Hypoxia
Definition
A condition in which the body or a region of the body is deprived of adeuate oxygen at the tissue level.
Total deprivation : Anoxia
Hypoxia can be generalized or local
Causes of Hypoxia
High altitude - will lead to altitude sickness : high altitude pulmonary edema, high altitude cerebral edema
Diving underwater with closed circuit rebreather systems
Preterm birth
Types of Hypoxia
4 types
Hypoxemic type : spO2 in blood low - O2 going to tissues is low because the O2 in Hb is low
Anemic type : amount of functional Hb is too low
Stagnant type : flow of blood is low
Histotoxic type : tissue cell are poisoned and unable to make use of the O2 in circulation
Mechanisms
Hypoxemic type :
A decrease in the amount of breathable oxygen (pilots, mountain climbers, people living at high altitudes due to decreased barometric pressure
Cardiopulmonary failure in which the lungs are unable to efficiently transfer O2 from alveoli to blood
Anemic type : The total amount of Hb is too small to supply the needs, as in anemia, severe bleeding or is non functional as in CO poisoing, acquired methemoglobinemia
Stagnant type: blood flow through capillaries is insufficient : e.g. heart disease that impairs the circulation , impairment of venous return of blood or trauma that induces shock, Raynaud syndrome, Buerger disease, exposure to severe cold, tourniquets, overhelming systemic infection with shock
Histotoxic Type : the cells of the body are unable to use O2 - cyanide poisoning, narcotics, alcohol, formaldehyde, acetone - that it the cellular respiration is impaired
Symptoms and Signs
Generalized hypoxia
Fatigue
Numbness, tingling of extremities
Nausea
Ataxia
Confusion/disorientation/Hallucination/Behavioural changes
Severe headaches
Reduced level of consciousness
Papilloedema
Breathlessness
Pallor
Tachycardia
Pulmonary hypertension
Cyanosis
Slow heart rate
Cor pulmonale
Low blood pressure
Followed by death
Local Hypoxia
If local tissue is not perfused well it becomes cold and pale - may become cyanotic - gangrene
Ischaemia - decreased blood supply to an area causing local hypoxia - in the brain may lead to stroke and in the heart lead to angina pectoris and later on myocardial infarction
Cause of local hypoxia may be due to atheromatous plaques in the arteries, arteriospasm, thrombi, emboli
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