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25 Cards in this Set
- Front
- Back
key concept about CPP
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its the difference between MAP and ICP (or CVP, whichever is higher)
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key concept regarding the cerebral autoregulatiuon curve in patients with chronic arterial hypertension
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its shifted to the right
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key concept regarding the most important extrinsic influences on CBF
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the most inportant influences are respiratory gas tensions, especially CO2
CBF is directly proportional to PaCO2 between 20-80 mmHg blood flow changes about 1-2 mL/100g/min per mmHg change in PaCO2 |
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key concept about CBF and temperature
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CBF changes 5-7% per 1C change in temp
hypothermia decreases both CBF and CMRO2, pyrexia has the reverse effect |
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key concept about movement of things across the BBB
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movement of any substance across is simultaneously governed by size, charge, lipid solubility, and degree of protein binding in blood
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key concept about things that disrupt the BBB
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its disrupted by severe hypertension, tumors, trauma, strokes, infection, marked hypercapnea, hypoxia, and sustained seizure activity
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key concept about the cranial vault contents
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its a rigid structure with a fixed total volume consisting of brain (80%), blood (12%), and CSF (8%)
an increase in any 1 component must be offset by an equivalent decrease in another to prevent a rise in ICP |
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key concept about IV anesthetics and CBF and CMRO2
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with the exception of ketamine, all IV agents either have little effect on or reduce CMRO2 and CBF
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key concept about CBF and vasopressors
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if there is normal autoregulation and an intact BBB, vasopressors increase CBF only when MAP is below 50-60 mmHg or above 150-160 mmHg
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key concept about the brain and ischemic injury
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the brain is very vulnerable to ischemic injury because of its high oxygen consumption and near total dependence on aerobic glucose metabolism
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key concept about the most effective way to protect the brain during focal or global ischemia
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its hypothermia
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how much of total body oxygen does the brain normally consume?
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20%
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what is the majority of cerebral oxygen consumption used to do?
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60% of it is used to generate ATP to support neuronal electrical activity
*******Fig 26-1***** |
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normal cerebral metabolic rate
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usually expressed in terms of oxygen consumption, CMRO2
normal is 3-3.8 mL/ 100g/min (50 mL/min) in adults |
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where is CMRO2 greatest in the brain?
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in the gray matter of the cerebral cortex
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what does CMRO2 generally parallel?
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cortical electrical activity
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what happens when oxygen supply is cut off to the brain?
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since the brain has high oxygen consumption and does not have much oxygen reserves, unconsciousness occurs within 10 sec as O2 tension falls below 30 mmHg
if blood flow is not reestablished within 3-8 min, ATP stores are depleted and there is irreversible cellular injury |
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what parts of the brain appear to be most sensitive to hypoxic injury?
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the hippocampus and cerebellum
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what is the primary energy source for neuronal cells?
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glucose
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normal brain glucose consumption
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its 5 mg/ 100g/min
90% is metabolized aerobically |
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what does CMRO2 therefore normally parallel?
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glucose consumption
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when is this relationship not maintained?
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during starvation
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what happens during starvation?
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ketone bodies (acetoacetate and B-hydroxybutyrate) become major energy substrates
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can the brain use lactate?
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it can take up and metabolize lactate, but cerebral function normally depends on a continuous supply of glucose
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effect of hypo and hyperglycemia on the brain
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acute sustained hypoglycemia is injurious to the brain
hyperglycemia is bad also, however, as it can accelerate cerebral acidosis and injury, worsening global and focal hypoxic brain injury (this is why theres controversy over how closely to maintain blood glucose, as tight control can prevent this hyperglycemia, but can lead to iatrogenic hypoglycemia) |