What happens when blood-oxygen levels are too low?

Written by jennifer lanier
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The cells of the body need a constant supply of oxygen. When oxygen supply is reduced or interrupted, a person may develop hypoxaemia, a low level of oxygen in the blood.

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Hypoxaemia can disrupt body function and damage vital tissues. In extreme cases, hypoxaemia can be life-threatening.


The first and most common symptom of hypoxaemia is shortness of breath. In some cases, symptoms of weakness, fatigue and confusion are also present.


Low blood-oxygen levels eventually affect every system of the body as organ function deteriorates.


Common causes of low blood oxygen levels are heart or lung disease, anaemia, strenuous exercise, carbon monoxide poisoning, emphysema, pneumonia, shock, shallow breathing, stress and sleep apnoea.

Measuring Blood Oxygen

Blood oxygen can be measured by an arterial blood test or by an oximeter, a device that clips onto the finger. At sea level, normal blood oxygen readings are between 95 and 100 per cent. Readings under 90 are considered low. At levels below 80 per cent, the condition is considered severe.


Medical treatment for hypoxaemia involves administering oxygen by face mask or mechanical ventilation. Doctors may also recommend regular exercise to strengthen the respiratory muscles and avoiding cigarette smoke.

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