chapter 44 prt 2

Stroke (Cerebrovascular Diseases)

• Cerebrovascular diseases can lead to cerebral perfusion problems.
  • Transient Ischemic Attack (TIA).
  • Stroke:
    • Ischemic.
    • Hemorrhagic.

Importance of Learning About Stroke

• Third leading cause of mortality in the United States.
• Causes long-term care and rehabilitation, leading to significant community expenses.
• Risk factors are similar to those for atherosclerotic diseases.
  • High blood pressure.
  • Diabetes.
  • High cholesterol.
  • Smoking.
  • Age.
  • Family history.

Definition of Stroke

• Sudden onset of neurological dysfunction due to brain tissue infarction.
• Blood vessels to the brain are blocked by:
  • Atherosclerosis.
  • Thrombosis.
  • Embolus.
• Brain tissue can only survive a few minutes without oxygen.
  • Leads to neurological deficits.

Thrombotic Strokes

• Associated with atherosclerosis and coagulopathies.
• Atherosclerosis can cause bruit in the carotid arteries.
  • Common carotid divides into external and internal carotid arteries.
  • Internal carotid supplies blood to the brain.
• Bruit:
  • Sound created by turbulent blood flow due to atherosclerosis.
  • Detected with a stethoscope or ultrasound.
• Patients at risk for stroke are often referred for ultrasound to assess carotid artery blockage.
  • If carotid is obstructed by more than 70%, there is a very high risk of stroke.

Embolus

• Usually associated with cardiac dysfunction.
• Thrombus formation in the left atrium (especially with atrial fibrillation) or mural thrombus can dislodge.
• Mural thrombus: thrombus attached to the wall of the heart.
• Dislodged thrombus can travel to the carotid arteries and cause an embolus.
• Neurons survive only 1-2 minutes without oxygen, leading to ischemia, damage, and necrosis.

Ischemia and Penumbra

• When an artery is blocked, the area it supplies undergoes necrosis.
• Tissue around the necrotic region is at risk of ischemia but is more viable, called the penumbra.
• Goal: restore perfusion to save the penumbra.
• Window for thrombolytic treatment: three hours.
  • If treatment is given within three hours, the penumbra can be saved.
  • After three hours, the penumbra also undergoes necrosis.

Clinical Manifestations of Stroke

• Contralateral hemiplegia.
  • Damage to one hemisphere causes symptoms on the opposite side of the body.
• Contralateral hemisensory loss.
• Visual field blindness.

Treatment for Stroke

• Salvage the penumbra within a three-hour window using thrombolytics.

Transient Ischemic Attack (TIA)

• Neurological deficits (e.g., speech difficulty, arm weakness) that resolve completely within 24 hours.
• Caused by the body's own fibrinolysis process dissolving the clot and reestablishing blood perfusion.
• Important to admit and investigate patients with suspected TIA, even if symptoms resolve, to prevent subsequent stroke.
• Treatment: Daily aspirin to prevent platelet aggregation.
  • Prophylactic measure.
• If carotid blockage exceeds 70%, carotid endarterectomy or angioplasty is performed.

Hemorrhagic Stroke

• Ischemic strokes make up over 90% of cases; hemorrhagic strokes account for 10% or less.
• Always refer patients for CT scan or MRI to differentiate between ischemic and hemorrhagic stroke.
  • Thrombolytic treatment for a hemorrhagic stroke can be fatal, as it can enlarge the hemorrhage.
• Hemorrhagic stroke: bleeding within the brain parenchyma, often due to hypertension.
  • Small blood vessels in the brain can rupture due to high blood pressure.
• Occurs mostly in basal ganglia or thalamus.
• Subarachnoid hemorrhage: associated with aneurysms and arteriovenous malformations (AVM).

Secondary Injury in Hemorrhagic Stroke

• Bleeding inside the brain parenchyma is the primary injury, but secondary injury is more dangerous.
• Secondary injury: high intracranial pressure (ICP).
  • High ICP can cause the midbrain structure to shift or herniate, leading to death.

Treatment of Hemorrhagic Stroke

• First, stabilize the patient's cardiovascular system (blood pressure, pulse, respiration) before addressing the stroke.
• Perform a CT scan to determine the type and location of the stroke.
• Ischemic stroke: Thrombolytics, anticoagulants, angioplasty, or endarterectomy to prevent worsening neurological deficits.
• Hemorrhagic stroke: Blood pressure management.
  • Avoid aggressive antihypertensive treatment, which can cause a sudden drop in blood pressure and lead to ischemia, worsening the stroke.
  • Even if the blood pressure may seem high, severely dropping it can reduce perfusion to the brain tissue, causing an ischemic stroke on top of the hemorrhagic stroke.

Sequelae of Stroke

• Motoric and sensory deficits.

Motoric Deficits

• Initially, flaccidity or paralysis (most likely paralysis in over 95% of cases).
• Flaccidity: muscle lacks normal tone; if the limb is flexed and released, it immediately returns to its original position.
• Recovery: patients often develop spasticity, with excessive muscle contraction.
• Counsel patients that physical therapy and exercises need to start in the acute phase, because spasticity can cause contractility of the muscles over time (frozen muscle).

Sensory Disturbances

• Contralateral sensory deficit, causing neglect or visual impairment.
• Neglect: patient is unaware of the paralyzed side; for instance, the patient can sense only the left side.
• Visual impairment: homonymous hemianopsia (blindness in the same side of the retina).

Other Risks

• Risk of falls due to paralysis.
• Need to assess risk falls.

Language Deficit

• Broca's area: motoric speech (expression).
  • Expressive aphasia: patient knows the answer but cannot express it (e.g., difficulty speaking).
• Wernicke's area: understanding of speech.
  • Receptive aphasia: patient can express themselves but does not understand or make sense of what is being asked.

Cognitive Deficit

• Deficits in spatial relationships, short-term memory, poor judgment, and concentration.

Cerebral Aneurysm and AVM

• Structural abnormalities that can predispose patients to intracerebral bleeding or hemorrhage.
• Common cause of subarachnoid hemorrhage.

Aneurysm

• Weak point in the blood vessel wall (ballooning of the blood vessels).
  • The wall consists of three layers: intima, media (tonica media), and adventitia (or serosa).
  • If there is a weak point, high blood pressure hits the blood all the time, making it crack and enlarge.
• Risk factors: high blood pressure, acute alcohol intoxication, drug abuse (especially cocaine).
• Pathogenesis: berry aneurysm in the circle of Willis, where the medial layer is very thin.
• Congenital defects can also be a contributing factor.
• Most common location: anterior communicating artery in the circle of Willis.

Clinical Manifestations of Aneurysm

• Meningismus: symptoms similar to meningitis (malaise, fever, headache, stiff neck).
• Photophobia (sensitivity to light).
• Diagnostic tools: MRI and CT scan.
• Treatment: surgical stabilization (clip and repair or embolization).

Post-Aneurysm Bleeding Management

• Vasospasm, which occurs 2-10 days after the bleeding: secondary to aneurysm.
• Management: maintain blood volume and blood pressure at normal to slightly high levels.
• Use calcium channel blockers for vasospasm.

Arteriovenous Malformation (AVM)

• Disease of young people (10-30 years of age).
• Normal blood flow:
  • Arterial (pressure 35-40 mmHg) → Capillary (pressure 20-25 mmHg, exchange of nutrients and oxygen) → Venule (pressure 5-10 mmHg).
• AVM: direct connection between arterial and venule without a capillary bed.
• Problems:
  • No exchange of nutrients and oxygen (neurological deficits).
  • High pressure (35-40 mmHg) directly impacts the thin-walled venule; eventually, the venule enlarges and ruptures, leading to bleeding.
• Clinical manifestations: seizure and neurological dysfunction.
• Treatment: surgical removal or radiosurgery.

CNS Infection

• Brain blood barrier (BBB) prevents bacterial organisms and foreign objects from entering the brain.
• Infection can reach the CNS through bloodstream, skull fracture, or cranial nerves.
• In gestation, can come through maternal-fetal exchange.
• Risk factors: immune-compromised patients, poor nutrition, and steroid therapy (steroids suppress the immune system).
• Meningitis and cerebral abscess (bacterial infection), encephalitis (viral infection).

Meningitis

• Bacteria reach CNS through bloodstream or sinuses/ear infection.
• Most common bacteria: Streptococcus pneumoniae in adults, Neisseria meningitidis in young people.
• Bacteria attack the leptomeninges (dura mater, arachnoid, and pia mater), causing inflammation and inflammatory exudate.
  • Can lead to hydrocephalus.
• Classic presentation: headache, fever, stiff neck (meningismus), confusion, and delirium.
• Diagnosis: lumbar puncture (LP) and CSF analysis/microscopy.
• Treatment: IV antibiotics and possibly steroids (controversial) to prevent hydrocephalus progression.
• Prevention: vaccination for Neisseria meningitidis and Haemophilus influenzae type b (Hib).