibility for EVT
* Target door-to-needle time of alteplase treatment is less than 60 minutes!!!
* Clients eligible for thrombolytics and EVT can be treated with alteplase while preparing angiography suite for EVT
Explain the reperfusion injury and how it relates to treatment for stroke
Reperfusion is the restoration of blood flow following ischemic stroke, however, it can lead to further injury through multiple pathological processes such as infiltration of inflammatory cells (i.e., leukocytes and platelets) and complement activation where the inflammatory response build and phagocytic cells (now starving from being prevented access!) will eat anything in sight - including viable/still living tissue! Reperfusion may also accelerate oxidative stress.
Identify the classifications of drugs used in the treatment of stroke
Pharmacotherapy for Ischemic Stroke:
* Antiplatelet (ADP receptor blocker) - i.e., clopidogrel: prolongs bleeding time by interfering with aggregation of platelets. They prevent and treat arterial thrombosis by blocking ADP receptors. ADP promotes platelet aggregation by recruiting additional platelets to site of injury, by blocking the receptor we alter the plasma membrane of platelets and they become unable to recognize chemical signals required to aggregate.
* Cyclooxygenase (COX) inhibitors; anti-platelet - i.e., acetylsalicylic acid
* Thrombolytics: tissue plasminogen activator - i.e., alteplase
What is a cerebrovascular disorder?
Cerebrovascular disease is the most frequently occurring neurologic disorder and is any abnormality of the brain caused by a pathologic process in blood vessels. There are two types of brain abnormalities:
1. Ischemia with or without infarction
2. Hemorrhage
Examples include:
- Cerebrovascular accidents (CVAs) - i.e., stroke
- Transient ischemic attacks (TIAs)
- Aneurysms or malformations
What is the difference between focal cerebral ischemia and global cerebral ischemia?
Focal cerebral ischemia is specific to a region or area of the brain not adequately perfused (i.e., stroke), global cerebral ischemia is when blood flow to the entire brain is compromised (i.e., hypovolemia, MI, HF)
What is a cerebral infarction?
Cerebral infarction is when a lack of adequate blood supply to brain cells deprives them of oxygen and vital nutrients, which causes brain cells infarct (die). There are two types of infarction:
1. Ischemic infarcts: caused by vascular occlusion which can result from thrombi or emboli, or atherosclerosis, or potentially a combination.
2. Hemorrhagic infarcts: caused by bleeding that occurs into infarcted area from leaking vessels or reperfusion
Discuss how atrial fibrillation can result in embolic stroke
During atrial fibrillation, the heart is not contracting properly - it does not eject blood fully because it is not fully contracting (more like a quiver). As a result, blood pools in the atrium, forming clots and some of those clots may break up and form emboli. If the emboli is ejected into systemic circulation, it may enter the cerebral circulation and occlude the vessel - causing stroke.
What is a Transient Ischemic Attack (TIA)?
Specifically defined as episodes of neurologic dysfunction lasting no more than 1 hour and resulting from cerebral ischemia. If it looks like a TIA but lasts longer than an hour, by definition it is a stroke and not a TIA. 3-17% of clients experiencing a TIA will have a stroke within 90 days. Manifestations include:
* weakness
* numbness
* sudden confusion
* loss of balance
* loss of vision
* sudden severe headache
What is a thrombotic stroke?
Thrombotic stroke is caused by a cerebral thrombus (clot) which is an arterial occlusion caused by thrombus formation in large or small cerebral arteries. Platelets and fibrin adhere to a damaged wall and form clots that occlude the artery. This process can be attributed to atherosclerosis and inflammatory disease process.
What is an embolic stroke?
Embolic stroke results from fragments that break from a thrombus formed outside of the brain that eventually travel to the brain. They commonly originate in the heart, aorta, and common carotid artery. It involves small blood vessels and obstructs at bifurcations or other points of narrowing, causing ischemia. It frequently occurs in middle cerebral artery (the largest cerebral artery). The source of the emboli continues to exist after stroke, so the chances of a second stroke are high.
