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Arterial blood oxygen tension (normal) P a O 2 – Partial pressure of oxygen at sea level (160 mmHg (21.3 kPa ) in the atmosphere, 21% of the standard atmospheric pressure of 760 mmHg (101 kPa)) in arterial blood is between 75 and 100 mmHg (10.0 and 13.3 kPa).
Normal arterial blood oxygen saturation levels in humans are 96–100 percent. [1] If the level is below 90 percent, it is considered low and called hypoxemia . [ 2 ] Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed.
Applying this analogy to different causes of hypoxemia should help reason out whether to expect an elevated or normal A-a gradient. As a general rule of thumb, any pathology of the alveolar-capillary unit will result in a high A-a gradient. The table below has the different disease states that cause hypoxemia. [2]
This is an important mechanism for maintaining arterial blood pO2, pCO2, and pH within appropriate physiological ranges. For example, a fall in arterial pO2 ( hypoxemia ) or an increase in arterial pCO2 (hypercapnia) leads to an increase in the rate and depth of respiration through activation of the chemoreceptor reflex.
Hypoxemia refers to insufficient oxygen in the blood. Thus any cause that influences the rate or volume of air entering the lungs (ventilation) or any cause that influences the transfer of air from the lungs to the blood may cause hypoxemia. As well as these respiratory causes, cardiovascular causes such as shunts may also result in hypoxemia.
The normal range for pH is 7.35–7.45. As the pH decreases (< 7.35), it implies acidosis, while if the pH increases (> 7.45) it implies alkalosis. In the context of arterial blood gases, the most common occurrence will be that of respiratory acidosis. Carbon dioxide is dissolved in the blood as carbonic acid, a weak acid; however, in large ...
Because of the increased dead space ventilation, the arterial pO 2 is reduced and thus also the peripheral oxygen saturation is lower than normal, leading to tachypnea and dyspnea. This finding is typically associated with pulmonary embolism (where blood circulation is impaired by an embolus). Ventilation is wasted, as it fails to oxygenate any ...
Hypoxemic hypoxia is a lack of oxygen caused by low oxygen tension in the arterial blood, due to the inability of the lungs to sufficiently oxygenate the blood. Causes include hypoventilation, impaired alveolar diffusion, and pulmonary shunting. [8] This definition overlaps considerably with that of hypoxic hypoxia.