Chapter 24: Hypoxia & Ischemic Brain Injury Flashcards
DEFINITION:
Most typically defined as a complete lack of oxygen in arterial blood, due to a profound and sudden medical event such as cardiac arrest or loss of perfusion pressure
Anoxia
DEFINITION:
A deficient amount of oxygen availability in the blood supply to the brain. It is distinguished from anoxia, but the two are often used interchangeably in the literature and medical reports
Hypoxia
DEFINITION:
Another term commonly used to refer to reduced partial pressure oxygen in arterial blood (<60 mm Hg).
Hypoxemia
Note: Hypoxemia can lead to hypoxia
DEFINITION:
The failure of perfusion of blood through the cerebral vessels to tissue (e.g., lack of blood supply).
Ischemia
Note: Both ischemia and anoxia are usually involved in cases of profound and sudden cardiac arrest
What ACUTE conditions may cause hypoxic-ischemic brain damage?
- Cardiac Arrest
- Acute respiratory distress syndrome (ARDS)
- Carbon monoxide poisoning
- Suffocation, drowning, hanging
- Massive blood loss due to trauma
- Prolonged seizures
- Anesthesia accidents in surgical procedures
What CHRONIC conditions may cause hypoxic-ischemic brain damage?
- Chronic obstructive pulmonary disease (COPD)
- Obstructive sleep apnea (OSA)
- Asthma
- Conditions that paralyze the respiratory system (e.g.,, amyotrophic lateral sclerosis, myasthenia gravis, etc.)
What brain regions show vulnerability to hypoxia/ischemia?
- Neocortex (layers 3, 5, 6)
- Hippocampus (pyramidal cells in CA1)
- Basal ganglia (striatum, globus pallidus)
- Cerebellar regions (Purkinje cells)
- Visual cortex
- Thalamus
DEFINITION:
Apoptosis
Programmed cell death.
Apoptosis is part of normal regulation and turnover of cells, but can also result from pathologic processes such as ischemic.
DEFINITION:
Adenosine Triphosphate
Adenosine Triphosphate (ATP) is a chemical compound that provides energy for cells/neurons.
Note: under anoxic/hypoxic conditions, less ATP becomes available in the neuron, leading it to catabolize itself.
DEFINITION:
Chronic obstructive pulmonary disease (COPD)
A term that encompasses several conditions of pulmonary disease (e.g., emphysema, bronchitis) in which there is progressive obstruction of expiration; COPD can produce chronic hypoxia and, depending on the severity, may result in cognitive impairment.
DEFINITION:
Glutamate
The most common excitatory neurotransmitter in the brain. Under conditions of anoxia/hypoxia, excessive amounts of glutamate are released into the synaptic cleft, and it becomes excitotoxic, as well as contributing to further deleterious processes in the neuron.
DEFINITION:
Ischemic-hypoxic encephalopathy
Refers to the encephalopathy resulting from the combined effects of anoxia/hypoxia and ischemia. In their purest presentations, anoxia/hypoxia and ischemia may produce somewhat different neuropathology, but most cases in which the brain suffers marked disruption of oxygen supply inolve both processes.
DEFINITION:
Necrosis
Refers to the death of tissue or neurons, typically due to insufficient blood supply.
DEFINITION:
Obstructive sleep apnea (OSA)
a disorder that involves recurrent episodes of blood oxygen desaturation and also disrupts normal sleep architecture. During episodes of total breathing cessation (apnea) or partial (hypopnea), blood oxygen saturation can fall to harmfully low levels, resulting in repeated hypoxic periods.
DEFINITION:
Partial pressure of oxygen (PaO2)
Partial pressure refers to the pressure exerted independently by a specific gas within a larger mix of gases. The partial pressure of arterial oxygen (PaO2) in healthy adults at sea level is typically 95-100 mm Hg. When this level rapidly drops, complex cognitive processes, memory, and judgment show impairment.
DEFINITION:
Watershed Region
In the brain, refers to overlapping border zones between the distal supplies of two arteries. For example, the region supplied by the distal branches of the middle and anterior cerebral arteries is a watershed region. Watershed regions are particularly vulnerable to the effects of hypoxia/ischemia.
Which of the following regions of the brain would likely be LEAST sensitive to the effects of anoxia/hypoxia?
A) Hippocampus
B) Globus Pallidus
C) Broca’s area
D) cerebellar Purkinje cells
C - Broca’s Area
Brain regions most sensitive to anoxia/hypoxia include those with the highest metabolic demand and those in watershed or distal regions of the cerebral vascular system. Although all brain regions are vulnerable if anoxia/hypoxia is severe, in general, regions with robust vascular supply (e.g., Broca’s area) are less vulnerable).
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Intelligence/Achievement
Not typically affected, but overall scores may be reduced due to impairments in processing speed and efficiency
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Attention/Concentration
Gross confusion is often present very early in recovery.
Impaired attention and concentration continue to be long-term issues.
Distractability often early and late in the process.
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Processing Speed
often impaired both cognitively and motorically
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Language
Formal language disorders are rarely seen.
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Visuospatial
if watershed zones are affected, deficits can be noticeable.
Lower performance might be related to slow information processing
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Memory
Impairments in storage, capacity, and retrieval are common.
Severe cases with bilateral hippocampal damage, a marked amnestic state may be evident.
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Executive Functions
Milder cases – minimally affected
Severe – some ppl sustain orbitofrontal damage b/c this is a watershed region.
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Sensorimotor Functions
Severe – can lead to spastic quadriparesis, ataxia, parkinsonism syndromes, and other motor impairments
Risk – basal ganglia and cerebellum are at high risk for injury
What are the expectations for Neuropsych after Hypoxia/Ischemia:
Emotion and Personality
1) Anosagnosia – impaired self awareness; 2)
Depression; 3) Changes in self-regulation
Which of the following would be expected to show the lowest vulnerability to the effects of anoxia/hypoxia?
a) areas supplied by the lenticulostriate arteries
b) watershed regions between the major arteries
c) regions with high metabolic demand
d) area of bifurcation of the major branches of the middle cerebral artery
D - area of bifurcation of the major branches of the middle cerebral artery
Ischemia is defined as ____.
a) a total lack of oxygen in the arterial blood
b) failure of perfusion of blood through the cerebral vessels to tissue
c) excessive carbon dioxide in the blood
d) insufficient expiration through the pulmonary system
B - failure of perfusion of blood through the cerebral vessels to tissue
Ischemia results from loss of perfusion of blood supply, in contrast to when there is adequate supply but low or lack of oxygen content (anoxia/hypoxia). In most severe cases, both ischemia and anoxia/hypoxia exist.
Under anoxic/hypoxic conditions, when neurons can no longer replenish ATP, the following response occurs:
a) neurons begin to self-hibernate so as to minimize metabolic processes
b) the brain diverts stored ATP from other brain regions to the hypoxic area
c) a series of neurotoxic processes are initiated that lead to neuronal death
d) axons rapidly rupture and disintigrate
C - A series of neurotoxic processes are initiated that lead to neuronal death
Neurons store virtually no energy and thus loss of O2 and glucose result in rapid ATP depletion. If not rapidly pursued, neuronal death occurs.
A complete loss of oxygen in the arterial blood or tissues is referred to as ___.
a) hyponatremia
b) anoxia
c) hypoxemia
d) apoptosis
B - Anoxia
The pattern of anoxic/hypoxic brain injury in neonates found to be most strongly associated with long-term outcome is injury to which areas?
a) basal ganglia and thalamus
b) deep brainstem nuclei
c) watershed regions
d) dorsolateral prefrontal cortex
A - basal ganglia and thalamus
The predominant pattern of brain injury in neonates found to be most strongly associated with long-term outcome, more so than the severity of injury in any given region, is injury to the basal ganglia and thalamus.
Which of the following cognitive disorders are least likely to be seen following hypoxic/ischemic damage?
a) amnestic syndrome
b) visuospatial deficits
c) impaired processing speed
d) impaired attention/working memory
B - visuospatial deficits
Impaired memory, processing speed, and attention are common cognitive problems following hypoxia/ischemia. Visuospatial deficits are much less commonly seen.
In severe cases of anoxic/hypoxic injury involving basal ganglia and cerebellar structures, you would be least likely to observe ____.
a) spastic quadriparesis
b) ataxia
c) homonymous hemianopsia
d) dystonia
C - homonymous hemianopsia
Severe hypoxic injury can cause spastic quadriparesis, ataxia, and other motor impairments/dysfunction. A homonymous hemianopsia (visual field defect) would be least likely in this case. Visual impairments may be observed when injury involves watershed zones.
of the following areas of functioning, which neuropsychological domain tends to be most resilient to anoxic/hypoxic injury?
a) contextual verbal memory
b) information processing speed
c) visuospatial memory
d) intellectual functioning
D - intellectual functioning
Hold tests are not typically affected, but overall scores may be reduced due to impairments in processing speed and efficiency.
Which of the following is a poor prognostic indicator for functional recovery from an anoxic/hypoxic incident?
a) amnesia for the first day of hospitalization
b) coma longer than 6 hours
c) Glasgow Coma Scale of >12
d) seizure on day of admission
B - coma longer than 6 hours
Coma is a poor prognostic indicator.
A syncopal episode would suggest a very brief loss of consciousness that would be unlikely, in and of itself, to cause any lasting injury.
