Class #8 Flashcards
What protects the brain from external forces?
- rigidity of the skull
- cushioning of the cerebrospinal fluid
What is the difference between Focal cerebral Ischemia and Global Ischemia?
FOCAL–> short term low blood flow caused by a stroke, thrombus or embolism that cause cerebral artery occlusion
GLOBAL–> loss of consciousness in cardiac arrest where the blood flow is inadequate to meet the metabolic needs of the entire brain. This causes the inappropriate release of excitatory amino acid neurotransmitters, disrupted CALCIUM balance, free radical formation, and mitochondrial injury, which causes ATP malfunction, and power failure in the brain.
Whats the difference between hypoxia and ischemia?
hypoxia is deprivation of oxygen with maintained blood flow
ischemia occurs when there is interrupted or reduced blood flow and glucose, and a disturbance in the removal of metabolic wastes
What conditions may cause hypoxia?
- reduced atmospheric pressure
- carbon monoxide poisoning
- severe anemia
What is the zone of penumbra?
ischemic but still viable cerebral tissue that lays between the location where the infarction is occurring and healthy, normally perfused tissue
What 4 things occur as a result of global ischemia?
- release of excitatory amino acid neurotransmitters
- disruption of CALCIUM balance
- free radical formation
- mitochondrial injury, causing ATP malfunction and power failure
Where does cell death occur the earliest after global ischemia?
- Purkinje cells of the cerebellum
- Neurons in the Sommer sector of the hippocampus
What are “watershed” areas?
Areas if the brain located at the border zones between overlapping territories supplied by the major cerebral arteries that are extremely susceptible to ischemia., resulting in focal defects
What is laminar necrosis?
Short segments of necrosis that occur within and parallel to the cerebral cortex
How is global cerebral ischemia treated?
depends on the underlying cause, but the goal is to increase oxygen supply to the troubled area of the brain why decreasing the metabolic needs of the brain during the non-flow state.
- ventilation
- supplemental O2
- glycemic management
In global cerebral ischemia, neuron injury causes the release and activation of mediators that overstimulate cell receptors. Why is this a problem? (hint:glutamate)
The most common amino acid is glutamate, which attaches to and opens calcium channels, causing excess amounts of CALCIUM to leak into the cells. This causes:
- protein breakdown
- free radical formation
- DNA fragmentation
- Mitochondrial injury
- Cell death
Explain the difference between Vasogenic Cerebral Edema and Cytotoxic Cerebral Edema
both result in INCREASE intracranial pressure
VASOGENIC
-occurs when the integrity of the blood-brain barrier is disrupted allowing water and proteins to escape into the extracellular fluid (interstitial space) that surrounds brain cells
CYTOTOXIC
-occurs when there is actual swelling of the brain cells themselves due to increased intracellular fluid
What causes Vasogenic edema? And what does it cause?
hemorrhage, meningitis, injury, tumors
Causes: herniation, focal defects, increased intracranial pressure, and altered LOC
What causes cytotoxic edema? And what does it cause?
water intoxication, impaired Na+/K+ pump
Causes: cell rupture, damage to surrounding tissue, and increased intracranial pressure
Explain the Monro-Kellie hypothesis
The cranial cavity contains about 10% blood, 10% cerebrospinal fluid, and 80% brain tissue. It maintains a set intracranial pressure because an increase in one of the 3 components causes a decrease in another, maintaining proper, safe pressure.
What causes an increase in the tissue component of the intracranial space?
tumor
edema
bleed
What causes an increase in the blood component of the intracranial space?
vasodilation, outflow obstruction
What causes an increase in the CSF component of the intracranial space?
increased production
decreased absorption
obstruction
Explain the pathophysiology of increased intracranial pressure
- compartment syndrome in the skull
- intracranial pressure is greater than arterial blood pressure
- arteries collapse, blood flow to the brain is cut off
What is the formula for “compliance”?
C= change in volume
~~~~~~~~~~~~~~~~
change in pressure
Which component of intracranial volume is most restricted in its ability to compensate/undergo change?
tissue volume. CSF and blood volume are best able to compensate for changes in ICP
Why is hyperventilation sometimes used as a treatment method for increased ICP?
elevated PCO2 in the blood cause compensatory vasodilation of the cerebral blood vessels. Vasodilation would allow the influx of more blood to the brain, thus increasing the ICP even more. A decrease in PCO2 causes vasoconstriction, which will decrease the influx of more fluid to the area, and increase MAP and CPP. This is why hyperventilation (decrease in PCO2) is sometimes used in the treatment of ICP.
Explain the 3 stages of intracranial pressure
STAGE 1
-minimal increase in ICP d/t compensatory mechanisms are known as intracranial HTN
STAGE 2
-any change in volume greater than 100-120 mL means a DRASTIC increase in ICP
STAGE 3
- sustained increase in ICP. ICP approaches the MAP, which causes cerebral perfusion to decrease (hypoxia)
What is the body’s natural response to a decrease in cerebral perfusion?
raise systemic blood pressure and dilate Cerebral blood vessels, increasing cerebral blood volume, which contributes to further increase in ICP lowering perfusion pressure.
How will my patient with increased intracranial pressure present?
- Decreased LOC
- headache/vomiting
- papilledema, pupillary changes
- posturing (decerebrate, decorticate)
- decreased motor function
What are the LATE signs of intracranial pressure? How is this treated?
CUSHING REFLEX
- HTN (widened pulse pressure)
- reflex bradycardia
- altered respirations
decrease CO2 levels
Explain brain herniation.
increased intracranial pressure pushes the brain out of position, which causes brain tissue to be compressed either into the center of the brain, against bone, or against the golds of the dura mater
What is an early sign of brain herniation?
compression of the oculomotor nerve
I might think my infant is experiencing increased intracranial pressure when he/she exhibits these signs/symptoms:
- bulging fontanelles
- cranial suture separation
- increased head circumference
- high pitched cry
What is hydrocephalus?
When an increase in cerebrospinal fluid enlarges ventricles and compresses brain tissue
What is the difference between non-communicating/obstructive hydrocephalus and communicating hydrocephalus
non-communicating/obstructive occurs as a result of CSF blockage by congenital malformations, tumours, inflammation, or hemorrhage.
Communicating occurs as a result of impaired reabsorption of CSD via arachnoid villi d/t infection, scarring, blockage by lysed RBCs post repair of bleed
How might someone with hydrocephalus present?
- fontanel bulging in fetus/newborn
- signs of increased ICP in all ages
- optic nerve atrophy/blindness
What’s the difference between primary and secondary traumatic brain injuries?
primary injuries occur due to direct impact from diffuse axonal injury or contusions
secondary injuries occur due to ischemia, hemorrhage, infection and increased ICP
If my patient has experienced primary impact to the head, what kind of traumatic brain injury is this?
coup contusion
What is a contrecoup contusion
a traumatic brain injury as a result of secondary impact to the head
How do you explain the difference between a mild, moderate and severe traumatic brain injury?
MILD occurs with concussion, exhibiting limited symptoms or mild changes in LOC
MODERATE occurs with small hemorrhage/edema, causing cognitive/motor deficits, hemiparesis and nerve palsies
SEVERE occurs with shearing pressure/tissue damage causing hemiplegia, elevated ICP or coma
What is post concussion syndrome?
memory issues, poor concentration, amnesia lasting months
When does an epidural hematoma occur? How would this patient present?
It occurs when there is a tear in the meningeal artery.
This patient would exhibit rapid bleeding, unconsciousness followed by a brief lucid period.
-uncal herniation causing:
-ipsilateral pupil dilation &
contralateral hemiparesis
- GOOD PROGNOSIS IF TREATED BEFORE LOSS OF CONSCIOUSNESS
Explain a subdural hematoma
venous tear between dura and arachnoid mater, causing slower bleeding
ACUTE
-increased ICP, decerebrate posturing, loss of consciousness, high mortality
SUBACUTE
-some improvement, then rapid deterioration
CHRONIC
-slow bleed, decreased LOC, drowsy, confused, HEADACHE