![]() Oxygen saturation as measured by pulse oximetry Oxygen saturation of the hemoglobin of arterial blood The term formerly used ( A-a D O 2) is discouraged.Īlveolar-arterial tension ratio P aO 2: P AO 2 The term oxygen exchange index describes this ratio. ▼ Blood gas, acid-base, and gas exchange terms P aO 2Īrterial oxygen tension, or partial pressureĪlveolar oxygen tension, or partial pressureĪrterial carbon dioxide tension, or partial pressureĪlveolar carbon dioxide tension, or partial pressureĪlveolar-arterial oxygen tension difference. These problems are discussed further in Chapter 40 in relation to pulmonary gaseous exchange and in Chapter 43 in relation to certain pulmonary diseases.Quick facts: PaO2, PAO2, PaCO2, PACO2, PvO2. In a normal person, the anatomical and physiological dead spaces are nearly equal because all alveoli are functional in the normal lung, but in a person with partially functional or nonfunctional alveoli in some parts of the lungs, the physiological dead space may be as much as 10 times the volume of the anatomical dead space, or 1 to 2 liters. When the alveolar dead space is included in the total measurement of dead space, this is called the physiological dead space, in contradistinction to the anatomical dead space. Therefore, from a functional point of view, these alveoli must also be considered dead space. On occasion, some of the alveoli are nonfunctional or only partially functional because of absent or poor blood flow through the adjacent pulmonary capillaries. The method just described for measuring the dead space (see slide 36) measures the volume of all the space of the respiratory system other than the alveoli and their other closely related gas exchange areas this space is called the anatomic dead space.
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