EFFECTS OF HYPOXIA
Acute and severe hypoxia leads to
unconsciousness. If not treated immediately, brain death occurs. Chronic hypoxia
produces various symptoms in the body.
Effects of hypoxia are of two types:
1. Immediate effects
2. Delayed effects.
Immediate Effects
i. Effects on blood
Hypoxia induces secretion of erythropoietin from kidney. Erythropoietin
increases production of RBC. This in turn, increases the oxygen carrying
capacity of blood.
ii. Effects on cardiovascular
system
Initially, due to the
reflex stimulation of cardiac and vasomotor centers, there is an increase in
rate and
force of contraction of heart, cardiac
output and blood pressure. Later, there is reduction in the rate and force of contraction
of heart. Cardiac output and blood pressure
are also decreased.
iii. Effects on respiration
Initially, respiratory rate increases
due to chemoreceptor reflex. Because of this, large amount of carbon
dioxide is
washed out leading to alkalemia.
Later,
the respiration tends to be shallow and periodic. Finally, the rate and force
of breathing are reduced to a great extent due to the failure of respiratory centers.
iv. Effects on digestive system
Hypoxia is associated with loss of
appetite, nausea and vomiting. Mouth becomes dry and there is a
feeling of
thirst.
v. Effects on kidneys
Hypoxia causes increased secretion of
erythropoietin from the juxtaglomerular apparatus. And alkaline urine is excreted.
vi. Effects on central nervous
system
In mild hypoxia, the symptoms are
similar to those of alcoholic
intoxication.
Individual is depressed,
apathetic with general loss
of self control. The person becomes talkative,
quarrelsome, ill-tempered and rude.
The person starts shouting, singing or crying. There is disorientation
and loss of discriminative ability and loss of power of judgment.
Memory is
impaired. Weakness, lack of coordination and fatigue of muscles are
common in hypoxia. If hypoxia is acute and severe, there is a sudden loss of
consciousness. If not treated immediately, coma occurs, which leads to death.
Delayed Effects of
Hypoxia
Delayed effects appear
depending upon the length and severity of the exposure to hypoxia. The
person becomes highly irritable and develops the symptoms of mountain sickness,
such as nausea, vomiting, depression, weakness and fatigue.
TREATMENT FOR HYPOXIA
– OXYGEN THERAPY
Best treatment for
hypoxia is oxygen therapy, i.e. treating the affected person with oxygen. Pure
oxygen or oxygen combined with another gas is administered.
Oxygen therapy is
carried out by two methods:
1. By placing the
patient’s head in a ‘tent’ containing oxygen
2. By allowing the patient
to breathe oxygen either from
a mask or an intranasal tube.
Depending upon the
situation, oxygen therapy can be given either under normal atmospheric pressure
or
under high pressure
(hyperbaric oxygen).
In Normal Atmospheric
Pressure
With normal atmospheric pressure, i.e.
at one atmosphere (760 mm Hg), administration of pure oxygen is
well tolerated by the
patient for long hours. However, after 8 hours or more, lung tissues show fluid
effusion and
edema. Other tissues are not affected very much because of hemoglobin-oxygen
buffer system.
In High Atmospheric
Pressure – Hyperbaric Oxygen
Hyperbaric oxygen is
the pure oxygen with high atmospheric pressure of 2 or more than 2 atmosphere.
Hyperbaric oxygen
therapy with 2 to 3
atmosphere is tolerated by the patient for about 5 hours. During
this period, the
dissolved form of oxygen increases in arterial blood because the oxygen
carrying capacity
of hemoglobin is
limited. At this level, tissue oxygen tension also increases to about 200 mm
Hg. However, tissues tolerate the high partial pressure of oxygen, without much
adverse effects. But, oxygen toxicity develops when pure oxygen is administered
for long periods. Refer oxygen toxicity below.
Efficacy of Oxygen Therapy in Different Types of Hypoxia
Oxygen therapy is the
best treatment for hypoxia. But it is not effective equally in all types of
hypoxia. Value of oxygen therapy depends upon the type of hypoxia.
So, before deciding the oxygen therapy, one should recall the physiological
basis of different types of hypoxia. In hypoxic hypoxia, the oxygen therapy is
100% useful. In anemic hypoxia, oxygen therapy is moderately effective to about
70%. In stagnant hypoxia, the effectiveness of oxygen therapy is less than 50%.
In histotoxic hypoxia, the oxygen therapy is not useful at all. It is because,
even if oxygen is delivered, the cells cannot utilize oxygen.
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