Blood oxygen content, or oxygen saturation, is the sum of dissolved and bound oxygen as present in arterial and venous blood. Oxygen is supplied to all cells and tissues of the body via the blood. In phenomena such as carbon monoxide poisoning, this supply is no longer guaranteed.
What is oxygen saturation?
Blood oxygen content, or oxygen saturation, is the sum of dissolved and bound oxygen as it exists in arterial and venous blood. In pulmonary respiration, blood performs the role of a transport medium. Erythrocytes are the most abundant blood cells in human blood and are also called red blood cells. They can take up oxygen and, due to their biconcave shape, fit through the thinnest capillaries. From the pulmonary capillaries, they transport oxygen through the blood system to organs throughout the body. There are 24 to 30 trillion erythrocytes in the blood. They determined the oxygen content that is present in the blood. This oxygen content has medical relevance mainly as oxygen saturation. Oxygen saturation is the quotient of the actual blood oxygen and the maximum blood oxygen capacity. Normally, the oxygen content in the blood is expressed in the unit ml/dl. The gas volume of oxygen is calculated in milliliters per 100 milliliters of blood. The oxygen content can refer to either the arterial or venous oxygen content in the blood. For arteries, the value is called CaO2. For veins, on the other hand, it is called CvO2. Arterial oxygen, in particular, is highly significant medically.
Function and task
Oxygen is transported in the blood in two different ways. First, it is in a physically dissolved form, and second, it is bound to the hemoglobin of red blood cells. The dissolved form of oxygen in the blood is used for oxygen exchange between the blood plasma and the alveoli of the lungs. In addition, the dissolved form plays a role in diffusion-based exchange between the blood plasma and organs, tissues, and cells. The dissolved oxygen concentration at a conventional partial pressure of oxygen in the alveoli is about three milliliters in the plasma of one liter of blood. However, oxygen has a limited solubility. For this reason, it is bound to the divalent iron of hemoglobin. This process is also known as oxygenation and ensures the supply of oxygen to all cells in the body. During oxygenation, the molecules of hemoglobin rearrange themselves. The central iron atom of the compound changes its position. With the bond, the hemoglobin is in a relaxed R-form, also known as oxyhemoglobin. How affine the hemoglobin is to oxygen depends on several factors. The ph value and the temperature play a central role. When the carbon dioxide content in the blood is low and the pH is relatively high, hemoglobin has an affinity for oxygen. In the alveolar capillaries of the lungs, a high pH is present, while the carbon dioxide content is comparatively low. Therefore, hemoglobin binds to oxygen in the capillaries of the lungs. In the rest of the body, relatively high CO2 concentrations are present at a relatively low pH. For this reason, deoxygenation occurs. Hemoglobin thus slowly releases the oxygen because its binding affinity is reduced. In this way, the entire body can be supplied with oxygen. Oxygen is needed for the metabolic processes of all cells. These metabolic processes are therefore also called internal respiration and provide the organism with energy. Without blood oxygen in its dissolved and bound form, the metabolic processes of the cells would be threatened and, as a result, the body’s energy supply would no longer be guaranteed.
Diseases and ailments
When arterial oxygen levels fall below the standard values of 20.4 ml/dl in men and 18.6 ml/dl in women, hypoxemia is present. Such a phenomenon may occur, for example, in the context of carbon monoxide poisoning. It is the main cause of fatal poisoning. The supply of oxygen to the tissues is no longer assured in carbon monoxide poisoning. CO2 displaces oxygen in the blood from the hemoglobin and oxygen can thus no longer be transported through the body. The consequences can be fatal under certain circumstances.Hypoxemia may also develop in respiratory insufficiency. The alveoli are under-ventilated in the context of this phenomenon. Feelings of suffocation occur. Acute pneumonia is often the cause of respiratory insufficiency. A third cause of hypoxemia may be anemia (anemia). As part of this phenomenon, the hemoglobin concentration in the blood drops. The ability to bind oxygen decreases. As a rule, the body tries to compensate for the lack of erythrocytes, and thus hemoglobin, by increasing the heart rate. In this way, the organism wants to ensure oxygen supply to the internal organs despite the anemia. Anemias usually present themselves as a result of a major blood loss. Blood formation disorders, kidney diseases or tumor diseases and chronic inflammatory diseases are also conceivable causes. Faster fatigability and shortage of air are the most common accompanying symptoms of anemia. Hypoxemia must be distinguished from hypoxemia. In this case, parts of the body are no longer supplied with sufficient oxygen. Fainting and a blue-grayish skin color set in. Hypoxia can have ischemic, anemic, or histotoxic causes, for example.
