Résumé
Hypoxemia is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body. Hypoxemia refers to the low level of oxygen in blood, and the more general term hypoxia is an abnormally low oxygen content in any tissue or organ, or the body as a whole. Hypoxemia can cause hypoxia (hypoxemic hypoxia), but hypoxia can also occur via other mechanisms, such as anemia. Hypoxemia is usually defined in terms of reduced partial pressure of oxygen (mm Hg) in arterial blood, but also in terms of reduced content of oxygen (ml oxygen per dl blood) or percentage saturation of hemoglobin (the oxygen-binding protein within red blood cells) with oxygen, which is either found singly or in combination. While there is general agreement that an arterial blood gas measurement which shows that the partial pressure of oxygen is lower than normal constitutes hypoxemia, there is less agreement concerning whether the oxygen content of blood is relevant in determining hypoxemia. This definition would include oxygen carried by hemoglobin. The oxygen content of blood is thus sometimes viewed as a measure of tissue delivery rather than hypoxemia. Just as extreme hypoxia can be called anoxia, extreme hypoxemia can be called anoxemia. Hypoxia (medical)#Signs and symptoms In an acute context, hypoxemia can cause symptoms such as those in respiratory distress. These include breathlessness, an increased rate of breathing, use of the chest and abdominal muscles to breathe, and lip pursing. Chronic hypoxemia may be compensated or uncompensated. The compensation may cause symptoms to be overlooked initially, however, further disease or a stress such as any increase in oxygen demand may finally unmask the existing hypoxemia. In a compensated state, blood vessels supplying less-ventilated areas of the lung may selectively contract, to redirect the blood to areas of the lungs which are better ventilated.
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