A practitioner will typically order an ABG analysis as one of the first tests to assess respiratory status because it helps evaluate gas exchange in the lungs. ABG analysis includes several measures:
- An indication of hydrogen ion concentration in the blood, pH shows the blood’s acidity or alkalinity.
- Known as the respiratory parameter, partial pressure of arterial carbon dioxide (PaCO2), reflects the adequacy of the lungs’ ventilation and carbon dioxide elimination.
- Partial pressure of arterial oxygen (PaO2) reflects the body’s ability to pick up oxygen from the lungs.
- Known as the metabolic parameter, the bicarbonate (HCO3 –) level reflects the kidneys’ ability to retain and excrete bicarbonate.
ABG analysis is one of the first tests used to assess respiratory status because it evaluates gas exchange in the lungs.
- Blood for an ABG analysis should be drawn from an arterial line if the patient has one. If a percutaneous puncture is necessary, the site must be chosen carefully. The brachial, radial, or femoral arteries can be used.
- After the sample is obtained, apply pressure to the puncture site for 5 minutes and tape a gauze pad firmly in place. (Don’t apply tape around the arm; it could restrict circulation.) Regularly monitor the site for bleeding, and check the arm for signs of complications, such as swelling, discoloration, pain, numbness, and tingling.
- Make sure you note on the slip whether the patient is breathing room air or oxygen. If oxygen, document the number of liters. If the patient is receiving mechanical ventilation, document the fraction of inspired oxygen. Also include the patient’s temperature on the slip; results may be corrected if the patient has a fever or hypothermia.
- Keep in mind that certain conditions may interfere with test results — for example, failing to properly heparinize the syringe before drawing a blood sample or exposing the sample to air. Venous blood in the sample may lower PaO2 levels and elevate PaCO2 levels.