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An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide.An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe and a thin needle, [1] but sometimes the femoral artery in the groin or another site is used.
Recall that the relationship represented in a Davenport diagram is a relationship between three variables: P CO 2, bicarbonate concentration and pH.Thus, Fig. 7 can be thought of as a topographical map—that is, a two-dimensional representation of a three-dimensional surface—where each isopleth indicates a different partial pressure or “altitude.”
Example: patient who is receiving an FiO2 of .5 (i.e., 50%) with a measured PaO2 of 60 mmHg has a PaO 2 /FiO 2 ratio of 120. In healthy lungs, the Horowitz index depends on age and usually falls between 350 and 450. A value below 300 is the threshold for mild lung injury, and 200 is indicative of a moderately severe lung injury.
A blood gas test or blood gas analysis tests blood to measure blood gas tension values, it also measures blood pH, and the level and base excess of bicarbonate.The source of the blood is reflected in the name of each test; arterial blood gases come from arteries, venous blood gases come from veins and capillary blood gases come from capillaries. [1]
Because A–a gradient is approximated as: (150 − 5/4(PCO 2)) – PaO 2 at sea level and on room air (0.21x(760-47) = 149.7 mmHg for the alveolar oxygen partial pressure, after accounting for the water vapor), the direct mathematical cause of a large value is that the blood has a low PaO 2, a low PaCO 2, or both.
The formation of a bicarbonate ion will release a proton into the plasma, decreasing pH (increased acidity), which also shifts the curve to the right as discussed above; low CO 2 levels in the blood stream results in a high pH, and thus provides more optimal binding conditions for hemoglobin and O 2. This is a physiologically favored mechanism ...
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The most common gas tensions measured are oxygen tension (P x O 2), carbon dioxide tension (P x CO 2) and carbon monoxide tension (P x CO). [3] The subscript x in each symbol represents the source of the gas being measured: "a" meaning arterial, "A" being alveolar, "v" being venous, and "c" being capillary. [3] Blood gas tests (such as arterial ...