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Unit 2 - Brain Ischemia (Intracranial Pressure
Normal: 0-15 mmHg
3…
Unit 2 - Brain Ischemia
Brain Layers
- Skin
- Muscle
- Periosteum
- Bone
- Dura mater
- Epidural space
- Subdural space
- Arachnoid
- Subarachnoid space
- Pia mater
Cerebral Arteries
- Common carotid artery --> External & Internal carotid artery
- 2 internal carotid arteries supply anterior
- Vertebral arteries supply posterior
- IC + VA = Circle of Willis
- Provides blood to whole brain
- Anterior cerebral artery (supplies medial)
- Middle cerebral artery (supplies lateral)
- Posterior cerebral artery (supplies occipital lobe)
Cerebral Edema
- Increase in fluid d/t fluid accumulation
Vasogenic Edema (around brain)
- Fluid build-up around brain
- Tumours, prolonged ischemia, hemorrhage, infection
- Blood-brain barrier impaired
- Water and protein escape from vascular space to extracellular space
Cytotoxic Edema
- Brain cells swelling (resulting in apoptosis)
Severe ischemia --> less blood flow --> cell membrane ruptures --> damaging neraby cells --> increased brain fluid
Intracranial Pressure
- Normal: 0-15 mmHg
- 3 factors: Brain tissue, CSF, Blood
Monro-Kellie Hypothesis
Compensatory responses to change in volume (more CSF/blood = reduced blood flow, and vice-versa)
*Small ICP changes (2-3 mmHg) are tolerated
-
Etiology
- Intracranial hemorrhage
- Hemorrhagic stroke
- Ruptured aneurysm
- Traumatic brain injury
- Ischemic CVA
- Infections
- Neoplasm (tumour in respiratory tract)
- Vascular anomalies
Clinical Manifestations
- Headache
- LOC decrease (early symptom)
- Papilledema (optic disc swelling, dilated pupils)
- Impaired pupil responsiveness to light
- Systolic hypertension - widened pulse pressure
- Bradycardia
- Paralysis/unable to move
- Altered respiratory patterns
- Unresponsiveness to stimulation
- Unable to move, verbalize, or open eyes
Cerebral Blood Flow
- Cerebral perfusion pressure (CPP) is pressure of blood to brain
- CPP = MAP (mean arterial pressure) - ICP
- Maintain at 70-100 mmHg
50 mmHg = risk of brain death
Balance between adequate oxygen and ICP
-
Cerebrovascular Accident (CVA)
- Sudden onset of neurological dysfunction d/t abnormal cerebral circulation --> brain infarction (brain cell death)
Risk Factors
- Age/Gender
- Family history
- Race
- Hypertension (!)
- High cholesterol
- Smoking
- Diabetes
- Heart/blood diseases
- Alcohol/drugs
- Sedentary lifestyle
1. Ischemic Stroke
- Reduced/interrupted blood flow
- Most common (70-80%)
- Thrombosis/embolism
Thrombus: Blood clot
- D/t changes in endothelium of vessels (atherosclerosis, aging, hardening), blood flow, or blood consistency
Embolism: Traveled blood clot
- Often stuck at bifurcations like cartoids or middle cerebral artery
- Foreign bodies (gas/air)
- Fat tissue
- Small blood piece
2. Hemorrhagic CVA
- Rupture of vessel
- Sudden, often fatal
- Blood floods into brain tissue
- Compression & displacement --> local ischemia
- Cerebral edema --> Increased ICP
- Toxic effects of blood
Etiology
- Cerebral aneurysm (from trauma, drugs, uncontrolled HTN, etc,)
Clinical Manifestations
- Vomiting
- "Worst headache in my life"
- Cerebral edema
- Increased ICP
Subarachnoid Hemorrhage
- Cerebral aneurysm rupture --> bleeding into subarachnoid space
- D/t injury, clotting disorders, blood thinners, etc.
Complications
- Re-bleeding (most common)
- 3-10 days after
- Need to maintain CPP
Stroke Classification/Terms
- Penumbra
- Minimally perfused cells around core of CVA
- Goal is to restore circulation to area
- Trans-Ischemic Attack (TIA, mini-stroke)
- Temporary reduction in blood flow
- Reverses before infarction
- Neurological deficits completely restored within 24 hours
- Warning sign of future CVA
Clinical Manifestations
- Motor deficits
- Affects contralateral side (hemiparesis)
- Hemineglect
- Language deficits
- Dysarthria (weak muscle control --> slurred speech)
- Aphasia (can't speak/understand)
- Dysphasia (less severe aphasia)
- Cognitive deficits
- Impaired concentration, memory, judgement, behaviour, reasoning
Traumatic Brain Injury
- External mechanical force causing structural damage
- Prevalent in children/youth, and >60 years
*Non-penetrating vs. Penetrating
Primary Injury
- From initial trauma
- Focal, polar, diffuse injuries
Polar Injuries
- Acceleration-deceleration movement
- Double injury
Diffuse Injury
- From movement of brain within skull
- Widespread axonal damage
Focal Injuries
- Localized to site of impact
- Symptoms dependent on area of damage
- Hemiparesis
- Frontal cortex/temporal lobe --> behavioural, emotional issues
Clinical Manifestations
- Dependent on region of injury
- Headache
- N/V
- Lack of motor coordination
- Dizziness, bad balance, blurry vision, ringing in ears, fatigue
- Behavioural change
- Loss of consciousness
- Present in moderate and severe TBI
Focal Hematomas
Epidural Hematoma
- Arterial bleeding between skull and dura
- Common with skull injury
- Brief loss of consciousness --> lucid period --> rapid progression to unconsciousness
Subdural Hematoma
- Venous bleeding between dura & arachnoid mater
- Symptoms of chronic hematoma develop after weeks in older adults
- Brain shrinks = subarachnoid space increases
Intracerebral Hematomas
- Develops within brain
- Common frontal or temporal lobes
Secondary Injury
- Body response to initial injury after 48-72 hours of TBI
- May be more harmful than initial injury
- May lead to --> Increased ICP, cerebral edema, etc.
- Ruptured vessels may re-bleed, clogged CSF drainage