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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.
Hypoxia can be due to external causes, when the breathing gas is hypoxic, or internal causes, such as reduced effectiveness of gas transfer in the lungs, reduced capacity of the blood to carry oxygen, compromised general or local perfusion, or inability of the affected tissues to extract oxygen from, or metabolically process, an adequate supply ...
A drop in the oxygen carried in the blood is known as hypoxemia; a rise in arterial carbon dioxide levels is called hypercapnia. Respiratory failure is classified as either Type 1 or Type 2, based on whether there is a high carbon dioxide level, and can be acute or chronic.
An SaO 2 (arterial oxygen saturation) value below 90% causes hypoxia (which can also be caused by anemia). Hypoxia due to low SaO 2 is indicated by cyanosis, but oxygen saturation does not directly reflect tissue oxygenation. The affinity of hemoglobin to oxygen may impair or enhance oxygen release at the tissue level.
A pulmonary shunt is the passage of deoxygenated blood from the right side of the heart to the left without participation in gas exchange in the pulmonary capillaries. It is a pathological condition that results when the alveoli of parts of the lungs are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region.
While the maintenance of ventilation/perfusion ratio during regional obstruction of airflow is beneficial, HPV can be detrimental during global alveolar hypoxia which occurs with exposure to high altitude, where HPV causes a significant increase in total pulmonary vascular resistance, and pulmonary arterial pressure, potentially leading to ...
[5] The A-a gradient has clinical utility in patients with hypoxemia of undetermined etiology. The A-a gradient can be broken down categorically as either elevated or normal. Causes of hypoxemia will fall into either category. To better understand which etiologies of hypoxemia falls in either category, we can use a simple analogy.
Generalized hypoxia is a medical condition in which the tissues of the body are deprived of the necessary levels of oxygen due to an insufficient supply of oxygen, which may be due to the composition or pressure of the breathing gas, decreased lung ventilation, or respiratory disease, any of which may cause a lower than normal oxygen content in the arterial blood, and consequently a reduced ...