ABG interpretation: metabolic acidosis; which accompanying ABG finding is expected?

ABG interpretation: metabolic acidosis; which accompanying ABG finding is expected?

• A. Decreased bicarbonate (HCO3-)
• B. Normal PaO2
• C. Elevated PaCO2
• D. Increased bicarbonate

Answer: (A)

Metabolic acidosis lowers the blood’s buffering capacity, so bicarbonate (HCO3-) falls as it neutralizes excess acids or as base is lost. On ABG, this shows up as a decreased HCO3-, with the pH decreased as well. The body compensates by breathing more rapidly to blow off CO2, so PaCO2 tends to be lower rather than higher. Therefore, the accompanying ABG finding you’d expect is a decreased bicarbonate level. Normal PaO2 can occur, but it doesn’t define the problem, and an elevated PaCO2 or increased bicarbonate would point to different conditions (respiratory acidosis or metabolic alkalosis, respectively).

Metabolic acidosis lowers the blood’s buffering capacity, so bicarbonate (HCO3-) falls as it neutralizes excess acids or as base is lost. On ABG, this shows up as a decreased HCO3-, with the pH decreased as well. The body compensates by breathing more rapidly to blow off CO2, so PaCO2 tends to be lower rather than higher. Therefore, the accompanying ABG finding you’d expect is a decreased bicarbonate level. Normal PaO2 can occur, but it doesn’t define the problem, and an elevated PaCO2 or increased bicarbonate would point to different conditions (respiratory acidosis or metabolic alkalosis, respectively).