Anoxia
Terms
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- Definition of anoxia
- complete or partial disruption of oxygen supply to tissue
- Most common cause of anoxia
- cardiac arrest
- Other causes of anoxia or hypoxic encephalopathy
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-reduced arterial pressure secondary to lung disease
-reduced hemoglobin to carry oxygen secondary to anemia or blood loss
- biochem block of cerebral utillisation of oxygen secondary to cyanide poisoning - Mitigators of extent of hypoxic damage
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-duration
-body temperature (hypothermia is protective) - Specific neuroanatomy damaged by anoxia
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In order of effect
-hippocampus (loring)
-hippocampus/frontal cortex (lindsay & bone)
-parietal/occipital cortex
-basal ganglia/cerebellum
-brain stem
General guideline is grey more than white, and most vulnerable are watershed regions at end of vascular supply : hipposcampus, basal ganglia, cerebellum, occipital cortex, frontal regions - Progression of deficits over time intervals
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-inattention
visual disturbance
-incoordination
-amnesia
-loss of consciousness
-brain stem signs
-flexion or extension to pain/death - Damage to hippocampus in anoxia results in
- anterograde amnesia
- Visuspatial deficits secondary to anoxia include
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central vision disturbances
visual agnosia
cortical blindness - Effects of oxygen deprivation on cognitive performance by partial pressure of arteria oxygen (PaO2)
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- 75% of normal - complex task performance altered
- 65% normal - memory is impaired
- 50% of normal - judgment altered and unconsciousness may occur
- 30-40% of normal death results - Mechanism of neural damage in anoxia/hypoxia
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1. Lactic acidosis
2. Calcium influx and intracellular accumulation of calcium due to ionic pump failure
3. Neurotoxicity of excitatory amino acide NT - glutamate
4. formation of oxygen-free radicals following reperfusion/reoxygenation of damaged neuronal membranes