Arterial Blood Gas Analysis (ABG)
Arterial blood gas (ABG) analysis is used to measure the partial pressures of oxygen (PaO2) and carbon dioxide (pacO2)' and the pH of an arterial sample. Oxygen content (O2CT), oxygen saturation (SaO2) and bicarbonate (RCO3 -) values are also measured. A blood sample for ABG analysis may be drawn by percutaneous arterial puncture or from an arterial line.
Procedure and posttest care
Normal ABG values fall within the following ranges:
Low PaO2, O2CT, and SaO2 levels and a high PacO2 may result from conditions that impair respiratory function, such as respiratory muscle weakness or paralysis, respiratory center inhibition (from head injury, brain tumor, or drug abuse, for example), and airway obstruction (possibly from mucus plugs or a tumor). Similarly, low readings may result from bronchiole obstruction caused by asthma or emphysema, from an abnormal ventilation-perfusion ratio due to partially blocked alveoli or pulmonary capillaries, or from alveoli that are damaged or filled with fluid because of disease, hemorrhage, or near-drowning.
When inspired air contains insufficient oxygen, PaO2, O2CT, and SaO2 decrease, but PacO2 may be normal. Such findings are common in pneumothorax, impaired diffusion between alveoli and blood (due to interstitial fibrosis, for example), or an arteriovenous shunt that permits blood to bypass the lungs.
Low O2CT - with normal PaO2, Sa02 and, possibly, PacO2 values may result from severe anemia, decreased blood volume, and reduced hemoglobin oxygen-carrying capacity.
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