Friday, December 24, 2010

Arterial Blood Gases ABG

Arterial Blood Gases ABG. Blood Gases Also known as: Arterial blood gases; ABGs; pH; PO2; PCO2; Bicarbonate; HCO3-; Oxygen saturation Formal name: Blood Gases
Blood gases are a group of tests that are performed together to measure the pH and the amount of oxygen (O2) and carbon dioxide (CO2) present in a sample of blood (usually from the arteries). The body carefully regulates blood pH, maintaining it within a narrow range of 7.35-7.45, not too acidic (acidosis) or too alkaline/basic (alkalosis).
There are a wide range of acute and chronic conditions that can affect kidney function, acid production, or lung function, and that have the potential to cause a pH, carbon dioxide/oxygen, or electrolyte imbalance. Examples include uncontrolled diabetes, which can lead to ketoacidosis and metabolic acidosis, and severe lung diseases that can affect carbon dioxide/oxygen gas exchanges. Even temporary conditions such as shock, anxiety, pain, prolonged vomiting, and severe diarrhea can sometimes lead to acidosis or alkalosis.
Blood gas tests give a snapshot of the blood's pH and oxygen and carbon dioxide content. They directly measure:
  • pH - a measure of the balance of acid and bases in the blood. Blood pH decreases, becoming more acidic, with increased amounts of carbon dioxide (PCO2) and other acids. Blood pH increases, becoming more alkaline, with decreased carbon dioxide or increased amounts of bases like bicarbonate (HCO3-).
  • Partial pressure of O2 (PO2) - the amount of oxygen gas in blood.
  • Partial pressure of CO2 (PCO2) - the amount of carbon dioxide gas in the blood. As PCO2 levels rise, blood pH levels decrease, becoming more acidic; as PCO2 decreases, pH levels rise, making the blood more basic (alkaline).

Arterial blood is almost always used for blood gas analysis, but in some cases, such as for babies, whole blood from heelsticks is used. Blood may also be taken from the umbilical cord of a newborn. Since arterial blood carries oxygen to the body and venous blood carries waste products to the lungs and kidneys, the gas and pH levels will not be the same in both.
An arterial blood sample is usually collected from the radial artery in the wrist, located on the inside of the wrist, below the thumb, where the pulse can be felt. A circulation test called an Allen test will be done before the collection to make sure that there is adequate circulation in your wrist. The test involves compressing both the radial and the ulnar wrist arteries, then releasing each in turn to watch for "flushing," the pinking of the skin as blood returns to your hand. If one hand does not flush, then the other wrist will be tested. Blood can also be collected from the brachial artery in the elbow or the femoral artery in the groin. These sample locations require special training to properly access, so the collection is often performed by a doctor. In newborns that experience difficulty in breathing right after birth, blood may be collected from both the umbilical artery and vein and tested separately.
After an arterial blood draw, pressure must be firmly applied to the site for at least 5 minutes. Since blood pumps through the artery, the puncture will take awhile to stop bleeding. If you are taking blood thinners or aspirin, it may take as long as ten to fifteen minutes to stop bleeding. The person collecting the sample will verify that the bleeding has stopped and will put a wrap around your wrist, which should be left in place for an hour or so.


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