An arterial blood gas (ABG) is a test that measures the oxygen tension (PaO2), carbon dioxide tension (PaCO2), acidity (pH), oxyhemoglobin saturation (SaO2), and bicarbonate (HCO3) concentration in arterial blood. Some blood gas analyzers also measure the methemoglobin, carboxyhemoglobin, and hemoglobin levels. Such information is vital when caring for patients with critical illness or respiratory disease. As a result, the ABG is one of the most common tests performed on patients in intensive care units (ICUs).
The sites, techniques, and complications of arterial sampling are reviewed here, as well as the transport and analysis of the arterial blood. Normal ABG values are provided and a common clinical situation in which the ABG results may be misleading is also described. Interpretation of abnormal ABG values and venous blood gases are discussed separately. (See "Simple and mixed acid-base disorders" and "Venous blood gases and other alternatives to arterial blood gases".)
Arterial blood is required for an ABG. It can be obtained by percutaneous needle puncture or from an indwelling arterial catheter.
Needle puncture — Percutaneous needle puncture refers to the withdrawal of arterial blood via a needle stick. It needs to be repeated every time an ABG is performed, since an indwelling catheter is not inserted.
Site selection — The initial step in percutaneous needle puncture is locating a palpable artery. Common sites include the radial, femoral, brachial, dorsalis pedis, or axillary artery. There is no evidence that any site is superior to the others. However, the radial artery is used most often because it is accessible, easily positioned, and more comfortable for the patient than the alternative sites.