AP: Cerebral Hypoxia, Stroke and Cerebral Haemorrhage Flashcards
What is the difference between hypoxia and ischaemia?
- Hypoxia is reduced oxygen supply.
- Doesn’t necessarily cause damage to nerve tissue.
- Ischaemia is reduction in blood supply.
- A reduction in oxygen itself will not affect the brain unless it goes long enough for the heartbeat to be affected.
What is the mechanism in hypoxemia? (6 points)
- Mechanisms to maintain oxygenation and cerebral metabolic rate
- Hyperventilation increases tidal volume
- Brain takes more oxygen out of blood
- Cerebral blood flow increases
- Erythropoietin production
- Neovascularisation of the brain
What is anaemic hypoxia?
Low blood haemoglobin (because of anaemia) causes decreased oxygen carrying capacity.
- What is histotoxic hypoxia?
- What two toxins does it involve?
- Inability of the tissue to utilise oxygen - exogenous or endogenous.
- Involves environmental toxins such as cyanide and sulfide.
What is the affinity of CO for Hb compared to Oxygen?
200x
Explain the process of carbon monoxide poisoning
- Effect is similar to anaemic hypoxia
- Permanent until new red blood cells are produced
- CO binds to receptors in the brain rich in haem iron (directly, causing necrosis)
- globus pallidus
- pars reticulata of the substantia nigra
- CO is cardiotoxic and hypotension results
What are the 2 different types of pathology in hypoxia?
- Selective neuronal necrosis - only the neurones are affected as they are the most vulnerable cells
- Pan-necrosis - all the tissue elements undergo death: neurones, glia and vessels
What are the 5 kinds of asphyxia?
- Environmental - insufficienct oxygen in air e.g. child in refrigerator
- Toxic - competiting for oxygen e.g. CO
- Mechanical - airways are blocked in an unnatural fashion - e.g. postural asphyxia
- Pathological - respiratory diseases
- Iatrogenic - divers, anaesthesia
- The hippocampus and the cerebellum are two regions of the brain most affected in asphyxia. What region/area/cells are first affected in these areas?
- What are the other three areas most affected in asphyxia?
- Hippocampus - CA1 region first affected.
- Cerebellum - Purkinje cells first affected (need 4-6 hour survival time post injury for changes to be seen).
- Thalamus.
- Basal ganglia.
- Brainstem.
Why distinguish clinically between hypoxia and ischaemia?
- To predict the clinical outcome of a global insult and coma.
- Hypoxic coma can be followed by a complete recovery; non-perfused brain results in brain death.
What is a subarachnoid haemorrhage?
Bleeding occuring in the sub-arachnoid space.
What are 3 causes of non-traumatic subarachnoid haemorrhage?
- Rupture of a saccular (berry) aneurysm:
- small thin walled protrusion from arteries of Circle of Willis and major branches
- Arteriovenous malformations:
- Abnormal development of vessels - 5% have saccular aneurysm on feeding vessels
- Other aneurysms:
- Fusiform: atherosclerotic
- Mycotic: infectious - septic embolus weakens vessel wall there it lodges
- Traumatic - old traumatic injury that ruptures later
What are the presentations of a subarachnoid haemorrhage?
- Is it accepted as a sudden cause of death?
- What symptoms?
- Not accepted as sudden cause of death.
- May present with warning symptoms.
- Severe headache few days to weeks before rupture.
- Ruptures when physically active/stressed/hypertension.
- Severe generalised headache.
- Vomiting.
- Rapid LOC or similar but lucid interval.
Astrocytes, oligodendrocytes, vascular cells, and neurons are all affected in ischaemic stroke. What is the order that these cells are affected?
- Neurons.
- Oligodendrocytes.
- Astrocytes.
- Vascular cells.
What are the 2 kinds of ischaemic strokes?
- Focal cerebral ischaemia.
- Global cerebral ischaemia.